TTEK Tetra Tech Inc

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The accompanying unaudited consolidated financial statements and related notes of Tetra Tech, Inc. (“we,” “us,” “our” or "Tetra Tech") have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. They do not include all of the information and footnotes required by U.S. GAAP for complete financial statements and, therefore, should be read in conjunction with the audited consolidated financial statements and the notes contained in our Annual Report on Form 10-K for the fiscal year ended October 1, 2023.

These financial statements reflect all normal recurring adjustments that are considered necessary for a fair statement of our financial position, results of operations and cash flows for the interim periods presented. The results of operations and cash flows for any interim period are not necessarily indicative of results for the full fiscal year or for future fiscal years. Certain prior year amounts have been reclassified to conform to the current year presentation in the accompanying notes.

In November 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update (“ASU”) No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which requires that an entity report segment information in accordance with Topic 280, Segment Reporting. The amendments in the ASU are intended to improve reportable segment disclosure requirements primarily through enhanced disclosures about significant segment expenses. The amendments in this ASU are effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024 (fiscal 2025 for us). Early adoption is permitted. We are currently evaluating the impact of this guidance on our consolidated financial statements; however, we do not plan to adopt Topic 280 before fiscal 2025.

In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which requires that an entity, on an annual basis, disclose additional income tax information, primarily related to the rate reconciliation and income taxes paid. The amendments in the ASU are intended to enhance the transparency and decision usefulness of income tax disclosures. The amendments in this ASU are effective for annual periods beginning after December 15, 2024 (fiscal 2026 for us). Early adoption is permitted. We are currently evaluating the impact of this guidance on our consolidated financial statements; however, we do not plan to adopt Topic 740 before fiscal 2026.

We disaggregate revenue by client sector and contract type, as we believe it best depicts how the nature, timing and uncertainty of our revenue and cash flows are affected by economic factors. The following tables present our revenue disaggregated by client sector and contract type (in thousands):

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			Three Months Ended												Nine Months Ended
			June 30, 2024						July 2, 2023						June 30, 2024						July 2, 2023
Client Sector:
U.S. federal government (1)			$	432,242					$	338,022					$	1,221,320					$	996,471
U.S. state and local government			146,401						151,462						444,877						452,447
U.S. commercial			241,838						225,907						665,675						633,401
International (2)			523,842						493,556						1,492,333						1,179,619
Total			$	1,344,323					$	1,208,947					$	3,824,205					$	3,261,938
Contract Type:
Fixed-price			$	548,452					$	452,605					$	1,478,915					$	1,194,266
Time-and-materials			589,301						596,904						1,730,796						1,550,970
Cost-plus			206,570						159,438						614,494						516,702
Total			$	1,344,323					$	1,208,947					$	3,824,205					$	3,261,938

(1)    Includes revenue generated under U.S. federal government contracts performed outside the United States.

(2)    Includes revenue generated from non-U.S. clients, primarily in Canada, Australia, Europe and the United Kingdom.

Other than the U.S. federal government, no single client accounted for more than 10% of our revenue for the three and nine months ended June 30, 2024 and July 2, 2023.

Contract Assets and Contract Liabilities

We invoice customers based on the contractual terms of each contract. However, the timing of revenue recognition may differ from the timing of invoice issuance. Contract assets represent revenue recognized in excess of the amounts for which we have the contractual right to bill our customers. Such amounts are recoverable from customers based upon various measures of performance, including achievement of certain milestones or completion of a contract. In addition, many of our time-and-materials arrangements are billed in arrears pursuant to contract terms that are standard within the industry, resulting in contract assets and/or unbilled receivables being recorded, as revenue is recognized in advance of billings. Contract retentions, included in contract assets, represent amounts withheld by clients until certain conditions are met or the project is completed, which may extend beyond one year.

Contract liabilities consist of billings in excess of revenue recognized. Contract liabilities decrease as we recognize revenue from the satisfaction of the related performance obligation and increase as billings in advance of revenue recognition occur. Contract assets and liabilities are reported in a net position on a contract-by-contract basis at the end of each reporting period. There were no substantial non-current contract assets or liabilities for the periods presented. Net contract assets/liabilities consisted of the following (in thousands):

			Balance at
			June 30, 2024						October 1, 2023
Contract assets (1)			$	118,556					$	113,939
Contract liabilities			(372,283)						(335,044)
Net contract liabilities			$	(253,727)					$	(221,105)

(1)    Includes $6.2 million and $6.8 million of contract retentions at June 30, 2024 and October 1, 2023, respectively.

Both our contract assets and contract liabilities increased in the third quarter of fiscal 2024 compared to fiscal 2023 year-end, due to the timing of our milestone billing on fixed-price contracts which were different from the timing of revenue recognition on those contracts. For the first nine months of fiscal 2024 and 2023, we recognized revenue of approximately $214 million and $143 million, respectively, from the amounts included in the contract liability balances at the end of fiscal 2023 and 2022, respectively.

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Revenue is recognized by measuring progress over time under Accounting Standards Codification Topic 606, "Revenue from Contracts with Customers". We estimate and measure progress on our contracts over time whereby we compare our total costs incurred on each contract as a percentage of the total expected contract costs. Changes in those estimates could result in the recognition of cumulative catch-up adjustments to the contract’s inception-to-date revenue, costs and profit in the period in which such changes are made. As a result, for the third quarter and first nine months of fiscal 2024, we recognized net favorable revenue and operating income adjustments of $6.5 million and $16.4 million, respectively. For the first nine months of fiscal 2023, we recognized net favorable revenue and operating income adjustments of $4.0 million (substantially all in the first quarter).

Changes in revenue and cost estimates could also result in a projected loss, determined at the contract level, which would be recorded immediately in earnings. At June 30, 2024 and October 1, 2023, our consolidated balance sheets included liabilities for anticipated losses of $15.0 million and $8.5 million, respectively. The estimated cost to complete these related contracts was approximately $95 million and $68 million at June 30, 2024 and October 1, 2023, respectively.

Accounts Receivable, Net

Net accounts receivable consisted of the following (in thousands):

			Balance at
			June 30, 2024						October 1, 2023
Billed			$	685,184					$	672,712
Unbilled			372,913						306,788
Total accounts receivable			1,058,097						979,500
Allowance for doubtful accounts			(4,339)						(4,965)
Total accounts receivable, net			$	1,053,758					$	974,535

Billed accounts receivable represent amounts billed to clients that have not been collected. Unbilled accounts receivable, which represent an unconditional right to payment subject only to the passage of time, include unbilled amounts typically resulting from revenue recognized but not yet billed pursuant to contract terms or billed after the period end date. Substantially all of our unbilled receivables at June 30, 2024 are expected to be billed and collected within 12 months. The allowance for doubtful accounts represents amounts that are expected to become uncollectible or unrealizable in the future. We determine an estimated allowance for uncollectible accounts based on management's consideration of trends in the actual and forecasted credit quality of our clients, including delinquency and payment history; type of client, such as a government agency or a commercial sector client; and general economic and industry conditions, which may affect our clients' ability to pay.

Other than the U.S. federal government, no single client accounted for more than 10% of our accounts receivable at June 30, 2024 and October 1, 2023.

Remaining Unsatisfied Performance Obligation (“RUPO”)

Our RUPO represents a measure of the total dollar value of work to be performed on contracts awarded and in progress. We had $5.2 billion of RUPO at June 30, 2024. Our RUPO increases with awards from new contracts or additions on existing contracts, and decreases as work is performed and revenue is recognized on existing contracts. Our RUPO may also decrease when projects are canceled or modified in scope. We include a contract within our RUPO when the contract is awarded and an agreement on contract terms has been reached.

We expect to satisfy our RUPO at June 30, 2024 over the following periods (in thousands):

			Amount
Within 12 months			$	3,508,571
Beyond			1,683,295
Total			$	5,191,866

Although RUPO reflects business that is considered to be firm, cancellations, deferrals or scope adjustments may occur. Our RUPO is adjusted to reflect any known project cancellations, revisions to project scope and cost, foreign currency

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exchange fluctuations and project deferrals, as appropriate. Our operations and maintenance contracts can generally be terminated by the clients without a substantive financial penalty; therefore, the remaining performance obligations on such contracts are limited to the notice period required for the termination (usually 30, 60, or 90 days).

In the second quarter of fiscal 2024, we acquired LS Technologies ("LST"), an innovative U.S. federal enterprise technology services and management consulting firm based in Fairfax, Virginia. LST provides high-end consulting and engineering services including advanced data analytics, cybersecurity and digital transformation solutions to U.S. government clients. In the third quarter of fiscal 2024, we also acquired Convergence Controls & Engineering ("CCE"), an industry leader in process automation and systems integration solutions. CCE’s expertise includes customized digital controls and software solutions, advanced data analytics, cloud data integration, and cybersecurity applications. Both LST and CCE are included in our Government Services Group ("GSG") segment. The aggregate fair value of the purchase price of these two acquisitions was $120 million. This amount consisted of $93 million in initial cash payments, $4 million of cash holdback related to a tax reserve, and $23 million for the estimated fair value of contingent earn-out obligations, with a maximum of $60 million, based upon the achievement of specified operating income targets in each of the three years following the acquisition dates. The $120 million purchase price was allocated $12 million to net tangible assets, $23 million to identifiable intangible assets, and $85 million to goodwill. The purchase price allocation is preliminary and subject to adjustment as the estimates, assumptions, valuations and other analyses have not yet been finalized in order to make a definitive allocation. These acquisitions were not considered material, individually or in aggregate, to our consolidated financial statements. As a result, no pro forma information has been provided.

On September 23, 2022, we made an all cash offer to acquire all the outstanding shares of RPS Group plc ("RPS"), a publicly traded company on the London Stock Exchange for 222 pence per share, through a scheme of arrangement, which was unanimously recommended by RPS' Board of Directors. On November 3, 2022, RPS' shareholders approved the scheme of arrangement. On January 19, 2023, the court-sanctioned scheme of arrangement to purchase RPS was approved, and we completed the acquisition on January 23, 2023. RPS employs approximately 5,000 associates in the United Kingdom, Europe, Asia Pacific and North America, delivering high-end solutions, especially in energy transformation, water and program management for government and commercial clients. Substantially all of RPS is included in our Commercial/International Services Group ("CIG") segment.

The total purchase price for RPS was approximately £633 million ($784 million). In the third quarter and first nine months of fiscal 2023, we incurred $2.1 million and $25.8 million, respectively, of acquisition and integration costs primarily for professional fees, substantially all of which were paid as of the end of the third quarter of fiscal 2023. On January 23, 2023, we also settled a foreign exchange forward contract that was integral to our plan to finance the RPS acquisition. The cash gain of $109.3 million did not qualify for hedge accounting. As a result, the gain was recognized as non-operating income over the life of the contract and not included in the purchase price allocation below. However, the cash proceeds of $109.3 million economically reduced the purchase price for the shares of RPS to approximately $675 million. This forward contract is explained further in Note 16, "Derivative Financial Instruments".

The table below represents the purchase price allocation for RPS based on estimates, assumptions, valuations and other analyses as of January 23, 2023. The all cash purchase consideration, excluding the aforementioned forward contract gain, was allocated to the tangible and intangible assets, and liabilities of RPS based on their estimated fair values, with any excess purchase consideration allocated to goodwill as follows (in thousands):

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			Amount
Cash and cash equivalents			$	32,093
Accounts receivable and contract assets			202,303
Prepaid expenses and other current assets			45,999
Income taxes receivables			1,999
Property and equipment			38,435
Right-of-use assets, operating leases			40,179
Intangible assets			174,094
Deferred income taxes			35,084
Other long-term assets			1,061
Total assets acquired			571,247
Accounts payable			$	(44,376)
Accrued compensation			(19,073)
Contract liabilities			(46,287)
Income tax payable			(7,083)
Short-term lease liabilities, operating leases			(13,477)
Other current liabilities			(135,474)
Current portion of long-term debt			(91,973)
Long-term lease liabilities, operating leases			(26,702)
Other long-term liabilities			(13,742)
Deferred tax liabilities			(41,613)
Total liabilities assumed			(439,800)
Fair value of net assets acquired			131,447
Goodwill			652,762
Total purchase consideration			$	784,209

The following table summarizes the estimated fair values that were assigned to intangible assets at the acquisition date:

			Fair Value						Weighted-Average Estimated Useful Life
			(in thousands)						(in years)
Backlog			$	27,880					1.6
Trade names			27,260						3.0
Client relations			118,954						11.1
Total intangible assets acquired			$	174,094					8.3

Estimated fair value measurements for the intangible assets related to the RPS acquisition were made using Level 3 inputs including discounted cash flow techniques. Fair value was estimated using a multi-period excess earnings method for backlog and client relations and a relief from royalty method for trade names. The significant assumptions used in estimating fair value of backlog and client relations include (i) the estimated life the asset will contribute to cash flows, such as remaining contractual terms, (ii) revenue growth rates and EBITDA margins, (iii) attrition rate of customers, and (iv) the estimated discount rates that reflect the level of risk associated with receiving future cash flows. The significant assumptions used in estimating fair value of trade names include the royalty rates and discount rates.

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Supplemental Pro Forma Information (Unaudited)

Following are the supplemental consolidated financial results of Tetra Tech and RPS for the third quarter and first nine months of fiscal 2023 on an unaudited pro forma basis, as if the RPS acquisition had been consummated at the beginning of fiscal 2023 (in thousands):

			Three Months Ended						Nine Months Ended
			July 2, 2023						July 2, 2023
Revenue			$	1,208,947					$	3,519,792
Net income including noncontrolling interests			61,770						104,564

In fiscal 2023, we also acquired Amyx, Inc. (“Amyx”), an enterprise technology services, cybersecurity and management consulting firm based in Reston, Virginia. With over 500 employees, Amyx provides application modernization, cybersecurity, systems engineering, financial management and program management support on over 30 Federal Government programs. Amyx is included in our GSG segment. The total fair value of the purchase price of Amyx was $120.9 million, consisted of a $100.0 million payable in a promissory note issued to the sellers (paid subsequent to closing), $8.7 million of payables related to estimated post-closing adjustments, and $12.2 million for the estimated fair value of contingent earn-out obligations, with a maximum of $25.0 million, based upon the achievement of specified operating income targets in each of the three years following the acquisition date. Amyx was not considered material to our consolidated financial statements. As a result, no pro forma information has been provided.

The fiscal 2024 goodwill addition from LST and CCE are deductible for tax purposes, while the majority of the goodwill from the fiscal 2023 acquisitions is not deductible for tax purposes. The results of fiscal 2024 and 2023 acquisitions were included in our consolidated financial statements beginning on their respective closing dates.

Our fiscal 2024 goodwill additions from the LST and CCE acquisitions reflect the extensive technical knowledge of the acquired workforces, the anticipated synergies in data analytics, cybersecurity and digital transformation services, and collective reputations of these acquisitions in providing mission critical solutions to both commercial and government customers. The goodwill additions from fiscal 2023 business combinations are primarily attributable to the significant technical expertise residing in embedded workforces that are sought out by clients, synergies expected to arise after the acquisitions in the areas of enterprise technology services, data management, energy transformation, water, program management, and data analytics and the long-standing reputations of RPS and Amyx. These acquisitions further expand and complement our market-leading positions in water and environment; enhanced by a combined suite of differentiated data analytics and digital technologies, and expansion into existing and new geographies.

Intangible assets with finite lives arise from business acquisitions and are amortized based on the period over which the contractual or economic benefit of the intangible assets are expected to be realized on a straight-line basis over the useful lives of the underlying assets, ranging from one to 12 years. These consist of client relations, backlog and trade names. For detailed information regarding our intangible assets, see Note 5, “Goodwill and Intangible Assets”.

Most of our acquisition agreements include contingent earn-out agreements, which are generally based on the achievement of future operating income thresholds. The contingent earn-out arrangements are based on our valuations of the acquired companies and reduce the risk of overpaying for acquisitions if the projected financial results are not achieved. The fair values of any earn-out arrangements are included as part of the purchase price of the acquired companies on their respective acquisition dates. For each transaction, we estimate the fair value of contingent earn-out payments as part of the initial purchase price and record the estimated fair value of contingent consideration as a liability in “Current contingent earn-out liabilities” and “Non-current contingent earn-out liabilities” on the consolidated balance sheets. We consider several factors when determining that contingent earn-out liabilities are part of the purchase price, including the following: (1) the valuation of our acquisitions is not supported solely by the initial consideration paid, and the contingent earn-out formula is a critical and material component of the valuation approach to determining the purchase price; and (2) the former owners of acquired companies that remain as key employees receive compensation other than contingent earn-out payments at a reasonable level compared with the compensation of our other key employees. The contingent earn-out payments are not affected by employment termination.

We measure our contingent earn-out liabilities at fair value on a recurring basis using significant unobservable inputs classified within Level 3 of the fair value hierarchy. We use a probability-weighted discounted income approach as a valuation technique to convert future estimated cash flows to a single present value amount. The significant unobservable inputs used in

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the fair value measurements are operating income projections over the earn-out period (generally three to five years), and the probability outcome percentages we assign to each scenario. Significant increases or decreases to either of these inputs in isolation would result in a significantly higher or lower liability, with a higher liability capped by the contractual maximum of the contingent earn-out obligation. Ultimately, the liability will be equivalent to the amount paid, and the difference between the fair value estimate and amount paid will be recorded in earnings. The amount paid that is less than or equal to the contingent earn-out liability on the acquisition date is reflected as cash used in financing activities in our consolidated statements of cash flows. Any amount paid in excess of the contingent earn-out liability on the acquisition date is reflected as cash used in operating activities in our consolidated statements of cash flows.

We review and reassess the estimated fair value of contingent consideration on a quarterly basis, and the updated fair value could differ materially from the initial estimates. Changes in the estimated fair value of our contingent earn-out liabilities related to the time component of the present value calculation are reported in interest expense. Adjustments to the estimated fair value related to changes in all other unobservable inputs are reported in operating income. In the first nine months of fiscal 2024, we evaluated our estimates for contingent consideration liabilities for the remaining earn-out periods for each individual acquisition, which included a review of their financial results to-date, the status of ongoing projects in their RUPO, and the inventory of prospective new contract awards.

During the third quarter and first nine months of fiscal 2024, we recorded immaterial adjustments, individually and in aggregate, to our contingent earn-out liabilities and included the corresponding amount in our operating income. During the first nine months of fiscal 2023, we recorded adjustments to our contingent earn-out liabilities and reported a related net loss in operating income of $8.5 million (largely in the second quarter). The net loss primarily resulted from increased valuation of the contingent consideration liabilities for our prior acquisitions of Segue Technologies, Inc., Hoare Lea, LLP and The Integration Group of Americas, Inc., reflecting financial performance that exceeded our previous expectations.

The following table summarizes the changes in the fair value of estimated contingent consideration (in thousands):

			Three Months Ended												Nine Months Ended
			June 30, 2024						July 2, 2023						June 30, 2024						July 2, 2023
Beginning balance			$	74,579					$	88,082					$	73,422					$	65,566
Estimated earn-out liabilities for acquisitions			1,138						—						23,038						12,248
Payments of contingent consideration			(7,000)						(13,078)						(29,112)						(15,078)
Adjustments to fair value recorded in earnings			500						—						477						8,477
Interest accretion expense			1,038						707						1,953						1,919
Effect of foreign currency exchange rate changes			28						888						505						3,467
Ending balance			$	70,283					$	76,599					$	70,283					$	76,599
Maximum potential payout at end of period			$	128,573					$	120,320					$	128,573					$	120,320

The following table summarizes the changes in the carrying value of goodwill by reportable segment (in thousands):

						GSG						CIG						Total
Balance at October 1, 2023						$	659,942					$	1,220,302					$	1,880,244
Acquisition activity						84,865						—						84,865
Translation and other adjustments						2,282						24,719						27,001
Balance at June 30, 2024						$	747,089					$	1,245,021					$	1,992,110

The goodwill addition in GSG resulted from the purchase price allocations for our fiscal 2024 acquisitions which are preliminary and subject to adjustment based upon the final determinations of the net assets acquired and information to perform the final valuation. Goodwill adjustments primarily related to the foreign currency translation adjustments which resulted from our foreign subsidiaries with functional currencies that are different than our reporting currency. These goodwill amounts are presented net of reductions from historical impairment adjustments. The gross amounts for GSG were $764.8 million and $677.6 million at June 30, 2024 and October 1, 2023, respectively, excluding accumulated impairment of $17.7 million at each

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date. The gross amounts of goodwill for CIG were $1,366.5 million and $1,341.8 million at June 30, 2024 and October 1, 2023, respectively, excluding accumulated impairment of $121.5 million at each date.

We perform our annual goodwill impairment review at the beginning of our fiscal fourth quarter. Our most recent annual review at July 3, 2023 (i.e. the first day of our fourth quarter in fiscal 2023) indicated that we had no impairment of goodwill, and all of our reporting units had estimated fair values that were in excess of their carrying values, including goodwill. At July 3, 2023, we had no reporting units that had estimated fair values that exceeded their carrying values by less than 45%.

We also regularly evaluate whether events and circumstances have occurred that may indicate a potential change in the recoverability of goodwill. We perform interim goodwill impairment reviews between our annual reviews if certain events and circumstances have occurred, such as a deterioration in general economic conditions; an increase in the competitive environment; a change in management, key personnel, strategy or customers; negative or declining cash flows; or a decline in actual or planned revenue or earnings compared with actual and projected results of relevant prior periods. Although we believe that our estimates of fair value for these reporting units are reasonable, if financial performance for these reporting units falls significantly below our expectations or market prices for similar business decline, the goodwill for these reporting units could become impaired.

The following table presents the gross amount and accumulated amortization of our acquired identifiable intangible assets with finite useful lives included in “Intangible assets, net” on the consolidated balance sheets ($ in thousands):

			Period Ended
			June 30, 2024																								October 1, 2023
			Weighted- Average Remaining Life (in Years)						Gross Amount						Accumulated Amortization						Net Amount						Gross Amount						Accumulated Amortization						Net Amount
Client relations			8.4						$	190,329					$	(50,980)					$	139,349					$	169,217					$	(36,072)					$	133,145
Backlog			0.6						72,579						(65,050)						7,529						63,825						(47,802)						16,023
Trade names			1.7						38,773						(21,192)						17,581						37,411						(12,643)						24,768
Total									$	301,681					$	(137,222)					$	164,459					$	270,453					$	(96,517)					$	173,936

Amortization expense for the third quarter and first nine months of fiscal 2024 was $13.8 million and $38.4 million, compared to $14.1 million and $29.6 million, respectively, for the prior-year periods. Estimated amortization expense for the remainder of fiscal 2024 and succeeding years is as follows (in thousands):

			Amount
2024 (remaining)			$	11,322
2025			34,712
2026			23,334
2027			16,830
2028			16,320
Beyond			61,941
Total			$	164,459

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Property and equipment consisted of the following (in thousands):

			Balance at
			June 30, 2024						October 1, 2023
Equipment, furniture and fixtures			$	130,748					$	132,744
Leasehold improvements			46,042						44,733
Total property and equipment			176,790						177,477
Accumulated depreciation			(106,096)						(102,645)
Property and equipment, net			$	70,694					$	74,832

For the third quarter and first nine months of fiscal 2024, our depreciation expense related to property and equipment was $5.7 million and $18.3 million, respectively, compared to $5.6 million and $13.7 million for third quarter and first nine months of fiscal 2023, respectively.

On October 5, 2021, our Board of Directors authorized a new stock repurchase program under which we could repurchase up to $400 million of our common stock. We did not repurchase any shares of our common stock in the first nine months of fiscal 2024 and 2023. At June 30, 2024, we had a remaining balance of $347.8 million under our stock repurchase program.

The following table presents dividends declared and paid in the first nine months of fiscal 2024 and 2023:

Declare Date						Dividend Paid Per Share						Record Date						Payment Date						Dividend Paid (in thousands)
November 13, 2023						$	0.26					November 30, 2023						December 13, 2023						$	13,873
January 29, 2024						0.26						February 14, 2024						February 27, 2024						13,908
April 29, 2024						0.29						May 20, 2024						May 31, 2024						15,522
Total dividend paid as of June 30, 2024																								$	43,303
November 7, 2022						$	0.23					November 21, 2022						December 9, 2022						$	12,186
January 30, 2023						0.23						February 13, 2023						February 24, 2023						12,242
May 8, 2023						0.26						May 24, 2023						June 6, 2023						13,840
Total dividend paid as of July 2, 2023																								$	38,268

Our operating leases are primarily for corporate and project office spaces. To a much lesser extent, we have operating leases for vehicles and equipment. Our operating leases have remaining lease terms of one month to ten years, some of which may include options to extend the leases for up to five years.

We determine if an arrangement is a lease at inception. Operating leases are included in "Right-of-use assets, operating leases", "Short-term lease liabilities, operating leases" and "Long-term lease liabilities, operating leases" in the consolidated balance sheets. Our finance leases are primarily for certain IT equipment and are immaterial.

Right-of-use ("ROU") assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. As most of our leases do not provide an implicit rate, incremental borrowing rates are used based on the information available at commencement date in determining the present value of lease payments. The operating lease ROU asset at the commencement date also includes any lease payments made to the lessor at or before the commencement date and initial direct costs less lease incentives received. Lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. Lease expense for operating lease payments is recognized on a straight-line basis over the lease term.

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The components of lease costs are as follows (in thousands):

			Three Months Ended												Nine Months Ended
			June 30, 2024						July 2, 2023						June 30, 2024						July 2, 2023
Operating lease cost			$	24,562					$	24,775					$	73,580					$	70,155
Sublease income			(184)						(46)						(347)						(125)
Total lease cost			$	24,378					$	24,729					$	73,233					$	70,030

Supplemental cash flow information related to leases is as follows (in thousands):

						Nine Months Ended
						June 30, 2024						July 2, 2023
Operating cash flows for operating leases						$	56,379					$	57,871
Right-of-use assets obtained in exchange for new operating lease liabilities						38,160						72,294

Supplemental balance sheet and other information related to leases are as follows (in thousands):

			Balance at
			June 30, 2024						October 1, 2023
Operating leases:
Right-of-use assets			$	167,317					$	175,932
Lease liabilities:
Current			65,932						65,005
Non-current			128,892						144,685
Total operating lease liabilities			$	194,824					$	209,690
Weighted-average remaining lease term:
Operating leases			4 years						5 years
Weighted-average discount rate:
Operating leases			3.4		%				3.0		%

At June 30, 2024, we had $13.9 million of operating leases that have not yet commenced.

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A maturity analysis of the future undiscounted cash flows associated with our lease liabilities at June 30, 2024 is as follows (in thousands):

			Operating Leases
2024 (remaining)			$	20,124
2025			65,068
2026			44,638
2027			31,231
2028			20,176
Beyond			28,412
Total lease payments			209,649
Less: imputed interest			(14,825)
Total present value of lease liabilities			$	194,824

In fiscal 2020, the Canadian federal government implemented the Canadian Emergency Wage Subsidy ("CEWS") program in response to the negative impact of the coronavirus disease 2019 pandemic on businesses operating in Canada. Some of our Canadian legal entities qualified for and applied for these CEWS cash benefits to partially offset the impacts of revenue reductions and on-going staffing costs. The $21 million total received was initially recorded in "Other long-term liabilities" until all potential amendments to the qualification criteria, including some that were proposed with retroactive application, were finalized in fiscal 2022. In the first nine months of fiscal 2024 (all in the first quarter of fiscal 2024), we distributed approximately $10 million to our Canadian employees. The remaining $11 million, which we expect to distribute within one year, is reported in "Accrued compensation". We do not expect there will be any related impact on our operating income, and we have no outstanding applications for further government assistance.

We recognize the fair value of our stock-based awards as compensation expense on a straight-line basis over the requisite service period in which the award vests. Stock-based compensation expense for the three and nine months ended June 30, 2024 was $8.1 million and $23.7 million, compared to $7.0 million and $21.6 million for the same periods last year. Most of these amounts were included in selling, general and administrative expenses on our consolidated statements of income. In the first nine months of fiscal 2024, we awarded 55,836 performance share units (“PSUs”) to our non-employee directors and executive officers at an estimated fair value of $203.53 per share on the award date. All PSUs are performance-based and vest, if at all, after the conclusion of the three-year performance period. The number of PSUs that ultimately vest is based 50% on the growth in our diluted earnings per share and 50% on our relative total shareholder return over the vesting period. Additionally, we awarded 141,880 restricted stock units (“RSUs”) to our non-employee directors, executive officers and employees at a fair value of $164.78 per share on the award date. All executive officer and employee RSUs have time-based vesting over a four-year period, and the non-employee director RSUs vest after one year.

Basic EPS is computed by dividing net income available to common stockholders by the weighted-average number of common shares outstanding, less unvested restricted stock for the period. Diluted EPS is computed by dividing net income by the weighted-average number of common shares outstanding and dilutive potential common shares for the period. Potential common shares include the weighted-average dilutive effects of stock-based awards and shares underlying our Convertible Senior Notes (the "Convertible Notes").

For the third quarter and first nine months of fiscal 2024, our Convertible Notes, described in Note 15, "Long-Term Debt", had a dilution impact on the dilutive potential common shares, which was calculated using the if-converted method. The dilution impact was due to the price of our common stock exceeding the conversion price. The related capped call transactions (the "Capped Call Transactions") were excluded from the calculation of dilutive potential common shares as their effect is anti-dilutive. For the third quarters and first nine months of fiscal 2024 and 2023, no options were excluded from the calculation of dilutive potential common shares.

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The following table presents the number of weighted-average shares used to compute basic and diluted EPS (in thousands, except per share data):

			Three Months Ended												Nine Months Ended
			June 30, 2024						July 2, 2023						June 30, 2024						July 2, 2023
Net income attributable to Tetra Tech			$	85,810					$	60,235					$	237,228					$	219,771
Weighted-average common shares outstanding – basic			53,515						53,231						53,451						53,188
Effect of dilutive stock options and unvested restricted stock			433						422						415						427
Shares issuable assuming conversion of convertible notes			104						—						35						—
Weighted-average common shares outstanding – diluted			54,052						53,653						53,901						53,615
Earnings per share attributable to Tetra Tech:
Basic			$	1.60					$	1.13					$	4.44					$	4.13
Diluted			$	1.59					$	1.12					$	4.40					$	4.10

The effective tax rates for the first nine months of fiscal 2024 and 2023 were 27.7% and 28.3%, respectively. Income tax expense was reduced by $2.9 million and $2.2 million of excess tax benefits on share-based payments in the first nine months of fiscal 2024 and 2023, respectively. In addition, income tax expense in the first nine months of fiscal 2024 included $4.3 million of expense for the settlement of various tax positions that were under audit for fiscal years 2018 through 2021. Furthermore, income tax expense in the first nine months of fiscal 2023 included non-operating income tax expenses of $7.2 million ($6.9 million in the second quarter) to recognize the tax liability for foreign earnings, primarily in the United Kingdom and Australia, that are no longer indefinitely reinvested and to increase the liability for an uncertain tax position. Excluding the impact of the excess tax benefits on share-based payments, the settlement amounts in the first nine months of fiscal 2024 and the additional $7.2 million in the first nine months of fiscal 2023, our effective tax rates in the first nine months of fiscal 2024 and 2023 were 27.2% and 26.7%, respectively.

At June 30, 2024 and October 1, 2023, the liability for income taxes associated with uncertain tax positions was $64.0 million and $62.0 million, respectively. It is reasonably possible that the liabilities with respect to certain of our unrecognized tax positions may significantly decrease in the next 12 months. These changes would be the result of ongoing examinations. These liabilities represent our current estimates of the additional tax liabilities that we may be assessed when the related audits are concluded. If these audits are resolved in a manner more unfavorable than our current expectations, our tax liabilities could be materially higher than the amounts currently recorded resulting in additional tax expense.

We manage our operations under two reportable segments. Our GSG reportable segment primarily includes activities with U.S. government clients (federal, state and local) and all activities with development agencies worldwide. Our CIG reportable segment primarily includes activities with U.S. commercial clients and international clients other than development agencies.

GSG provides high-end consulting and engineering services primarily to U.S. government clients (federal, state and local) and international development agencies worldwide. GSG supports U.S. government civilian and defense agencies with services in water, environment, sustainable infrastructure, information technology and disaster management. GSG also provides engineering design services for U.S. based federal and municipal clients, especially in water infrastructure, flood protection and solid waste. GSG also leads our support for development agencies worldwide, especially in the United States, United Kingdom and Australia.

CIG primarily provides high-end consulting and engineering services to U.S. commercial clients, and international clients inclusive of the commercial and government sectors. CIG supports commercial clients worldwide in renewable energy,

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industrial, high performance buildings and aerospace markets. CIG also provides sustainable infrastructure and related environmental, engineering and project management services to commercial and local government clients across Canada, in Asia Pacific (primarily Australia and New Zealand), Europe, the United Kingdom and South America (primarily Brazil).

Management evaluates the performance of these reportable segments based upon their respective segment operating income before the effect of amortization expense related to acquisitions, and other unallocated corporate expenses. We account for inter-segment revenues and transfers as if they were to third parties; that is, by applying a negotiated fee onto the costs of the services performed. All significant intercompany balances and transactions are eliminated in consolidation. In the third quarter and first nine months of fiscal 2023, our Corporate segment operating losses included $2.1 million and $25.8 million of acquisition and integration expenses, respectively, as described in Note 4, “Acquisitions”.

The following tables summarize financial information regarding our reportable segments (in thousands):

			Three Months Ended												Nine Months Ended
			June 30, 2024						July 2, 2023						June 30, 2024						July 2, 2023
Revenue
GSG			$	640,553					$	531,050					$	1,812,721					$	1,565,371
CIG			723,617						691,386						2,063,879						1,741,300
Elimination of inter-segment revenue			(19,847)						(13,489)						(52,395)						(44,733)
Total revenue			$	1,344,323					$	1,208,947					$	3,824,205					$	3,261,938
Income from operations
GSG			$	71,518					$	54,496					$	198,652					$	167,053
CIG			86,465						69,572						233,821						172,199
Corporate (1)			(29,353)						(26,393)						(75,078)						(88,516)
Total income from operations			$	128,630					$	97,675					$	357,395					$	250,736

(1)     Includes amortization of intangibles, acquisition and integration expenses, as well as other costs and other income not allocable to our reportable segments.

			Balance at
			June 30, 2024						October 1, 2023
Total Assets
GSG			$	632,346					$	543,066
CIG			1,066,241						994,470
Corporate (1)			2,386,318						2,282,941
Total assets			$	4,084,905					$	3,820,477

(1)    Corporate assets consist of intercompany eliminations and assets not allocated to our reportable segments including goodwill, intangible assets, deferred income taxes and certain other assets.

We classified our assets and liabilities that were carried at fair value in one of the following categories:

•Level 1: Quoted market prices in active markets for identical assets or liabilities.

•Level 2: Observable market-based inputs or unobservable inputs that are corroborated by market data.

•Level 3: Unobservable inputs that are not corroborated by market data.

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Derivative Instruments. Our derivative instruments are categorized within Level 2 of the fair value hierarchy. For additional information about our derivative financial instruments (see Note 16, "Derivative Financial Instruments").

Contingent Consideration. We measure our contingent earn-out liabilities at fair value on a recurring basis using significant unobservable inputs classified within Level 3 of the fair value hierarchy. (see Note 4, "Acquisitions" for further information).

Debt. The fair value of long-term debt under our Credit Facility was determined using the present value of future cash flows based on the borrowing rates currently available for debt with similar terms and maturities (Level 2 measurement, as described in “Critical Accounting Policies and Estimates” in our Annual Report on Form 10-K for the fiscal year ended October 1, 2023). The carrying value of our long-term debt under our Credit Facility approximated fair value at June 30, 2024 and October 1, 2023. At June 30, 2024, we had $300 million in outstanding borrowings under the Amended Credit Agreement, which was consisted of $300 million under the New Term Loan Facility and no borrowings under the Amended Revolving Credit Facility.

The estimated fair value of our $575 million Convertible Notes was determined based on the trading price of the Convertible Notes as of the last trading day of our third quarter of fiscal 2024. We consider the fair value of the Convertible Notes to be a Level 2 measurement as they are not actively traded in markets. The carrying amounts and estimated fair values of the Convertible Notes were approximately $563 million and $674 million, respectively, at June 30, 2024, and $561 million and $566 million, respectively, at October 1, 2023.

Long-term debt consisted of the following (in thousands):

			Balance at
			June 30, 2024						October 1, 2023
Credit facilities			$	300,000					$	320,000
Convertible notes			575,000						575,000
Debt issuance costs and discount			(13,170)						(15,471)
Long-term debt			$	861,830					$	879,529

On August 22, 2023, we issued $575.0 million in Convertible Notes that bear interest at a rate of 2.25% per annum payable in arrears on February 15 and August 15 of each year, beginning on February 15, 2024, and mature on August 15, 2028, unless converted, redeemed or repurchased. Prior to May 15, 2028, the Convertible Notes will be convertible at the option of the holders only upon the occurrence of certain events and during certain periods. Thereafter, the Convertible Notes will be convertible at the option of the holders at any time until the close of business on the second scheduled trading day immediately preceding the maturity date.

The initial conversion rate applicable to the Convertible Notes was 5.0855 shares of our common stock per $1,000 principal amount of the Convertible Notes, which was equivalent to an initial price of approximately $196.64 per share of our common stock. The conversion rate is subject to adjustment for certain events, including stock splits and issuance of certain stock dividends on our common stock. At June 30, 2024, the applicable conversion rate was 5.0862 shares of common stock per $1,000 principal amount of the Convertible Notes (equivalent to an adjusted conversion price of approximately $196.61 per share of common stock). Upon conversion, we will pay cash up to the aggregate principal amount of the Convertible Notes to be converted and pay or deliver, as the case may be, cash, shares of our common stock or a combination of cash and shares of our common stock, at our election, in respect of the remainder, if any, of our conversion obligation in excess of the aggregate principal amount of the Convertible Notes being converted. In addition, upon the occurrence of a "fundamental change" as defined in the indenture governing the Convertible Notes, holders may require us to repurchase for cash all or any portion of their Convertible Notes at a fundamental change repurchase price equal to 100% of the principal amount of the Convertible Notes to be repurchased plus any accrued and unpaid interest. If certain corporate events occur prior to the maturity date of the Convertible Notes or if we deliver a notice of redemption, we will, in certain circumstances, increase the conversion rate for a holder who elects to convert its Convertible Notes in connection with such event or notice of redemption.

We will not be able to redeem the Convertible Notes prior to August 20, 2026. On or after August 20, 2026, we have the option to redeem for cash all or any portion of the Convertible Notes if the last reported sale price of our common stock is

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equal to or greater than 130% of the conversion price for a specified period of time at a redemption price equal to 100% of the principal amount of the Convertible Notes to be redeemed, plus any accrued but unpaid interest. In addition, as described in the indenture governing the Convertible Notes, certain events of default including, but not limited to, bankruptcy, insolvency or reorganization, may result in the Convertible Notes becoming due and payable immediately.

Our net proceeds from the offering were approximately $560.5 million after deducting the initial purchasers’ discounts and commissions and offering expenses. We used approximately $51.8 million of the net proceeds to pay the cost of the Capped Call Transactions described below. We used the remaining net proceeds to repay all $185.0 million principal amount outstanding under our revolving credit facility, the remaining $234.4 million principal amount outstanding under our senior secured term loan due 2027 and approximately $89.4 million principal amount outstanding under our senior secured term loan due 2026.

The Convertible Notes were recorded as a single unit within "Long-term debt" in our consolidated balance sheets as the conversion option within the Convertible Notes was not a derivative that would require bifurcation and the Convertible Notes did not involve a substantial premium. Transaction costs to issue the Convertible Notes were recorded as direct deductions from the related debt liabilities and are amortized to interest expense using the effective interest method over the terms of the Convertible Notes resulting in an effective annual interest rate of 2.79%.

The net carrying amount of the Convertible Notes was as follows (in thousands):

			Balance at
			June 30, 2024						October 1, 2023
Principal			$	575,000					$	575,000
Unamortized discount and issuance costs			(12,118)						(14,158)
Net carrying amount			$	562,882					$	560,842

The following table sets forth the interest expense recognized related to the Convertible Notes for the third quarter and first nine months of fiscal 2024 (in thousands):

			Three Months Ended						Nine Months Ended
			June 30, 2024						June 30, 2024
Interest expense			$	3,234					$	9,631
Amortization of discount and issuance costs			680						2,040
Total interest expense			$	3,914					$	11,671

Concurrent with the offering of the Convertible Notes, in August 2023, we entered into the Capped Call Transactions. The Capped Call Transactions are expected generally to reduce the potential dilution of our common stock upon conversion of the Convertible Notes and/or offset any cash payments we elect to make in excess of the principal amount of converted Convertible Notes, as the case may be. If, however, the market price per share of our common stock, as measured under the terms of the Capped Call Transactions, exceeds the cap price of the Capped Call Transactions, there would nevertheless be dilution and/or there would not be an offset of such cash payments, in each case, to the extent that such market price exceeds the cap price of the Capped Call Transactions. The cap price of the Capped Call Transactions was initially $259.56 per share, which represented a premium of 65% over the last reported sale price of our common stock of $157.31 per share on the NASDAQ Global Select Market on August 17, 2023. The cap price is subject to adjustment for certain events, including stock splits and issuance of certain stock dividends on our common stock. At June 30, 2024, the adjusted cap price was approximately $259.53 per share. We recorded the Capped Call Transactions as separate transactions from the issuance of the Convertible Notes. The cost of $51.8 million incurred to purchase the Capped Call Transactions was recorded as a reduction to additional paid-in capital (net of $12.9 million in deferred taxes) on our consolidated balance sheet as of fiscal 2023 year-end.

On October 26, 2022, we entered into a Third Amended and Restated Credit Agreement that provides for an additional $500 million senior secured term loan facility (the "New Term Loan Facility") increasing our total borrowing capacity to $1.55 billion. On January 23, 2023, we drew the entire amount of the New Term Loan Facility to partially finance the RPS

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acquisition. The New Term Loan Facility is not subject to any amortization payments of principal and matures on the third anniversary of the RPS acquisition closing date in January 2026.

On February 18, 2022, we entered into Amendment No. 2 to Second Amended and Restated Credit Agreement (“Amended Credit Agreement”) with a total borrowing capacity of $1.05 billion that will mature in February 2027. The Amended Credit Agreement is a $750 million senior secured, five-year facility that provides for a $250 million term loan facility (the “Amended Term Loan Facility”) and a $500 million revolving credit facility (the “Amended Revolving Credit Facility”). In addition, the Amended Credit Agreement includes a $300 million accordion feature that allows us to increase the Amended Credit Agreement to $1.05 billion subject to lender approval. The Amended Credit Agreement provides for, among other things, (i) refinance indebtedness under our Credit Agreement dated at July 30, 2018; (ii) finance open market repurchases of common stock, acquisitions, and cash dividends and distributions; and (iii) utilize the proceeds for working capital, capital expenditures and other general corporate purposes. The Amended Credit Agreement provides for a reduction in the interest grid for meeting certain sustainability targets related to the (i) reduction of greenhouse gas emissions through the Company’s projects and operational sustainability initiatives and (ii) improvement of peoples’ lives as a result of the Company’s projects that provide environmental, social and governance benefits. The Amended Revolving Credit Facility includes a $100 million sublimit for the issuance of standby letters of credit, a $20 million sublimit for swingline loans and a $300 million sublimit for multicurrency borrowings and letters of credit.

The entire Amended Term Loan Facility was drawn on February 18, 2022. We may borrow on the Amended Revolving Credit Facility, at our option, at either (a) a benchmark rate plus a margin that ranges from 1.000% to 1.875% per annum, or (b) a base rate for loans in U.S. dollars (the highest of the U.S. federal funds rate plus 0.50% per annum, the bank’s prime rate or the Secured Overnight Financing Rate ("SOFR") rate plus 1.00%, plus a margin that ranges from 0% to 0.875% per annum. In each case, the applicable margin is based on our Consolidated Leverage Ratio, calculated quarterly. The Amended Term Loan Facility is subject to the same interest rate provisions. The Amended Credit Agreement expires on February 18, 2027, or earlier at our discretion upon payment in full of loans and other obligations.

At June 30, 2024, we had $300 million in outstanding borrowings under the Amended Credit Agreement, which was consisted of $300 million under the New Term Loan Facility and no borrowings under the Amended Revolving Credit Facility. During the nine months ended June 30, 2024, the weighted-average interest rate of the outstanding borrowings under the Amended Credit Agreement was 6.72%. In addition, we had $0.7 million in standby letters of credit under the Amended Credit Agreement. At June 30, 2024, we had $499.3 million of available credit under the Amended Revolving Credit Facility, all of which could be borrowed without a violation of our debt covenants.

The Amended Credit Agreement contains certain affirmative and restrictive covenants, and customary events of default. The financial covenants provide for a maximum Consolidated Leverage Ratio of 3.25 to 1.00 (total funded debt/EBITDA, as defined in the Amended Credit Agreement) and a minimum Consolidated Interest Coverage Ratio of 3.00 to 1.00 (EBITDA/Consolidated Interest Charges, as defined in the Amended Credit Agreement). Our obligations under the Amended Credit Agreement are guaranteed by certain of our domestic subsidiaries and are secured by first priority liens on (i) the equity interests of certain of our subsidiaries, including those subsidiaries that are guarantors or borrowers under the Amended Credit Agreement, and (ii) the accounts receivable, general intangibles and intercompany loans and those of our subsidiaries that are guarantors or borrowers. At June 30, 2024, we were in compliance with these covenants with a consolidated leverage ratio of 1.51x and a consolidated interest coverage ratio of 12.47x.

In addition to the Amended Credit Agreement, we maintain other credit facilities, which may be used for short-term cash advances and bank guarantees. At June 30, 2024, there were no outstanding borrowings under these facilities and the aggregate amount of standby letters of credit outstanding was $50.6 million. As of June 30, 2024, we had no bank overdrafts related to our disbursement bank accounts.

We periodically use certain interest rate derivative contracts to hedge interest rate exposures on our variable rate debt. We also enter into foreign currency derivative contracts with financial institutions to reduce the risk that cash flows and earnings could adversely be affected by foreign currency exchange rate fluctuations. Our hedging program is not designated for trading or speculative purposes.

We recognize derivative instruments as either assets or liabilities on the accompanying consolidated balance sheets at fair value. We record changes in the fair value (i.e., gains or losses) of the derivatives that have been designated as cash flow hedges in our consolidated balance sheets as accumulated other comprehensive income, and in our consolidated statements of income for those derivatives designated as fair value hedges. Our derivative contracts are categorized within Level 2 of the fair value hierarchy.

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In the fourth quarter of fiscal 2022, we entered into a forward contract to acquire GBP 714.0 million at a rate of 1.0852 for a total of USD 774.8 million that was integrated with our plan to acquire RPS. This contract matured on December 30, 2022. On December 28, 2022, we entered into an extension of the integrated forward contract to acquire GBP 714.0 million at a rate of 1.086 for a total of USD 775.4 million, extending the maturity date to January 23, 2023, the closing date of the RPS acquisition. Although an effective economic hedge of our foreign exchange risk related to this transaction, the forward contract did not qualify for hedge accounting. As a result, the forward contract was marked-to-market with changes in fair value recognized in earnings each period. The intrinsic value of the forward contract was immaterial at inception as the GBP/USD spot and forward exchange rates were essentially the same. The fair value of the forward contract at October 2, 2022 was $19.9 million, and an unrealized gain of the same amount was recognized in our fourth quarter of fiscal 2022 results. On January 23, 2023, the forward contract was settled at the fair value of $109.3 million. We recognized additional gains of $68.0 million and $21.4 million in the first and second quarters of fiscal 2023, respectively. All gains related to this transaction were reported in “Other non-operating income" on our consolidated income statements for the respective periods.

In fiscal 2018, we entered into five interest rate swap agreements that we designated as cash flow hedges to fix the interest rate on the borrowings under our term loan facility. The five swaps expired on July 31, 2023. The related loss of $1.0 million and $2.0 million were recognized and reported on our consolidated statement of comprehensive income for the three and nine months ended July 2, 2023. There were no derivative instruments that were not designated as hedging instruments for the first nine months of fiscal 2024 and 2023.

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The accumulated balances and activities for the three and nine months ended June 30, 2024 and July 2, 2023 related to reclassifications out of accumulated other comprehensive income are summarized as follows (in thousands):

			Three Months Ended
			Foreign Currency Translation Adjustments						Gain (Loss) on Derivative Instruments						Net Pension Adjustments						Accumulated Other Comprehensive Income (Loss)
Balance at April 2, 2023			$	(185,602)					$	1,427					$	2,794					$	(181,381)
Other comprehensive income (loss) before reclassifications			44,499						(2,137)						—						42,362
Amounts reclassified from accumulated other comprehensive loss:
Interest rate contracts, net of tax (1)			—						1,093						—						1,093
Net current-period other comprehensive income (loss)			44,499						(1,044)						—						43,455
Balance at July 2, 2023			$	(141,103)					$	383					$	2,794					$	(137,926)
Balance at March 31, 2024			$	(159,171)					$	—					$	2,625					$	(156,546)
Other comprehensive income before reclassifications			1,854						—						3						1,857
Net current-period other comprehensive income			1,854						—						3						1,857
Balance at June 30, 2024			$	(157,317)					$	—					$	2,628					$	(154,689)
			Nine Months Ended
			Foreign Currency Translation Adjustments						Gain (Loss) on Derivative Instruments						Net Pension Adjustments						Accumulated Other Comprehensive Income (Loss)
Balance at October 2, 2022			$	(210,556)					$	2,412					—						$	(208,144)
Other comprehensive income (loss) before reclassifications			69,453						(4,439)						2,794						67,808
Amounts reclassified from accumulated other comprehensive loss:
Interest rate contracts, net of tax (1)			—						2,410						—						2,410
Net current-period other comprehensive income (loss)			69,453						(2,029)						2,794						70,218
Balance at July 2, 2023			$	(141,103)					$	383					$	2,794					$	(137,926)
Balance at October 1, 2023			$	(197,933)					$	—					$	2,638					$	(195,295)
Other comprehensive income (loss) before reclassifications			40,616						—						(10)						40,606
Net current-period other comprehensive income (loss)			40,616						—						(10)						40,606
Balance at June 30, 2024			$	(157,317)					$	—					$	2,628					$	(154,689)

(1)    This accumulated other comprehensive component is reclassified to “Interest expense” in our consolidated statements of income. See Note 16 “Derivative Financial Instruments”, for more information.

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We are subject to certain claims and lawsuits typically filed against the consulting and engineering profession, alleging primarily professional errors or omissions. We carry professional liability insurance, subject to certain deductibles and policy limits, against such claims. However, in some actions, parties are seeking damages that exceed our insurance coverage or for which we are not insured. While management does not believe that the resolution of these claims will have a material adverse effect, individually or in aggregate, on our financial position, results of operations or cash flows, management acknowledges the uncertainty surrounding the ultimate resolution of these matters.

On July 15, 2019, following an initial January 14, 2019 filing, the Civil Division of the United States Attorney's Office filed an amended complaint in intervention in three qui tam actions filed against our subsidiary, Tetra Tech EC, Inc. ("TtEC"), in the U.S. District Court for the Northern District of California. The complaint alleges False Claims Act violations and breach of contract related to TtEC's contracts to perform environmental remediation services at the former Hunters Point Naval Shipyard in San Francisco, California. TtEC disputes the claims and will defend this matter vigorously. We are currently unable to determine the probability of the outcome of this matter or the range of reasonably possible loss, if any.

We often provide services to unconsolidated joint ventures. The table below presents revenue and reimbursable costs related to services we provided to our unconsolidated joint ventures (in thousands):

			Three Months Ended												Nine Months Ended
			June 30, 2024						July 2, 2023						June 30, 2024						July 2, 2023
Revenue			$	16,753					$	22,373					$	50,157					$	65,249
Related reimbursable costs			15,287						20,848						46,025						61,475

Our consolidated balance sheets also included the following amounts related to these services (in thousands):

			Balance at
			June 30, 2024						October 1, 2023
Accounts receivable, net			$	14,305					$	19,944
Contract assets			1,997						2,723
Contract liabilities			(3,708)						(3,158)

On July 29, 2024, our Board of Directors declared a quarterly cash dividend of $0.29 per share payable on August 30, 2024 to stockholders of record as of the close of business on August 15, 2024.

On July 29, 2024, our Board of Directors also approved a five-for-one stock split of our common stock. The split will be effected through an amendment to our Restated Certificate of Incorporation, which will result in a proportionate increase in the number of shares of authorized common stock. The stock split is intended to make shares more accessible to a broader base of investors and enhance liquidity in the trading of Tetra Tech’s shares. Each record holder of common stock as of the close of market on September 5, 2024, will receive four additional shares of common stock. The stock split is expected to be effective after close of trading on September 6, 2024. Trading is expected to commence on a split-adjusted basis at market open on September 9, 2024. The following table reflects basic and diluted weighted average shares and net income per share on an unaudited pro forma basis giving effect to the stock split as if it had been effective for all periods presented:

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			Pro Forma (Unaudited)
			Three Months Ended												Nine Months Ended
			June 30, 2024						July 2, 2023						June 30, 2024						July 2, 2023
Net income attributable to Tetra Tech			$	85,810					$	60,235					$	237,228					$	219,771
Weighted-average common shares outstanding - basic			267,575						266,155						267,255						265,940
Effect of dilutive stock options and unvested restricted stock			2,165						2,110						2,075						2,135
Shares issuable assuming conversion of convertible notes			520						—						175						—
Weighted-average common shares outstanding - diluted			270,260						268,265						269,505						268,075
Earnings per share attributable to Tetra Tech:
Basic			$	0.32					$	0.23					$	0.89					$	0.83
Diluted			$	0.32					$	0.22					$	0.88					$	0.82

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v3.24.2.u1

Cover - shares	9 Months Ended
	Jun. 30, 2024	Jul. 22, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2024
Document Transition Report	false
Entity File Number	0-19655
Entity Registrant Name	TETRA TECH, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	95-4148514
Entity Address, Address Line One	3475 East Foothill Boulevard
Entity Address, City or Town	Pasadena
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	91107
City Area Code	626
Local Phone Number	351-4664
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	TTEK
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		53,532,413
Entity Central Index Key	0000831641
Amendment Flag	false
Current Fiscal Year End Date	--09-29
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3

v3.24.2.u1

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2024	Oct. 01, 2023
Current assets:
Cash and cash equivalents	$ 212,321	$ 168,831
Accounts receivable, net	1,053,758	974,535
Contract assets	118,556	113,939
Prepaid expenses and other current assets	121,846	98,719
Total current assets	1,506,481	1,356,024
Property and equipment, net	70,694	74,832
Right-of-use assets, operating leases	167,317	175,932
Goodwill	1,992,110	1,880,244
Intangible assets, net	164,459	173,936
Deferred tax assets	89,510	89,002
Other non-current assets	94,334	70,507
Total assets	4,084,905	3,820,477
Current liabilities:
Accounts payable	198,341	173,271
Accrued compensation	317,457	302,755
Contract liabilities	372,283	335,044
Short-term lease liabilities, operating leases	65,932	65,005
Current contingent earn-out liabilities	47,407	51,108
Other current liabilities	244,842	280,959
Total current liabilities	1,246,262	1,208,142
Deferred tax liabilities	17,254	14,256
Long-term debt	861,830	879,529
Long-term lease liabilities, operating leases	128,892	144,685
Non-current contingent earn-out liabilities	22,876	22,314
Other non-current liabilities	141,588	148,045
Commitments and contingencies (Note 18)
Equity:
Preferred stock - authorized, 2,000 shares of $0.01 par value; no shares issued and outstanding at June 30, 2024 and October 1, 2023	0	0
Common stock - authorized, 150,000 shares of $0.01 par value; issued and outstanding, 53,532 and 53,248 shares at June 30, 2024 and October 1, 2023, respectively	535	532
Additional paid-in capital	28,171	0
Accumulated other comprehensive loss	(154,689)	(195,295)
Retained earnings	1,792,121	1,598,196
Tetra Tech stockholders’ equity	1,666,138	1,403,433
Noncontrolling interests	65	73
Total stockholders' equity	1,666,203	1,403,506
Total liabilities and stockholders' equity	$ 4,084,905	$ 3,820,477

v3.24.2.u1

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2024	Oct. 01, 2023
Statement of Financial Position [Abstract]
Preferred stock, authorized shares (in shares)	2,000,000	2,000,000
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, authorized shares (in shares)	150,000,000	150,000,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares issued (in shares)	53,532,000	53,248,000
Common stock, shares outstanding (in shares)	53,532,000	53,248,000

v3.24.2.u1

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023
Revenue	$ 1,344,323	$ 1,208,947	$ 3,824,205	$ 3,261,938
Gross profit	223,172	188,846	621,165	512,937
Selling, general and administrative expenses	(94,042)	(89,064)	(263,293)	(227,912)
Acquisition and integration expenses	0	(2,107)	0	(25,812)
Contingent consideration – fair value adjustments	(500)	0	(477)	(8,477)
Income from operations	128,630	97,675	357,395	250,736
Interest expense, net	(9,912)	(14,869)	(29,374)	(33,563)
Other non-operating income	0	0	0	89,402
Income before income tax expense	118,718	82,806	328,021	306,575
Income tax expense	(32,894)	(22,568)	(90,758)	(86,781)
Net income	85,824	60,238	237,263	219,794
Net income attributable to noncontrolling interests	(14)	(3)	(35)	(23)
Net income attributable to Tetra Tech, basic	85,810	60,235	237,228	219,771
Net income attributable to Tetra Tech, diluted	$ 85,810	$ 60,235	$ 237,228	$ 219,771
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 1.60	$ 1.13	$ 4.44	$ 4.13
Diluted (in dollars per share)	$ 1.59	$ 1.12	$ 4.40	$ 4.10
Weighted-average common shares outstanding:
Basic (in shares)	53,515	53,231	53,451	53,188
Diluted (in shares)	54,052	53,653	53,901	53,615
Subcontractor costs
Cost of revenue	$ (234,742)	$ (221,387)	$ (646,828)	$ (568,252)
Other costs of revenue
Cost of revenue	$ (886,409)	$ (798,714)	$ (2,556,212)	$ (2,180,749)

v3.24.2.u1

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023
Statement of Comprehensive Income [Abstract]
Net income	$ 85,824	$ 60,238	$ 237,263	$ 219,794
Other comprehensive income, net of tax
Foreign currency translation adjustment, net of tax	1,854	44,500	40,616	69,453
Loss on cash flow hedge valuations, net of tax	0	(1,044)	0	(2,029)
Net pension adjustments	3	0	(10)	2,794
Other comprehensive income, net of tax	1,857	43,456	40,606	70,218
Comprehensive income, net of tax	87,681	103,694	277,869	290,012
Less: Comprehensive income attributable to noncontrolling interests, net of tax	14	4	35	23
Comprehensive income attributable to Tetra Tech, net of tax	$ 87,667	$ 103,690	$ 277,834	$ 289,989

v3.24.2.u1

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023
Cash flows from operating activities:
Net income	$ 237,263	$ 219,794
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	56,718	43,221
Amortization of stock-based awards	23,713	21,640
Deferred income taxes	(9,736)	21,475
Fair value adjustments to foreign currency forward contract	0	(89,402)
Fair value adjustments to contingent consideration	477	8,477
Other non-cash items	3,769	(796)
Changes in operating assets and liabilities, net of effects of business acquisitions:
Accounts receivable and contract assets	(54,286)	(41,824)
Prepaid expenses and other assets	(18,437)	1,970
Accounts payable	18,991	(3,678)
Accrued compensation	(7,982)	5,263
Contract liabilities	33,011	56,189
Income taxes receivable/payable	(16,436)	10,645
Other liabilities	(13,955)	(6,921)
Net cash provided by operating activities	253,110	246,053
Cash flows from investing activities:
Payments for business acquisitions, net of cash acquired	(93,650)	(854,319)
Settlement of foreign currency forward contract	0	109,306
Capital expenditures	(11,324)	(17,322)
Proceeds from sale of assets	666	439
Net cash used in investing activities	(104,308)	(761,896)
Cash flows from financing activities:
Proceeds from borrowings	180,000	979,859
Repayments on long-term debt	(200,000)	(411,676)
Shares repurchased for tax withholdings on share-based awards	(12,906)	(16,785)
Payments of contingent earn-out liabilities	(29,112)	(15,078)
Stock options exercised	2,690	425
Dividends paid	(43,303)	(38,268)
Principal payments on finance leases	(4,827)	(4,082)
Net cash (used in) provided by financing activities	(107,458)	494,395
Effect of exchange rate changes on cash and cash equivalents	2,146	12,410
Net increase (decrease) in cash and cash equivalents	43,490	(9,038)
Cash and cash equivalents at beginning of period	168,831	185,094
Cash and cash equivalents at end of period	212,321	176,056
Cash paid during the period for:
Interest	26,867	34,839
Income taxes, net of refunds received of $4.0 million and $1.5 million	$ 115,933	$ 54,967

v3.24.2.u1

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023
Statement of Cash Flows [Abstract]
Income tax refunds	$ 4.0	$ 1.5

v3.24.2.u1

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Total Tetra Tech Equity	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Retained Earnings	Non-Controlling Interests
Beginning balance (in shares) at Oct. 02, 2022			52,981
Beginning balance at Oct. 02, 2022	$ 1,183,137	$ 1,183,087	$ 530	$ 0	$ (208,144)	$ 1,390,701	$ 50
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	219,794	219,771				219,771	23
Other comprehensive income	70,218	70,218			70,218
Cash dividends per common share	(38,268)	(38,268)				(38,268)
Stock-based compensation	21,640	21,640		21,640
Restricted & performance shares released (in shares)			149
Restricted & performance shares released	(16,785)	(16,785)	$ 1	(16,786)
Stock options exercised (in shares)			15
Stock options exercised	425	425		425
Shares issued for Employee Stock Purchase Plan (in shares)			98
Shares issued for Employee Stock Purchase Plan	12,628	12,628	$ 1	12,627
Ending balance (in shares) at Jul. 02, 2023			53,243
Ending balance at Jul. 02, 2023	1,452,789	1,452,716	$ 532	17,906	(137,926)	1,572,204	73
Beginning balance (in shares) at Apr. 02, 2023			53,228
Beginning balance at Apr. 02, 2023	1,355,668	1,355,599	$ 532	10,639	(181,381)	1,525,809	69
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	60,238	60,235				60,235	3
Other comprehensive income	43,456	43,455			43,455		1
Cash dividends per common share	(13,840)	(13,840)				(13,840)
Stock-based compensation	7,038	7,038		7,038
Restricted & performance shares released (in shares)			3
Restricted & performance shares released	(105)	(105)		(105)
Stock options exercised (in shares)			12
Stock options exercised	334	334		334
Ending balance (in shares) at Jul. 02, 2023			53,243
Ending balance at Jul. 02, 2023	1,452,789	1,452,716	$ 532	17,906	(137,926)	1,572,204	73
Beginning balance (in shares) at Oct. 01, 2023			53,248
Beginning balance at Oct. 01, 2023	1,403,506	1,403,433	$ 532	0	(195,295)	1,598,196	73
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	237,263	237,228				237,228	35
Other comprehensive income	40,606	40,606			40,606
Distributions paid to noncontrolling interests	(43)						(43)
Cash dividends per common share	(43,303)	(43,303)				(43,303)
Stock-based compensation	23,713	23,713		23,713
Restricted & performance shares released (in shares)			108
Restricted & performance shares released	(12,906)	(12,906)	$ 1	(12,907)
Stock options exercised (in shares)			72
Stock options exercised	2,690	2,690	$ 1	2,689
Shares issued for Employee Stock Purchase Plan (in shares)			104
Shares issued for Employee Stock Purchase Plan	14,677	14,677	$ 1	14,676
Ending balance (in shares) at Jun. 30, 2024			53,532
Ending balance at Jun. 30, 2024	1,666,203	1,666,138	$ 535	28,171	(154,689)	1,792,121	65
Beginning balance (in shares) at Mar. 31, 2024			53,497
Beginning balance at Mar. 31, 2024	1,584,850	1,584,794	$ 535	18,972	(156,546)	1,721,833	56
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	85,824	85,810				85,810	14
Other comprehensive income	1,857	1,857			1,857
Distributions paid to noncontrolling interests	(5)						(5)
Cash dividends per common share	(15,522)	(15,522)				(15,522)
Stock-based compensation	8,096	8,096		8,096
Restricted & performance shares released (in shares)			1
Restricted & performance shares released	(125)	(125)		(125)
Stock options exercised (in shares)			34
Stock options exercised	1,228	1,228		1,228
Ending balance (in shares) at Jun. 30, 2024			53,532
Ending balance at Jun. 30, 2024	$ 1,666,203	$ 1,666,138	$ 535	$ 28,171	$ (154,689)	$ 1,792,121	$ 65

v3.24.2.u1

Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares							3 Months Ended		9 Months Ended
	May 31, 2024	Feb. 27, 2024	Dec. 13, 2023	Jun. 06, 2023	Feb. 24, 2023	Dec. 09, 2022	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023
Statement of Stockholders' Equity [Abstract]
Dividend paid per share (in dollars per share)	$ 0.29	$ 0.26	$ 0.26	$ 0.26	$ 0.23	$ 0.23	$ 0.29	$ 0.26	$ 0.81	$ 0.72

v3.24.2.u1

Basis of Presentation	9 Months Ended
	Jun. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited consolidated financial statements and related notes of Tetra Tech, Inc. (“we,” “us,” “our” or "Tetra Tech") have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. They do not include all of the information and footnotes required by U.S. GAAP for complete financial statements and, therefore, should be read in conjunction with the audited consolidated financial statements and the notes contained in our Annual Report on Form 10-K for the fiscal year ended October 1, 2023. These financial statements reflect all normal recurring adjustments that are considered necessary for a fair statement of our financial position, results of operations and cash flows for the interim periods presented. The results of operations and cash flows for any interim period are not necessarily indicative of results for the full fiscal year or for future fiscal years. Certain prior year amounts have been reclassified to conform to the current year presentation in the accompanying notes.

v3.24.2.u1

Recent Accounting Pronouncements	9 Months Ended
	Jun. 30, 2024
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements In November 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update (“ASU”) No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which requires that an entity report segment information in accordance with Topic 280, Segment Reporting. The amendments in the ASU are intended to improve reportable segment disclosure requirements primarily through enhanced disclosures about significant segment expenses. The amendments in this ASU are effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024 (fiscal 2025 for us). Early adoption is permitted. We are currently evaluating the impact of this guidance on our consolidated financial statements; however, we do not plan to adopt Topic 280 before fiscal 2025. In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which requires that an entity, on an annual basis, disclose additional income tax information, primarily related to the rate reconciliation and income taxes paid. The amendments in the ASU are intended to enhance the transparency and decision usefulness of income tax disclosures. The amendments in this ASU are effective for annual periods beginning after December 15, 2024 (fiscal 2026 for us). Early adoption is permitted. We are currently evaluating the impact of this guidance on our consolidated financial statements; however, we do not plan to adopt Topic 740 before fiscal 2026.

v3.24.2.u1

Revenue and Contract Balances	9 Months Ended
	Jun. 30, 2024
Revenue from Contract with Customer [Abstract]
Revenue and Contract Balances	Revenue and Contract Balances We disaggregate revenue by client sector and contract type, as we believe it best depicts how the nature, timing and uncertainty of our revenue and cash flows are affected by economic factors. The following tables present our revenue disaggregated by client sector and contract type (in thousands):   Three Months Ended Nine Months Ended   June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023 Client Sector:     U.S. federal government (1) $ 432,242  $ 338,022  $ 1,221,320  $ 996,471  U.S. state and local government 146,401  151,462  444,877  452,447  U.S. commercial 241,838  225,907  665,675  633,401  International (2) 523,842  493,556  1,492,333  1,179,619  Total $ 1,344,323  $ 1,208,947  $ 3,824,205  $ 3,261,938  Contract Type: Fixed-price $ 548,452  $ 452,605  $ 1,478,915  $ 1,194,266  Time-and-materials 589,301  596,904  1,730,796  1,550,970  Cost-plus 206,570  159,438  614,494  516,702  Total $ 1,344,323  $ 1,208,947  $ 3,824,205  $ 3,261,938  (1)    Includes revenue generated under U.S. federal government contracts performed outside the United States. (2)    Includes revenue generated from non-U.S. clients, primarily in Canada, Australia, Europe and the United Kingdom. Other than the U.S. federal government, no single client accounted for more than 10% of our revenue for the three and nine months ended June 30, 2024 and July 2, 2023. Contract Assets and Contract Liabilities We invoice customers based on the contractual terms of each contract. However, the timing of revenue recognition may differ from the timing of invoice issuance. Contract assets represent revenue recognized in excess of the amounts for which we have the contractual right to bill our customers. Such amounts are recoverable from customers based upon various measures of performance, including achievement of certain milestones or completion of a contract. In addition, many of our time-and-materials arrangements are billed in arrears pursuant to contract terms that are standard within the industry, resulting in contract assets and/or unbilled receivables being recorded, as revenue is recognized in advance of billings. Contract retentions, included in contract assets, represent amounts withheld by clients until certain conditions are met or the project is completed, which may extend beyond one year. Contract liabilities consist of billings in excess of revenue recognized. Contract liabilities decrease as we recognize revenue from the satisfaction of the related performance obligation and increase as billings in advance of revenue recognition occur. Contract assets and liabilities are reported in a net position on a contract-by-contract basis at the end of each reporting period. There were no substantial non-current contract assets or liabilities for the periods presented. Net contract assets/liabilities consisted of the following (in thousands): Balance at June 30, 2024 October 1, 2023 Contract assets (1) $ 118,556  $ 113,939  Contract liabilities (372,283) (335,044) Net contract liabilities $ (253,727) $ (221,105) (1)    Includes $6.2 million and $6.8 million of contract retentions at June 30, 2024 and October 1, 2023, respectively. Both our contract assets and contract liabilities increased in the third quarter of fiscal 2024 compared to fiscal 2023 year-end, due to the timing of our milestone billing on fixed-price contracts which were different from the timing of revenue recognition on those contracts. For the first nine months of fiscal 2024 and 2023, we recognized revenue of approximately $214 million and $143 million, respectively, from the amounts included in the contract liability balances at the end of fiscal 2023 and 2022, respectively. Revenue is recognized by measuring progress over time under Accounting Standards Codification Topic 606, "Revenue from Contracts with Customers". We estimate and measure progress on our contracts over time whereby we compare our total costs incurred on each contract as a percentage of the total expected contract costs. Changes in those estimates could result in the recognition of cumulative catch-up adjustments to the contract’s inception-to-date revenue, costs and profit in the period in which such changes are made. As a result, for the third quarter and first nine months of fiscal 2024, we recognized net favorable revenue and operating income adjustments of $6.5 million and $16.4 million, respectively. For the first nine months of fiscal 2023, we recognized net favorable revenue and operating income adjustments of $4.0 million (substantially all in the first quarter). Changes in revenue and cost estimates could also result in a projected loss, determined at the contract level, which would be recorded immediately in earnings. At June 30, 2024 and October 1, 2023, our consolidated balance sheets included liabilities for anticipated losses of $15.0 million and $8.5 million, respectively. The estimated cost to complete these related contracts was approximately $95 million and $68 million at June 30, 2024 and October 1, 2023, respectively. Accounts Receivable, Net Net accounts receivable consisted of the following (in thousands): Balance at   June 30, 2024 October 1, 2023 Billed $ 685,184  $ 672,712  Unbilled 372,913  306,788  Total accounts receivable 1,058,097  979,500  Allowance for doubtful accounts (4,339) (4,965) Total accounts receivable, net $ 1,053,758  $ 974,535  Billed accounts receivable represent amounts billed to clients that have not been collected. Unbilled accounts receivable, which represent an unconditional right to payment subject only to the passage of time, include unbilled amounts typically resulting from revenue recognized but not yet billed pursuant to contract terms or billed after the period end date. Substantially all of our unbilled receivables at June 30, 2024 are expected to be billed and collected within 12 months. The allowance for doubtful accounts represents amounts that are expected to become uncollectible or unrealizable in the future. We determine an estimated allowance for uncollectible accounts based on management's consideration of trends in the actual and forecasted credit quality of our clients, including delinquency and payment history; type of client, such as a government agency or a commercial sector client; and general economic and industry conditions, which may affect our clients' ability to pay. Other than the U.S. federal government, no single client accounted for more than 10% of our accounts receivable at June 30, 2024 and October 1, 2023. Remaining Unsatisfied Performance Obligation (“RUPO”) Our RUPO represents a measure of the total dollar value of work to be performed on contracts awarded and in progress. We had $5.2 billion of RUPO at June 30, 2024. Our RUPO increases with awards from new contracts or additions on existing contracts, and decreases as work is performed and revenue is recognized on existing contracts. Our RUPO may also decrease when projects are canceled or modified in scope. We include a contract within our RUPO when the contract is awarded and an agreement on contract terms has been reached. We expect to satisfy our RUPO at June 30, 2024 over the following periods (in thousands): Amount Within 12 months $ 3,508,571  Beyond 1,683,295  Total $ 5,191,866  Although RUPO reflects business that is considered to be firm, cancellations, deferrals or scope adjustments may occur. Our RUPO is adjusted to reflect any known project cancellations, revisions to project scope and cost, foreign currency exchange fluctuations and project deferrals, as appropriate. Our operations and maintenance contracts can generally be terminated by the clients without a substantive financial penalty; therefore, the remaining performance obligations on such contracts are limited to the notice period required for the termination (usually 30, 60, or 90 days).

v3.24.2.u1

Acquisitions	9 Months Ended
	Jun. 30, 2024
Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]
Acquisitions	Acquisitions In the second quarter of fiscal 2024, we acquired LS Technologies ("LST"), an innovative U.S. federal enterprise technology services and management consulting firm based in Fairfax, Virginia. LST provides high-end consulting and engineering services including advanced data analytics, cybersecurity and digital transformation solutions to U.S. government clients. In the third quarter of fiscal 2024, we also acquired Convergence Controls & Engineering ("CCE"), an industry leader in process automation and systems integration solutions. CCE’s expertise includes customized digital controls and software solutions, advanced data analytics, cloud data integration, and cybersecurity applications. Both LST and CCE are included in our Government Services Group ("GSG") segment. The aggregate fair value of the purchase price of these two acquisitions was $120 million. This amount consisted of $93 million in initial cash payments, $4 million of cash holdback related to a tax reserve, and $23 million for the estimated fair value of contingent earn-out obligations, with a maximum of $60 million, based upon the achievement of specified operating income targets in each of the three years following the acquisition dates. The $120 million purchase price was allocated $12 million to net tangible assets, $23 million to identifiable intangible assets, and $85 million to goodwill. The purchase price allocation is preliminary and subject to adjustment as the estimates, assumptions, valuations and other analyses have not yet been finalized in order to make a definitive allocation. These acquisitions were not considered material, individually or in aggregate, to our consolidated financial statements. As a result, no pro forma information has been provided. On September 23, 2022, we made an all cash offer to acquire all the outstanding shares of RPS Group plc ("RPS"), a publicly traded company on the London Stock Exchange for 222 pence per share, through a scheme of arrangement, which was unanimously recommended by RPS' Board of Directors. On November 3, 2022, RPS' shareholders approved the scheme of arrangement. On January 19, 2023, the court-sanctioned scheme of arrangement to purchase RPS was approved, and we completed the acquisition on January 23, 2023. RPS employs approximately 5,000 associates in the United Kingdom, Europe, Asia Pacific and North America, delivering high-end solutions, especially in energy transformation, water and program management for government and commercial clients. Substantially all of RPS is included in our Commercial/International Services Group ("CIG") segment. The total purchase price for RPS was approximately £633 million ($784 million). In the third quarter and first nine months of fiscal 2023, we incurred $2.1 million and $25.8 million, respectively, of acquisition and integration costs primarily for professional fees, substantially all of which were paid as of the end of the third quarter of fiscal 2023. On January 23, 2023, we also settled a foreign exchange forward contract that was integral to our plan to finance the RPS acquisition. The cash gain of $109.3 million did not qualify for hedge accounting. As a result, the gain was recognized as non-operating income over the life of the contract and not included in the purchase price allocation below. However, the cash proceeds of $109.3 million economically reduced the purchase price for the shares of RPS to approximately $675 million. This forward contract is explained further in Note 16, "Derivative Financial Instruments". The table below represents the purchase price allocation for RPS based on estimates, assumptions, valuations and other analyses as of January 23, 2023. The all cash purchase consideration, excluding the aforementioned forward contract gain, was allocated to the tangible and intangible assets, and liabilities of RPS based on their estimated fair values, with any excess purchase consideration allocated to goodwill as follows (in thousands): Amount Cash and cash equivalents $ 32,093  Accounts receivable and contract assets 202,303  Prepaid expenses and other current assets 45,999  Income taxes receivables 1,999  Property and equipment 38,435  Right-of-use assets, operating leases 40,179  Intangible assets 174,094  Deferred income taxes 35,084  Other long-term assets 1,061  Total assets acquired 571,247  Accounts payable $ (44,376) Accrued compensation (19,073) Contract liabilities (46,287) Income tax payable (7,083) Short-term lease liabilities, operating leases (13,477) Other current liabilities (135,474) Current portion of long-term debt (91,973) Long-term lease liabilities, operating leases (26,702) Other long-term liabilities (13,742) Deferred tax liabilities (41,613) Total liabilities assumed (439,800) Fair value of net assets acquired 131,447  Goodwill 652,762  Total purchase consideration $ 784,209  The following table summarizes the estimated fair values that were assigned to intangible assets at the acquisition date: Fair Value Weighted-Average Estimated Useful Life (in thousands) (in years) Backlog $ 27,880  1.6 Trade names 27,260  3.0 Client relations 118,954  11.1 Total intangible assets acquired $ 174,094  8.3 Estimated fair value measurements for the intangible assets related to the RPS acquisition were made using Level 3 inputs including discounted cash flow techniques. Fair value was estimated using a multi-period excess earnings method for backlog and client relations and a relief from royalty method for trade names. The significant assumptions used in estimating fair value of backlog and client relations include (i) the estimated life the asset will contribute to cash flows, such as remaining contractual terms, (ii) revenue growth rates and EBITDA margins, (iii) attrition rate of customers, and (iv) the estimated discount rates that reflect the level of risk associated with receiving future cash flows. The significant assumptions used in estimating fair value of trade names include the royalty rates and discount rates. Supplemental Pro Forma Information (Unaudited) Following are the supplemental consolidated financial results of Tetra Tech and RPS for the third quarter and first nine months of fiscal 2023 on an unaudited pro forma basis, as if the RPS acquisition had been consummated at the beginning of fiscal 2023 (in thousands): Three Months Ended Nine Months Ended July 2, 2023 July 2, 2023 Revenue $ 1,208,947  $ 3,519,792  Net income including noncontrolling interests 61,770  104,564  In fiscal 2023, we also acquired Amyx, Inc. (“Amyx”), an enterprise technology services, cybersecurity and management consulting firm based in Reston, Virginia. With over 500 employees, Amyx provides application modernization, cybersecurity, systems engineering, financial management and program management support on over 30 Federal Government programs. Amyx is included in our GSG segment. The total fair value of the purchase price of Amyx was $120.9 million, consisted of a $100.0 million payable in a promissory note issued to the sellers (paid subsequent to closing), $8.7 million of payables related to estimated post-closing adjustments, and $12.2 million for the estimated fair value of contingent earn-out obligations, with a maximum of $25.0 million, based upon the achievement of specified operating income targets in each of the three years following the acquisition date. Amyx was not considered material to our consolidated financial statements. As a result, no pro forma information has been provided. The fiscal 2024 goodwill addition from LST and CCE are deductible for tax purposes, while the majority of the goodwill from the fiscal 2023 acquisitions is not deductible for tax purposes. The results of fiscal 2024 and 2023 acquisitions were included in our consolidated financial statements beginning on their respective closing dates. Our fiscal 2024 goodwill additions from the LST and CCE acquisitions reflect the extensive technical knowledge of the acquired workforces, the anticipated synergies in data analytics, cybersecurity and digital transformation services, and collective reputations of these acquisitions in providing mission critical solutions to both commercial and government customers. The goodwill additions from fiscal 2023 business combinations are primarily attributable to the significant technical expertise residing in embedded workforces that are sought out by clients, synergies expected to arise after the acquisitions in the areas of enterprise technology services, data management, energy transformation, water, program management, and data analytics and the long-standing reputations of RPS and Amyx. These acquisitions further expand and complement our market-leading positions in water and environment; enhanced by a combined suite of differentiated data analytics and digital technologies, and expansion into existing and new geographies. Intangible assets with finite lives arise from business acquisitions and are amortized based on the period over which the contractual or economic benefit of the intangible assets are expected to be realized on a straight-line basis over the useful lives of the underlying assets, ranging from one to 12 years. These consist of client relations, backlog and trade names. For detailed information regarding our intangible assets, see Note 5, “Goodwill and Intangible Assets”. Most of our acquisition agreements include contingent earn-out agreements, which are generally based on the achievement of future operating income thresholds. The contingent earn-out arrangements are based on our valuations of the acquired companies and reduce the risk of overpaying for acquisitions if the projected financial results are not achieved. The fair values of any earn-out arrangements are included as part of the purchase price of the acquired companies on their respective acquisition dates. For each transaction, we estimate the fair value of contingent earn-out payments as part of the initial purchase price and record the estimated fair value of contingent consideration as a liability in “Current contingent earn-out liabilities” and “Non-current contingent earn-out liabilities” on the consolidated balance sheets. We consider several factors when determining that contingent earn-out liabilities are part of the purchase price, including the following: (1) the valuation of our acquisitions is not supported solely by the initial consideration paid, and the contingent earn-out formula is a critical and material component of the valuation approach to determining the purchase price; and (2) the former owners of acquired companies that remain as key employees receive compensation other than contingent earn-out payments at a reasonable level compared with the compensation of our other key employees. The contingent earn-out payments are not affected by employment termination. We measure our contingent earn-out liabilities at fair value on a recurring basis using significant unobservable inputs classified within Level 3 of the fair value hierarchy. We use a probability-weighted discounted income approach as a valuation technique to convert future estimated cash flows to a single present value amount. The significant unobservable inputs used in the fair value measurements are operating income projections over the earn-out period (generally three to five years), and the probability outcome percentages we assign to each scenario. Significant increases or decreases to either of these inputs in isolation would result in a significantly higher or lower liability, with a higher liability capped by the contractual maximum of the contingent earn-out obligation. Ultimately, the liability will be equivalent to the amount paid, and the difference between the fair value estimate and amount paid will be recorded in earnings. The amount paid that is less than or equal to the contingent earn-out liability on the acquisition date is reflected as cash used in financing activities in our consolidated statements of cash flows. Any amount paid in excess of the contingent earn-out liability on the acquisition date is reflected as cash used in operating activities in our consolidated statements of cash flows. We review and reassess the estimated fair value of contingent consideration on a quarterly basis, and the updated fair value could differ materially from the initial estimates. Changes in the estimated fair value of our contingent earn-out liabilities related to the time component of the present value calculation are reported in interest expense. Adjustments to the estimated fair value related to changes in all other unobservable inputs are reported in operating income. In the first nine months of fiscal 2024, we evaluated our estimates for contingent consideration liabilities for the remaining earn-out periods for each individual acquisition, which included a review of their financial results to-date, the status of ongoing projects in their RUPO, and the inventory of prospective new contract awards. During the third quarter and first nine months of fiscal 2024, we recorded immaterial adjustments, individually and in aggregate, to our contingent earn-out liabilities and included the corresponding amount in our operating income. During the first nine months of fiscal 2023, we recorded adjustments to our contingent earn-out liabilities and reported a related net loss in operating income of $8.5 million (largely in the second quarter). The net loss primarily resulted from increased valuation of the contingent consideration liabilities for our prior acquisitions of Segue Technologies, Inc., Hoare Lea, LLP and The Integration Group of Americas, Inc., reflecting financial performance that exceeded our previous expectations. The following table summarizes the changes in the fair value of estimated contingent consideration (in thousands): Three Months Ended Nine Months Ended   June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023 Beginning balance $ 74,579  $ 88,082  $ 73,422  $ 65,566  Estimated earn-out liabilities for acquisitions 1,138  —  23,038  12,248  Payments of contingent consideration (7,000) (13,078) (29,112) (15,078) Adjustments to fair value recorded in earnings 500  —  477  8,477  Interest accretion expense 1,038  707  1,953  1,919  Effect of foreign currency exchange rate changes 28  888  505  3,467  Ending balance $ 70,283  $ 76,599  $ 70,283  $ 76,599  Maximum potential payout at end of period $ 128,573  $ 120,320  $ 128,573  $ 120,320

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Goodwill and Intangible Assets	9 Months Ended
	Jun. 30, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets The following table summarizes the changes in the carrying value of goodwill by reportable segment (in thousands):   GSG CIG Total Balance at October 1, 2023 $ 659,942  $ 1,220,302  $ 1,880,244  Acquisition activity 84,865  —  84,865  Translation and other adjustments 2,282  24,719  27,001  Balance at June 30, 2024 $ 747,089  $ 1,245,021  $ 1,992,110  The goodwill addition in GSG resulted from the purchase price allocations for our fiscal 2024 acquisitions which are preliminary and subject to adjustment based upon the final determinations of the net assets acquired and information to perform the final valuation. Goodwill adjustments primarily related to the foreign currency translation adjustments which resulted from our foreign subsidiaries with functional currencies that are different than our reporting currency. These goodwill amounts are presented net of reductions from historical impairment adjustments. The gross amounts for GSG were $764.8 million and $677.6 million at June 30, 2024 and October 1, 2023, respectively, excluding accumulated impairment of $17.7 million at each date. The gross amounts of goodwill for CIG were $1,366.5 million and $1,341.8 million at June 30, 2024 and October 1, 2023, respectively, excluding accumulated impairment of $121.5 million at each date. We perform our annual goodwill impairment review at the beginning of our fiscal fourth quarter. Our most recent annual review at July 3, 2023 (i.e. the first day of our fourth quarter in fiscal 2023) indicated that we had no impairment of goodwill, and all of our reporting units had estimated fair values that were in excess of their carrying values, including goodwill. At July 3, 2023, we had no reporting units that had estimated fair values that exceeded their carrying values by less than 45%. We also regularly evaluate whether events and circumstances have occurred that may indicate a potential change in the recoverability of goodwill. We perform interim goodwill impairment reviews between our annual reviews if certain events and circumstances have occurred, such as a deterioration in general economic conditions; an increase in the competitive environment; a change in management, key personnel, strategy or customers; negative or declining cash flows; or a decline in actual or planned revenue or earnings compared with actual and projected results of relevant prior periods. Although we believe that our estimates of fair value for these reporting units are reasonable, if financial performance for these reporting units falls significantly below our expectations or market prices for similar business decline, the goodwill for these reporting units could become impaired. The following table presents the gross amount and accumulated amortization of our acquired identifiable intangible assets with finite useful lives included in “Intangible assets, net” on the consolidated balance sheets ($ in thousands): Period Ended   June 30, 2024 October 1, 2023   Weighted- Average Remaining Life (in Years) Gross Amount Accumulated Amortization Net Amount Gross Amount Accumulated Amortization Net Amount   Client relations 8.4 $ 190,329  $ (50,980) $ 139,349  $ 169,217  $ (36,072) $ 133,145  Backlog 0.6 72,579  (65,050) 7,529  63,825  (47,802) 16,023  Trade names 1.7 38,773  (21,192) 17,581  37,411  (12,643) 24,768  Total   $ 301,681  $ (137,222) $ 164,459  $ 270,453  $ (96,517) $ 173,936  Amortization expense for the third quarter and first nine months of fiscal 2024 was $13.8 million and $38.4 million, compared to $14.1 million and $29.6 million, respectively, for the prior-year periods. Estimated amortization expense for the remainder of fiscal 2024 and succeeding years is as follows (in thousands):   Amount   2024 (remaining) $ 11,322  2025 34,712  2026 23,334  2027 16,830  2028 16,320  Beyond 61,941  Total $ 164,459

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Property and Equipment	9 Months Ended
	Jun. 30, 2024
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and Equipment Property and equipment consisted of the following (in thousands): Balance at   June 30, 2024 October 1, 2023   Equipment, furniture and fixtures $ 130,748  $ 132,744  Leasehold improvements 46,042  44,733  Total property and equipment 176,790  177,477  Accumulated depreciation (106,096) (102,645) Property and equipment, net $ 70,694  $ 74,832  For the third quarter and first nine months of fiscal 2024, our depreciation expense related to property and equipment was $5.7 million and $18.3 million, respectively, compared to $5.6 million and $13.7 million for third quarter and first nine months of fiscal 2023, respectively.

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Stock Repurchase and Dividends	9 Months Ended
	Jun. 30, 2024
Stock Repurchase And Dividends [Abstract]
Stock Repurchase and Dividends	Stock Repurchase and Dividends On October 5, 2021, our Board of Directors authorized a new stock repurchase program under which we could repurchase up to $400 million of our common stock. We did not repurchase any shares of our common stock in the first nine months of fiscal 2024 and 2023. At June 30, 2024, we had a remaining balance of $347.8 million under our stock repurchase program. The following table presents dividends declared and paid in the first nine months of fiscal 2024 and 2023: Declare Date Dividend Paid Per Share Record Date Payment Date Dividend Paid (in thousands) November 13, 2023 $ 0.26  November 30, 2023 December 13, 2023 $ 13,873  January 29, 2024 0.26  February 14, 2024 February 27, 2024 13,908  April 29, 2024 0.29  May 20, 2024 May 31, 2024 15,522  Total dividend paid as of June 30, 2024 $ 43,303  November 7, 2022 $ 0.23  November 21, 2022 December 9, 2022 $ 12,186  January 30, 2023 0.23  February 13, 2023 February 24, 2023 12,242  May 8, 2023 0.26  May 24, 2023 June 6, 2023 13,840  Total dividend paid as of July 2, 2023 $ 38,268

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Leases	9 Months Ended
	Jun. 30, 2024
Leases [Abstract]
Leases	Leases Our operating leases are primarily for corporate and project office spaces. To a much lesser extent, we have operating leases for vehicles and equipment. Our operating leases have remaining lease terms of one month to ten years, some of which may include options to extend the leases for up to five years. We determine if an arrangement is a lease at inception. Operating leases are included in "Right-of-use assets, operating leases", "Short-term lease liabilities, operating leases" and "Long-term lease liabilities, operating leases" in the consolidated balance sheets. Our finance leases are primarily for certain IT equipment and are immaterial. Right-of-use ("ROU") assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. As most of our leases do not provide an implicit rate, incremental borrowing rates are used based on the information available at commencement date in determining the present value of lease payments. The operating lease ROU asset at the commencement date also includes any lease payments made to the lessor at or before the commencement date and initial direct costs less lease incentives received. Lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise that option. Lease expense for operating lease payments is recognized on a straight-line basis over the lease term. The components of lease costs are as follows (in thousands): Three Months Ended Nine Months Ended June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023 Operating lease cost $ 24,562  $ 24,775  $ 73,580  $ 70,155  Sublease income (184) (46) (347) (125) Total lease cost $ 24,378  $ 24,729  $ 73,233  $ 70,030  Supplemental cash flow information related to leases is as follows (in thousands): Nine Months Ended June 30, 2024 July 2, 2023 Operating cash flows for operating leases $ 56,379  $ 57,871  Right-of-use assets obtained in exchange for new operating lease liabilities 38,160  72,294  Supplemental balance sheet and other information related to leases are as follows (in thousands): Balance at June 30, 2024 October 1, 2023 Operating leases: Right-of-use assets $ 167,317  $ 175,932  Lease liabilities: Current 65,932  65,005  Non-current 128,892  144,685  Total operating lease liabilities $ 194,824  $ 209,690  Weighted-average remaining lease term: Operating leases 4 years 5 years Weighted-average discount rate: Operating leases 3.4  % 3.0  % At June 30, 2024, we had $13.9 million of operating leases that have not yet commenced. A maturity analysis of the future undiscounted cash flows associated with our lease liabilities at June 30, 2024 is as follows (in thousands): Operating Leases 2024 (remaining) $ 20,124  2025 65,068  2026 44,638  2027 31,231  2028 20,176  Beyond 28,412  Total lease payments 209,649   Less: imputed interest (14,825) Total present value of lease liabilities $ 194,824

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Employee Benefits	9 Months Ended
	Jun. 30, 2024
Retirement Benefits [Abstract]
Employee Benefits	Employee Benefits In fiscal 2020, the Canadian federal government implemented the Canadian Emergency Wage Subsidy ("CEWS") program in response to the negative impact of the coronavirus disease 2019 pandemic on businesses operating in Canada. Some of our Canadian legal entities qualified for and applied for these CEWS cash benefits to partially offset the impacts of revenue reductions and on-going staffing costs. The $21 million total received was initially recorded in "Other long-term liabilities" until all potential amendments to the qualification criteria, including some that were proposed with retroactive application, were finalized in fiscal 2022. In the first nine months of fiscal 2024 (all in the first quarter of fiscal 2024), we distributed approximately $10 million to our Canadian employees. The remaining $11 million, which we expect to distribute within one year, is reported in "Accrued compensation". We do not expect there will be any related impact on our operating income, and we have no outstanding applications for further government assistance.

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Stockholders' Equity and Stock Compensation Plans	9 Months Ended
	Jun. 30, 2024
Stockholders' Equity Note [Abstract]
Stockholders' Equity and Stock Compensation Plans	Stockholders’ Equity and Stock Compensation Plans We recognize the fair value of our stock-based awards as compensation expense on a straight-line basis over the requisite service period in which the award vests. Stock-based compensation expense for the three and nine months ended June 30, 2024 was $8.1 million and $23.7 million, compared to $7.0 million and $21.6 million for the same periods last year. Most of these amounts were included in selling, general and administrative expenses on our consolidated statements of income. In the first nine months of fiscal 2024, we awarded 55,836 performance share units (“PSUs”) to our non-employee directors and executive officers at an estimated fair value of $203.53 per share on the award date. All PSUs are performance-based and vest, if at all, after the conclusion of the three-year performance period. The number of PSUs that ultimately vest is based 50% on the growth in our diluted earnings per share and 50% on our relative total shareholder return over the vesting period. Additionally, we awarded 141,880 restricted stock units (“RSUs”) to our non-employee directors, executive officers and employees at a fair value of $164.78 per share on the award date. All executive officer and employee RSUs have time-based vesting over a four-year period, and the non-employee director RSUs vest after one year.

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Earnings per Share ("EPS")	9 Months Ended
	Jun. 30, 2024
Earnings Per Share [Abstract]
Earnings per Share ("EPS")	Earnings per Share (“EPS”) Basic EPS is computed by dividing net income available to common stockholders by the weighted-average number of common shares outstanding, less unvested restricted stock for the period. Diluted EPS is computed by dividing net income by the weighted-average number of common shares outstanding and dilutive potential common shares for the period. Potential common shares include the weighted-average dilutive effects of stock-based awards and shares underlying our Convertible Senior Notes (the "Convertible Notes"). For the third quarter and first nine months of fiscal 2024, our Convertible Notes, described in Note 15, "Long-Term Debt", had a dilution impact on the dilutive potential common shares, which was calculated using the if-converted method. The dilution impact was due to the price of our common stock exceeding the conversion price. The related capped call transactions (the "Capped Call Transactions") were excluded from the calculation of dilutive potential common shares as their effect is anti-dilutive. For the third quarters and first nine months of fiscal 2024 and 2023, no options were excluded from the calculation of dilutive potential common shares. The following table presents the number of weighted-average shares used to compute basic and diluted EPS (in thousands, except per share data):   Three Months Ended Nine Months Ended   June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023   Net income attributable to Tetra Tech $ 85,810  $ 60,235  $ 237,228  $ 219,771  Weighted-average common shares outstanding – basic 53,515  53,231  53,451  53,188  Effect of dilutive stock options and unvested restricted stock 433  422  415  427  Shares issuable assuming conversion of convertible notes 104  —  35  —  Weighted-average common shares outstanding – diluted 54,052  53,653  53,901  53,615  Earnings per share attributable to Tetra Tech:         Basic $ 1.60  $ 1.13  $ 4.44  $ 4.13  Diluted $ 1.59  $ 1.12  $ 4.40  $ 4.10

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Income Taxes	9 Months Ended
	Jun. 30, 2024
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The effective tax rates for the first nine months of fiscal 2024 and 2023 were 27.7% and 28.3%, respectively. Income tax expense was reduced by $2.9 million and $2.2 million of excess tax benefits on share-based payments in the first nine months of fiscal 2024 and 2023, respectively. In addition, income tax expense in the first nine months of fiscal 2024 included $4.3 million of expense for the settlement of various tax positions that were under audit for fiscal years 2018 through 2021. Furthermore, income tax expense in the first nine months of fiscal 2023 included non-operating income tax expenses of $7.2 million ($6.9 million in the second quarter) to recognize the tax liability for foreign earnings, primarily in the United Kingdom and Australia, that are no longer indefinitely reinvested and to increase the liability for an uncertain tax position. Excluding the impact of the excess tax benefits on share-based payments, the settlement amounts in the first nine months of fiscal 2024 and the additional $7.2 million in the first nine months of fiscal 2023, our effective tax rates in the first nine months of fiscal 2024 and 2023 were 27.2% and 26.7%, respectively. At June 30, 2024 and October 1, 2023, the liability for income taxes associated with uncertain tax positions was $64.0 million and $62.0 million, respectively. It is reasonably possible that the liabilities with respect to certain of our unrecognized tax positions may significantly decrease in the next 12 months. These changes would be the result of ongoing examinations. These liabilities represent our current estimates of the additional tax liabilities that we may be assessed when the related audits are concluded. If these audits are resolved in a manner more unfavorable than our current expectations, our tax liabilities could be materially higher than the amounts currently recorded resulting in additional tax expense.

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Reportable Segments	9 Months Ended
	Jun. 30, 2024
Segment Reporting [Abstract]
Reportable Segments	Reportable Segments We manage our operations under two reportable segments. Our GSG reportable segment primarily includes activities with U.S. government clients (federal, state and local) and all activities with development agencies worldwide. Our CIG reportable segment primarily includes activities with U.S. commercial clients and international clients other than development agencies. GSG provides high-end consulting and engineering services primarily to U.S. government clients (federal, state and local) and international development agencies worldwide. GSG supports U.S. government civilian and defense agencies with services in water, environment, sustainable infrastructure, information technology and disaster management. GSG also provides engineering design services for U.S. based federal and municipal clients, especially in water infrastructure, flood protection and solid waste. GSG also leads our support for development agencies worldwide, especially in the United States, United Kingdom and Australia. CIG primarily provides high-end consulting and engineering services to U.S. commercial clients, and international clients inclusive of the commercial and government sectors. CIG supports commercial clients worldwide in renewable energy, industrial, high performance buildings and aerospace markets. CIG also provides sustainable infrastructure and related environmental, engineering and project management services to commercial and local government clients across Canada, in Asia Pacific (primarily Australia and New Zealand), Europe, the United Kingdom and South America (primarily Brazil). Management evaluates the performance of these reportable segments based upon their respective segment operating income before the effect of amortization expense related to acquisitions, and other unallocated corporate expenses. We account for inter-segment revenues and transfers as if they were to third parties; that is, by applying a negotiated fee onto the costs of the services performed. All significant intercompany balances and transactions are eliminated in consolidation. In the third quarter and first nine months of fiscal 2023, our Corporate segment operating losses included $2.1 million and $25.8 million of acquisition and integration expenses, respectively, as described in Note 4, “Acquisitions”. The following tables summarize financial information regarding our reportable segments (in thousands):   Three Months Ended Nine Months Ended   June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023   Revenue         GSG $ 640,553  $ 531,050  $ 1,812,721  $ 1,565,371  CIG 723,617  691,386  2,063,879  1,741,300  Elimination of inter-segment revenue (19,847) (13,489) (52,395) (44,733) Total revenue $ 1,344,323  $ 1,208,947  $ 3,824,205  $ 3,261,938  Income from operations         GSG $ 71,518  $ 54,496  $ 198,652  $ 167,053  CIG 86,465  69,572  233,821  172,199  Corporate (1) (29,353) (26,393) (75,078) (88,516) Total income from operations $ 128,630  $ 97,675  $ 357,395  $ 250,736  (1)     Includes amortization of intangibles, acquisition and integration expenses, as well as other costs and other income not allocable to our reportable segments. Balance at   June 30, 2024 October 1, 2023   Total Assets     GSG $ 632,346  $ 543,066  CIG 1,066,241  994,470  Corporate (1) 2,386,318  2,282,941  Total assets $ 4,084,905  $ 3,820,477  (1)    Corporate assets consist of intercompany eliminations and assets not allocated to our reportable segments including goodwill, intangible assets, deferred income taxes and certain other assets.

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Fair Value Measurements	9 Months Ended
	Jun. 30, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements We classified our assets and liabilities that were carried at fair value in one of the following categories: •Level 1: Quoted market prices in active markets for identical assets or liabilities. •Level 2: Observable market-based inputs or unobservable inputs that are corroborated by market data. •Level 3: Unobservable inputs that are not corroborated by market data. Derivative Instruments. Our derivative instruments are categorized within Level 2 of the fair value hierarchy. For additional information about our derivative financial instruments (see Note 16, "Derivative Financial Instruments"). Contingent Consideration. We measure our contingent earn-out liabilities at fair value on a recurring basis using significant unobservable inputs classified within Level 3 of the fair value hierarchy. (see Note 4, "Acquisitions" for further information). Debt. The fair value of long-term debt under our Credit Facility was determined using the present value of future cash flows based on the borrowing rates currently available for debt with similar terms and maturities (Level 2 measurement, as described in “Critical Accounting Policies and Estimates” in our Annual Report on Form 10-K for the fiscal year ended October 1, 2023). The carrying value of our long-term debt under our Credit Facility approximated fair value at June 30, 2024 and October 1, 2023. At June 30, 2024, we had $300 million in outstanding borrowings under the Amended Credit Agreement, which was consisted of $300 million under the New Term Loan Facility and no borrowings under the Amended Revolving Credit Facility. The estimated fair value of our $575 million Convertible Notes was determined based on the trading price of the Convertible Notes as of the last trading day of our third quarter of fiscal 2024. We consider the fair value of the Convertible Notes to be a Level 2 measurement as they are not actively traded in markets. The carrying amounts and estimated fair values of the Convertible Notes were approximately $563 million and $674 million, respectively, at June 30, 2024, and $561 million and $566 million, respectively, at October 1, 2023.

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Long-Term Debt	9 Months Ended
	Jun. 30, 2024
Debt Disclosure [Abstract]
Long-Term Debt	Long-Term Debt Long-term debt consisted of the following (in thousands): Balance at   June 30, 2024 October 1, 2023   Credit facilities $ 300,000  $ 320,000  Convertible notes 575,000  575,000  Debt issuance costs and discount (13,170) (15,471) Long-term debt $ 861,830  $ 879,529  On August 22, 2023, we issued $575.0 million in Convertible Notes that bear interest at a rate of 2.25% per annum payable in arrears on February 15 and August 15 of each year, beginning on February 15, 2024, and mature on August 15, 2028, unless converted, redeemed or repurchased. Prior to May 15, 2028, the Convertible Notes will be convertible at the option of the holders only upon the occurrence of certain events and during certain periods. Thereafter, the Convertible Notes will be convertible at the option of the holders at any time until the close of business on the second scheduled trading day immediately preceding the maturity date. The initial conversion rate applicable to the Convertible Notes was 5.0855 shares of our common stock per $1,000 principal amount of the Convertible Notes, which was equivalent to an initial price of approximately $196.64 per share of our common stock. The conversion rate is subject to adjustment for certain events, including stock splits and issuance of certain stock dividends on our common stock. At June 30, 2024, the applicable conversion rate was 5.0862 shares of common stock per $1,000 principal amount of the Convertible Notes (equivalent to an adjusted conversion price of approximately $196.61 per share of common stock). Upon conversion, we will pay cash up to the aggregate principal amount of the Convertible Notes to be converted and pay or deliver, as the case may be, cash, shares of our common stock or a combination of cash and shares of our common stock, at our election, in respect of the remainder, if any, of our conversion obligation in excess of the aggregate principal amount of the Convertible Notes being converted. In addition, upon the occurrence of a "fundamental change" as defined in the indenture governing the Convertible Notes, holders may require us to repurchase for cash all or any portion of their Convertible Notes at a fundamental change repurchase price equal to 100% of the principal amount of the Convertible Notes to be repurchased plus any accrued and unpaid interest. If certain corporate events occur prior to the maturity date of the Convertible Notes or if we deliver a notice of redemption, we will, in certain circumstances, increase the conversion rate for a holder who elects to convert its Convertible Notes in connection with such event or notice of redemption. We will not be able to redeem the Convertible Notes prior to August 20, 2026. On or after August 20, 2026, we have the option to redeem for cash all or any portion of the Convertible Notes if the last reported sale price of our common stock is equal to or greater than 130% of the conversion price for a specified period of time at a redemption price equal to 100% of the principal amount of the Convertible Notes to be redeemed, plus any accrued but unpaid interest. In addition, as described in the indenture governing the Convertible Notes, certain events of default including, but not limited to, bankruptcy, insolvency or reorganization, may result in the Convertible Notes becoming due and payable immediately. Our net proceeds from the offering were approximately $560.5 million after deducting the initial purchasers’ discounts and commissions and offering expenses. We used approximately $51.8 million of the net proceeds to pay the cost of the Capped Call Transactions described below. We used the remaining net proceeds to repay all $185.0 million principal amount outstanding under our revolving credit facility, the remaining $234.4 million principal amount outstanding under our senior secured term loan due 2027 and approximately $89.4 million principal amount outstanding under our senior secured term loan due 2026. The Convertible Notes were recorded as a single unit within "Long-term debt" in our consolidated balance sheets as the conversion option within the Convertible Notes was not a derivative that would require bifurcation and the Convertible Notes did not involve a substantial premium. Transaction costs to issue the Convertible Notes were recorded as direct deductions from the related debt liabilities and are amortized to interest expense using the effective interest method over the terms of the Convertible Notes resulting in an effective annual interest rate of 2.79%. The net carrying amount of the Convertible Notes was as follows (in thousands): Balance at   June 30, 2024 October 1, 2023   Principal $ 575,000  $ 575,000  Unamortized discount and issuance costs (12,118) (14,158) Net carrying amount $ 562,882  $ 560,842  The following table sets forth the interest expense recognized related to the Convertible Notes for the third quarter and first nine months of fiscal 2024 (in thousands): Three Months Ended Nine Months Ended   June 30, 2024 June 30, 2024   Interest expense $ 3,234  $ 9,631  Amortization of discount and issuance costs 680  2,040  Total interest expense $ 3,914  $ 11,671  Concurrent with the offering of the Convertible Notes, in August 2023, we entered into the Capped Call Transactions. The Capped Call Transactions are expected generally to reduce the potential dilution of our common stock upon conversion of the Convertible Notes and/or offset any cash payments we elect to make in excess of the principal amount of converted Convertible Notes, as the case may be. If, however, the market price per share of our common stock, as measured under the terms of the Capped Call Transactions, exceeds the cap price of the Capped Call Transactions, there would nevertheless be dilution and/or there would not be an offset of such cash payments, in each case, to the extent that such market price exceeds the cap price of the Capped Call Transactions. The cap price of the Capped Call Transactions was initially $259.56 per share, which represented a premium of 65% over the last reported sale price of our common stock of $157.31 per share on the NASDAQ Global Select Market on August 17, 2023. The cap price is subject to adjustment for certain events, including stock splits and issuance of certain stock dividends on our common stock. At June 30, 2024, the adjusted cap price was approximately $259.53 per share. We recorded the Capped Call Transactions as separate transactions from the issuance of the Convertible Notes. The cost of $51.8 million incurred to purchase the Capped Call Transactions was recorded as a reduction to additional paid-in capital (net of $12.9 million in deferred taxes) on our consolidated balance sheet as of fiscal 2023 year-end. On October 26, 2022, we entered into a Third Amended and Restated Credit Agreement that provides for an additional $500 million senior secured term loan facility (the "New Term Loan Facility") increasing our total borrowing capacity to $1.55 billion. On January 23, 2023, we drew the entire amount of the New Term Loan Facility to partially finance the RPS acquisition. The New Term Loan Facility is not subject to any amortization payments of principal and matures on the third anniversary of the RPS acquisition closing date in January 2026. On February 18, 2022, we entered into Amendment No. 2 to Second Amended and Restated Credit Agreement (“Amended Credit Agreement”) with a total borrowing capacity of $1.05 billion that will mature in February 2027. The Amended Credit Agreement is a $750 million senior secured, five-year facility that provides for a $250 million term loan facility (the “Amended Term Loan Facility”) and a $500 million revolving credit facility (the “Amended Revolving Credit Facility”). In addition, the Amended Credit Agreement includes a $300 million accordion feature that allows us to increase the Amended Credit Agreement to $1.05 billion subject to lender approval. The Amended Credit Agreement provides for, among other things, (i) refinance indebtedness under our Credit Agreement dated at July 30, 2018; (ii) finance open market repurchases of common stock, acquisitions, and cash dividends and distributions; and (iii) utilize the proceeds for working capital, capital expenditures and other general corporate purposes. The Amended Credit Agreement provides for a reduction in the interest grid for meeting certain sustainability targets related to the (i) reduction of greenhouse gas emissions through the Company’s projects and operational sustainability initiatives and (ii) improvement of peoples’ lives as a result of the Company’s projects that provide environmental, social and governance benefits. The Amended Revolving Credit Facility includes a $100 million sublimit for the issuance of standby letters of credit, a $20 million sublimit for swingline loans and a $300 million sublimit for multicurrency borrowings and letters of credit. The entire Amended Term Loan Facility was drawn on February 18, 2022. We may borrow on the Amended Revolving Credit Facility, at our option, at either (a) a benchmark rate plus a margin that ranges from 1.000% to 1.875% per annum, or (b) a base rate for loans in U.S. dollars (the highest of the U.S. federal funds rate plus 0.50% per annum, the bank’s prime rate or the Secured Overnight Financing Rate ("SOFR") rate plus 1.00%, plus a margin that ranges from 0% to 0.875% per annum. In each case, the applicable margin is based on our Consolidated Leverage Ratio, calculated quarterly. The Amended Term Loan Facility is subject to the same interest rate provisions. The Amended Credit Agreement expires on February 18, 2027, or earlier at our discretion upon payment in full of loans and other obligations. At June 30, 2024, we had $300 million in outstanding borrowings under the Amended Credit Agreement, which was consisted of $300 million under the New Term Loan Facility and no borrowings under the Amended Revolving Credit Facility. During the nine months ended June 30, 2024, the weighted-average interest rate of the outstanding borrowings under the Amended Credit Agreement was 6.72%. In addition, we had $0.7 million in standby letters of credit under the Amended Credit Agreement. At June 30, 2024, we had $499.3 million of available credit under the Amended Revolving Credit Facility, all of which could be borrowed without a violation of our debt covenants. The Amended Credit Agreement contains certain affirmative and restrictive covenants, and customary events of default. The financial covenants provide for a maximum Consolidated Leverage Ratio of 3.25 to 1.00 (total funded debt/EBITDA, as defined in the Amended Credit Agreement) and a minimum Consolidated Interest Coverage Ratio of 3.00 to 1.00 (EBITDA/Consolidated Interest Charges, as defined in the Amended Credit Agreement). Our obligations under the Amended Credit Agreement are guaranteed by certain of our domestic subsidiaries and are secured by first priority liens on (i) the equity interests of certain of our subsidiaries, including those subsidiaries that are guarantors or borrowers under the Amended Credit Agreement, and (ii) the accounts receivable, general intangibles and intercompany loans and those of our subsidiaries that are guarantors or borrowers. At June 30, 2024, we were in compliance with these covenants with a consolidated leverage ratio of 1.51x and a consolidated interest coverage ratio of 12.47x. In addition to the Amended Credit Agreement, we maintain other credit facilities, which may be used for short-term cash advances and bank guarantees. At June 30, 2024, there were no outstanding borrowings under these facilities and the aggregate amount of standby letters of credit outstanding was $50.6 million. As of June 30, 2024, we had no bank overdrafts related to our disbursement bank accounts.

v3.24.2.u1

Derivative Financial Instruments	9 Months Ended
	Jun. 30, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments We periodically use certain interest rate derivative contracts to hedge interest rate exposures on our variable rate debt. We also enter into foreign currency derivative contracts with financial institutions to reduce the risk that cash flows and earnings could adversely be affected by foreign currency exchange rate fluctuations. Our hedging program is not designated for trading or speculative purposes. We recognize derivative instruments as either assets or liabilities on the accompanying consolidated balance sheets at fair value. We record changes in the fair value (i.e., gains or losses) of the derivatives that have been designated as cash flow hedges in our consolidated balance sheets as accumulated other comprehensive income, and in our consolidated statements of income for those derivatives designated as fair value hedges. Our derivative contracts are categorized within Level 2 of the fair value hierarchy. In the fourth quarter of fiscal 2022, we entered into a forward contract to acquire GBP 714.0 million at a rate of 1.0852 for a total of USD 774.8 million that was integrated with our plan to acquire RPS. This contract matured on December 30, 2022. On December 28, 2022, we entered into an extension of the integrated forward contract to acquire GBP 714.0 million at a rate of 1.086 for a total of USD 775.4 million, extending the maturity date to January 23, 2023, the closing date of the RPS acquisition. Although an effective economic hedge of our foreign exchange risk related to this transaction, the forward contract did not qualify for hedge accounting. As a result, the forward contract was marked-to-market with changes in fair value recognized in earnings each period. The intrinsic value of the forward contract was immaterial at inception as the GBP/USD spot and forward exchange rates were essentially the same. The fair value of the forward contract at October 2, 2022 was $19.9 million, and an unrealized gain of the same amount was recognized in our fourth quarter of fiscal 2022 results. On January 23, 2023, the forward contract was settled at the fair value of $109.3 million. We recognized additional gains of $68.0 million and $21.4 million in the first and second quarters of fiscal 2023, respectively. All gains related to this transaction were reported in “Other non-operating income" on our consolidated income statements for the respective periods. In fiscal 2018, we entered into five interest rate swap agreements that we designated as cash flow hedges to fix the interest rate on the borrowings under our term loan facility. The five swaps expired on July 31, 2023. The related loss of $1.0 million and $2.0 million were recognized and reported on our consolidated statement of comprehensive income for the three and nine months ended July 2, 2023. There were no derivative instruments that were not designated as hedging instruments for the first nine months of fiscal 2024 and 2023.

v3.24.2.u1

Reclassifications Out of Accumulated Other Comprehensive Income	9 Months Ended
	Jun. 30, 2024
Equity [Abstract]
Reclassifications Out of Accumulated Other Comprehensive Income	Reclassifications Out of Accumulated Other Comprehensive Income The accumulated balances and activities for the three and nine months ended June 30, 2024 and July 2, 2023 related to reclassifications out of accumulated other comprehensive income are summarized as follows (in thousands):   Three Months Ended   Foreign Currency Translation Adjustments Gain (Loss) on Derivative Instruments Net Pension Adjustments Accumulated Other Comprehensive Income (Loss)   Balance at April 2, 2023 $ (185,602) $ 1,427  $ 2,794  $ (181,381) Other comprehensive income (loss) before reclassifications 44,499  (2,137) —  42,362  Amounts reclassified from accumulated other comprehensive loss: Interest rate contracts, net of tax (1) —  1,093  —  1,093  Net current-period other comprehensive income (loss) 44,499  (1,044) —  43,455  Balance at July 2, 2023 $ (141,103) $ 383  $ 2,794  $ (137,926) Balance at March 31, 2024 $ (159,171) $ —  $ 2,625  $ (156,546) Other comprehensive income before reclassifications 1,854  —  3  1,857  Net current-period other comprehensive income 1,854  —  3  1,857  Balance at June 30, 2024 $ (157,317) $ —  $ 2,628  $ (154,689) Nine Months Ended Foreign Currency Translation Adjustments Gain (Loss) on Derivative Instruments Net Pension Adjustments Accumulated Other Comprehensive Income (Loss) Balance at October 2, 2022 $ (210,556) $ 2,412  —  $ (208,144) Other comprehensive income (loss) before reclassifications 69,453  (4,439) 2,794  67,808  Amounts reclassified from accumulated other comprehensive loss: Interest rate contracts, net of tax (1) —  2,410  —  2,410  Net current-period other comprehensive income (loss) 69,453  (2,029) 2,794  70,218  Balance at July 2, 2023 $ (141,103) $ 383  $ 2,794  $ (137,926) Balance at October 1, 2023 $ (197,933) $ —  $ 2,638  $ (195,295) Other comprehensive income (loss) before reclassifications 40,616  —  (10) 40,606  Net current-period other comprehensive income (loss) 40,616  —  (10) 40,606  Balance at June 30, 2024 $ (157,317) $ —  $ 2,628  $ (154,689) (1)    This accumulated other comprehensive component is reclassified to “Interest expense” in our consolidated statements of income. See Note 16 “Derivative Financial Instruments”, for more information.

v3.24.2.u1

Commitments and Contingencies	9 Months Ended
	Jun. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies We are subject to certain claims and lawsuits typically filed against the consulting and engineering profession, alleging primarily professional errors or omissions. We carry professional liability insurance, subject to certain deductibles and policy limits, against such claims. However, in some actions, parties are seeking damages that exceed our insurance coverage or for which we are not insured. While management does not believe that the resolution of these claims will have a material adverse effect, individually or in aggregate, on our financial position, results of operations or cash flows, management acknowledges the uncertainty surrounding the ultimate resolution of these matters. On July 15, 2019, following an initial January 14, 2019 filing, the Civil Division of the United States Attorney's Office filed an amended complaint in intervention in three qui tam actions filed against our subsidiary, Tetra Tech EC, Inc. ("TtEC"), in the U.S. District Court for the Northern District of California. The complaint alleges False Claims Act violations and breach of contract related to TtEC's contracts to perform environmental remediation services at the former Hunters Point Naval Shipyard in San Francisco, California. TtEC disputes the claims and will defend this matter vigorously. We are currently unable to determine the probability of the outcome of this matter or the range of reasonably possible loss, if any.

v3.24.2.u1

Related Party Transactions	9 Months Ended
	Jun. 30, 2024
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions We often provide services to unconsolidated joint ventures. The table below presents revenue and reimbursable costs related to services we provided to our unconsolidated joint ventures (in thousands):   Three Months Ended Nine Months Ended   June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023   Revenue $ 16,753  $ 22,373  $ 50,157  $ 65,249  Related reimbursable costs 15,287  20,848  46,025  61,475  Our consolidated balance sheets also included the following amounts related to these services (in thousands): Balance at June 30, 2024 October 1, 2023 Accounts receivable, net $ 14,305  $ 19,944  Contract assets 1,997  2,723  Contract liabilities (3,708) (3,158)

v3.24.2.u1

Subsequent Events	9 Months Ended
	Jun. 30, 2024
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On July 29, 2024, our Board of Directors declared a quarterly cash dividend of $0.29 per share payable on August 30, 2024 to stockholders of record as of the close of business on August 15, 2024. On July 29, 2024, our Board of Directors also approved a five-for-one stock split of our common stock. The split will be effected through an amendment to our Restated Certificate of Incorporation, which will result in a proportionate increase in the number of shares of authorized common stock. The stock split is intended to make shares more accessible to a broader base of investors and enhance liquidity in the trading of Tetra Tech’s shares. Each record holder of common stock as of the close of market on September 5, 2024, will receive four additional shares of common stock. The stock split is expected to be effective after close of trading on September 6, 2024. Trading is expected to commence on a split-adjusted basis at market open on September 9, 2024. The following table reflects basic and diluted weighted average shares and net income per share on an unaudited pro forma basis giving effect to the stock split as if it had been effective for all periods presented: Pro Forma (Unaudited)   Three Months Ended Nine Months Ended   June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023   Net income attributable to Tetra Tech $ 85,810  $ 60,235  $ 237,228  $ 219,771  Weighted-average common shares outstanding - basic 267,575  266,155  267,255  265,940  Effect of dilutive stock options and unvested restricted stock 2,165  2,110  2,075  2,135  Shares issuable assuming conversion of convertible notes 520  —  175  —  Weighted-average common shares outstanding - diluted 270,260  268,265  269,505  268,075  Earnings per share attributable to Tetra Tech: Basic $ 0.32  $ 0.23  $ 0.89  $ 0.83  Diluted $ 0.32  $ 0.22  $ 0.88  $ 0.82  This forward stock split will trigger adjustments to the share-based ratios related to our Convertible Notes and Capped Call Transactions, see Note 15, “Long-Term Debt” of the “Notes to Consolidated Financial Statements”.

v3.24.2.u1

Insider Trading Arrangements	3 Months Ended
	Jun. 30, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

v3.24.2.u1

Recent Accounting Pronouncements (Policies)	9 Months Ended
	Jun. 30, 2024
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	In November 2023, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update (“ASU”) No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which requires that an entity report segment information in accordance with Topic 280, Segment Reporting. The amendments in the ASU are intended to improve reportable segment disclosure requirements primarily through enhanced disclosures about significant segment expenses. The amendments in this ASU are effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024 (fiscal 2025 for us). Early adoption is permitted. We are currently evaluating the impact of this guidance on our consolidated financial statements; however, we do not plan to adopt Topic 280 before fiscal 2025. In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which requires that an entity, on an annual basis, disclose additional income tax information, primarily related to the rate reconciliation and income taxes paid. The amendments in the ASU are intended to enhance the transparency and decision usefulness of income tax disclosures. The amendments in this ASU are effective for annual periods beginning after December 15, 2024 (fiscal 2026 for us). Early adoption is permitted. We are currently evaluating the impact of this guidance on our consolidated financial statements; however, we do not plan to adopt Topic 740 before fiscal 2026.
Contract Assets and Contract Liabilities	We invoice customers based on the contractual terms of each contract. However, the timing of revenue recognition may differ from the timing of invoice issuance. Contract assets represent revenue recognized in excess of the amounts for which we have the contractual right to bill our customers. Such amounts are recoverable from customers based upon various measures of performance, including achievement of certain milestones or completion of a contract. In addition, many of our time-and-materials arrangements are billed in arrears pursuant to contract terms that are standard within the industry, resulting in contract assets and/or unbilled receivables being recorded, as revenue is recognized in advance of billings. Contract retentions, included in contract assets, represent amounts withheld by clients until certain conditions are met or the project is completed, which may extend beyond one year. Contract liabilities consist of billings in excess of revenue recognized. Contract liabilities decrease as we recognize revenue from the satisfaction of the related performance obligation and increase as billings in advance of revenue recognition occur. Contract assets and liabilities are reported in a net position on a contract-by-contract basis at the end of each reporting period. There were no substantial non-current contract assets or liabilities for the periods presented. Our RUPO represents a measure of the total dollar value of work to be performed on contracts awarded and in progress. We had $5.2 billion of RUPO at June 30, 2024. Our RUPO increases with awards from new contracts or additions on existing contracts, and decreases as work is performed and revenue is recognized on existing contracts. Our RUPO may also decrease when projects are canceled or modified in scope. We include a contract within our RUPO when the contract is awarded and an agreement on contract terms has been reached. Although RUPO reflects business that is considered to be firm, cancellations, deferrals or scope adjustments may occur. Our RUPO is adjusted to reflect any known project cancellations, revisions to project scope and cost, foreign currency exchange fluctuations and project deferrals, as appropriate. Our operations and maintenance contracts can generally be terminated by the clients without a substantive financial penalty; therefore, the remaining performance obligations on such contracts are limited to the notice period required for the termination (usually 30, 60, or 90 days).
Accounts Receivable, Net	Billed accounts receivable represent amounts billed to clients that have not been collected. Unbilled accounts receivable, which represent an unconditional right to payment subject only to the passage of time, include unbilled amounts typically resulting from revenue recognized but not yet billed pursuant to contract terms or billed after the period end date. Substantially all of our unbilled receivables at June 30, 2024 are expected to be billed and collected within 12 months. The allowance for doubtful accounts represents amounts that are expected to become uncollectible or unrealizable in the future. We determine an estimated allowance for uncollectible accounts based on management's consideration of trends in the actual and forecasted credit quality of our clients, including delinquency and payment history; type of client, such as a government agency or a commercial sector client; and general economic and industry conditions, which may affect our clients' ability to pay.
Fair Value Measurement	We classified our assets and liabilities that were carried at fair value in one of the following categories: •Level 1: Quoted market prices in active markets for identical assets or liabilities. •Level 2: Observable market-based inputs or unobservable inputs that are corroborated by market data. •Level 3: Unobservable inputs that are not corroborated by market data. Derivative Instruments. Our derivative instruments are categorized within Level 2 of the fair value hierarchy. For additional information about our derivative financial instruments (see Note 16, "Derivative Financial Instruments"). Contingent Consideration. We measure our contingent earn-out liabilities at fair value on a recurring basis using significant unobservable inputs classified within Level 3 of the fair value hierarchy. (see Note 4, "Acquisitions" for further information). Debt. The fair value of long-term debt under our Credit Facility was determined using the present value of future cash flows based on the borrowing rates currently available for debt with similar terms and maturities (Level 2 measurement, as described in “Critical Accounting Policies and Estimates” in our Annual Report on Form 10-K for the fiscal year ended October 1, 2023). The carrying value of our long-term debt under our Credit Facility approximated fair value at June 30, 2024 and October 1, 2023.

v3.24.2.u1

Revenue and Contract Balances (Tables)	9 Months Ended
	Jun. 30, 2024
Revenue from Contract with Customer [Abstract]
Summary of revenue disaggregated by client sector and contract type	The following tables present our revenue disaggregated by client sector and contract type (in thousands):   Three Months Ended Nine Months Ended   June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023 Client Sector:     U.S. federal government (1) $ 432,242  $ 338,022  $ 1,221,320  $ 996,471  U.S. state and local government 146,401  151,462  444,877  452,447  U.S. commercial 241,838  225,907  665,675  633,401  International (2) 523,842  493,556  1,492,333  1,179,619  Total $ 1,344,323  $ 1,208,947  $ 3,824,205  $ 3,261,938  Contract Type: Fixed-price $ 548,452  $ 452,605  $ 1,478,915  $ 1,194,266  Time-and-materials 589,301  596,904  1,730,796  1,550,970  Cost-plus 206,570  159,438  614,494  516,702  Total $ 1,344,323  $ 1,208,947  $ 3,824,205  $ 3,261,938  (1)    Includes revenue generated under U.S. federal government contracts performed outside the United States. (2)    Includes revenue generated from non-U.S. clients, primarily in Canada, Australia, Europe and the United Kingdom.
Summary of net contract assets/liabilities	Net contract assets/liabilities consisted of the following (in thousands): Balance at June 30, 2024 October 1, 2023 Contract assets (1) $ 118,556  $ 113,939  Contract liabilities (372,283) (335,044) Net contract liabilities $ (253,727) $ (221,105) (1)    Includes $6.2 million and $6.8 million of contract retentions at June 30, 2024 and October 1, 2023, respectively.
Components of net accounts receivable	Net accounts receivable consisted of the following (in thousands): Balance at   June 30, 2024 October 1, 2023 Billed $ 685,184  $ 672,712  Unbilled 372,913  306,788  Total accounts receivable 1,058,097  979,500  Allowance for doubtful accounts (4,339) (4,965) Total accounts receivable, net $ 1,053,758  $ 974,535
Remaining performance obligation, expected timing	We expect to satisfy our RUPO at June 30, 2024 over the following periods (in thousands): Amount Within 12 months $ 3,508,571  Beyond 1,683,295  Total $ 5,191,866

v3.24.2.u1

Acquisitions (Tables)	9 Months Ended
	Jun. 30, 2024
Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]
Schedule of recognized identified assets acquired and liabilities assumed	The table below represents the purchase price allocation for RPS based on estimates, assumptions, valuations and other analyses as of January 23, 2023. The all cash purchase consideration, excluding the aforementioned forward contract gain, was allocated to the tangible and intangible assets, and liabilities of RPS based on their estimated fair values, with any excess purchase consideration allocated to goodwill as follows (in thousands): Amount Cash and cash equivalents $ 32,093  Accounts receivable and contract assets 202,303  Prepaid expenses and other current assets 45,999  Income taxes receivables 1,999  Property and equipment 38,435  Right-of-use assets, operating leases 40,179  Intangible assets 174,094  Deferred income taxes 35,084  Other long-term assets 1,061  Total assets acquired 571,247  Accounts payable $ (44,376) Accrued compensation (19,073) Contract liabilities (46,287) Income tax payable (7,083) Short-term lease liabilities, operating leases (13,477) Other current liabilities (135,474) Current portion of long-term debt (91,973) Long-term lease liabilities, operating leases (26,702) Other long-term liabilities (13,742) Deferred tax liabilities (41,613) Total liabilities assumed (439,800) Fair value of net assets acquired 131,447  Goodwill 652,762  Total purchase consideration $ 784,209
Schedule of acquired finite-lived intangible assets by major class	The following table summarizes the estimated fair values that were assigned to intangible assets at the acquisition date: Fair Value Weighted-Average Estimated Useful Life (in thousands) (in years) Backlog $ 27,880  1.6 Trade names 27,260  3.0 Client relations 118,954  11.1 Total intangible assets acquired $ 174,094  8.3
Business acquisition, pro forma information	Following are the supplemental consolidated financial results of Tetra Tech and RPS for the third quarter and first nine months of fiscal 2023 on an unaudited pro forma basis, as if the RPS acquisition had been consummated at the beginning of fiscal 2023 (in thousands): Three Months Ended Nine Months Ended July 2, 2023 July 2, 2023 Revenue $ 1,208,947  $ 3,519,792  Net income including noncontrolling interests 61,770  104,564
Schedule of estimated contingent earn out liabilities	The following table summarizes the changes in the fair value of estimated contingent consideration (in thousands): Three Months Ended Nine Months Ended   June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023 Beginning balance $ 74,579  $ 88,082  $ 73,422  $ 65,566  Estimated earn-out liabilities for acquisitions 1,138  —  23,038  12,248  Payments of contingent consideration (7,000) (13,078) (29,112) (15,078) Adjustments to fair value recorded in earnings 500  —  477  8,477  Interest accretion expense 1,038  707  1,953  1,919  Effect of foreign currency exchange rate changes 28  888  505  3,467  Ending balance $ 70,283  $ 76,599  $ 70,283  $ 76,599  Maximum potential payout at end of period $ 128,573  $ 120,320  $ 128,573  $ 120,320

v3.24.2.u1

Goodwill and Intangible Assets (Tables)	9 Months Ended
	Jun. 30, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of changes in the carrying value of goodwill	The following table summarizes the changes in the carrying value of goodwill by reportable segment (in thousands):   GSG CIG Total Balance at October 1, 2023 $ 659,942  $ 1,220,302  $ 1,880,244  Acquisition activity 84,865  —  84,865  Translation and other adjustments 2,282  24,719  27,001  Balance at June 30, 2024 $ 747,089  $ 1,245,021  $ 1,992,110
Summary of acquired identifiable intangible assets with finite useful lives	The following table presents the gross amount and accumulated amortization of our acquired identifiable intangible assets with finite useful lives included in “Intangible assets, net” on the consolidated balance sheets ($ in thousands): Period Ended   June 30, 2024 October 1, 2023   Weighted- Average Remaining Life (in Years) Gross Amount Accumulated Amortization Net Amount Gross Amount Accumulated Amortization Net Amount   Client relations 8.4 $ 190,329  $ (50,980) $ 139,349  $ 169,217  $ (36,072) $ 133,145  Backlog 0.6 72,579  (65,050) 7,529  63,825  (47,802) 16,023  Trade names 1.7 38,773  (21,192) 17,581  37,411  (12,643) 24,768  Total   $ 301,681  $ (137,222) $ 164,459  $ 270,453  $ (96,517) $ 173,936
Estimated amortization expense for the remainder of the fiscal year and the succeeding years	Estimated amortization expense for the remainder of fiscal 2024 and succeeding years is as follows (in thousands):   Amount   2024 (remaining) $ 11,322  2025 34,712  2026 23,334  2027 16,830  2028 16,320  Beyond 61,941  Total $ 164,459

v3.24.2.u1

Property and Equipment (Tables)	9 Months Ended
	Jun. 30, 2024
Property, Plant and Equipment [Abstract]
Schedule of components of property and equipment	Property and equipment consisted of the following (in thousands): Balance at   June 30, 2024 October 1, 2023   Equipment, furniture and fixtures $ 130,748  $ 132,744  Leasehold improvements 46,042  44,733  Total property and equipment 176,790  177,477  Accumulated depreciation (106,096) (102,645) Property and equipment, net $ 70,694  $ 74,832

v3.24.2.u1

Stock Repurchase and Dividends (Tables)	9 Months Ended
	Jun. 30, 2024
Stock Repurchase And Dividends [Abstract]
Summary of dividends declared and paid	The following table presents dividends declared and paid in the first nine months of fiscal 2024 and 2023: Declare Date Dividend Paid Per Share Record Date Payment Date Dividend Paid (in thousands) November 13, 2023 $ 0.26  November 30, 2023 December 13, 2023 $ 13,873  January 29, 2024 0.26  February 14, 2024 February 27, 2024 13,908  April 29, 2024 0.29  May 20, 2024 May 31, 2024 15,522  Total dividend paid as of June 30, 2024 $ 43,303  November 7, 2022 $ 0.23  November 21, 2022 December 9, 2022 $ 12,186  January 30, 2023 0.23  February 13, 2023 February 24, 2023 12,242  May 8, 2023 0.26  May 24, 2023 June 6, 2023 13,840  Total dividend paid as of July 2, 2023 $ 38,268

v3.24.2.u1

Leases (Tables)	9 Months Ended
	Jun. 30, 2024
Leases [Abstract]
Summary of components of lease cost	The components of lease costs are as follows (in thousands): Three Months Ended Nine Months Ended June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023 Operating lease cost $ 24,562  $ 24,775  $ 73,580  $ 70,155  Sublease income (184) (46) (347) (125) Total lease cost $ 24,378  $ 24,729  $ 73,233  $ 70,030  Supplemental cash flow information related to leases is as follows (in thousands): Nine Months Ended June 30, 2024 July 2, 2023 Operating cash flows for operating leases $ 56,379  $ 57,871  Right-of-use assets obtained in exchange for new operating lease liabilities 38,160  72,294
Summary of supplemental balance sheet and other information	Supplemental balance sheet and other information related to leases are as follows (in thousands): Balance at June 30, 2024 October 1, 2023 Operating leases: Right-of-use assets $ 167,317  $ 175,932  Lease liabilities: Current 65,932  65,005  Non-current 128,892  144,685  Total operating lease liabilities $ 194,824  $ 209,690  Weighted-average remaining lease term: Operating leases 4 years 5 years Weighted-average discount rate: Operating leases 3.4  % 3.0  %
Summary of maturity of future undiscounted cash flows associated with operating lease liabilities	A maturity analysis of the future undiscounted cash flows associated with our lease liabilities at June 30, 2024 is as follows (in thousands): Operating Leases 2024 (remaining) $ 20,124  2025 65,068  2026 44,638  2027 31,231  2028 20,176  Beyond 28,412  Total lease payments 209,649   Less: imputed interest (14,825) Total present value of lease liabilities $ 194,824

v3.24.2.u1

Earnings per Share ("EPS") (Tables)	9 Months Ended
	Jun. 30, 2024
Earnings Per Share [Abstract]
Schedule of number of weighted-average shares used to compute basic and diluted EPS	The following table presents the number of weighted-average shares used to compute basic and diluted EPS (in thousands, except per share data):   Three Months Ended Nine Months Ended   June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023   Net income attributable to Tetra Tech $ 85,810  $ 60,235  $ 237,228  $ 219,771  Weighted-average common shares outstanding – basic 53,515  53,231  53,451  53,188  Effect of dilutive stock options and unvested restricted stock 433  422  415  427  Shares issuable assuming conversion of convertible notes 104  —  35  —  Weighted-average common shares outstanding – diluted 54,052  53,653  53,901  53,615  Earnings per share attributable to Tetra Tech:         Basic $ 1.60  $ 1.13  $ 4.44  $ 4.13  Diluted $ 1.59  $ 1.12  $ 4.40  $ 4.10

v3.24.2.u1

Reportable Segments (Tables)	9 Months Ended
	Jun. 30, 2024
Segment Reporting [Abstract]
Summarized financial information of reportable segments	The following tables summarize financial information regarding our reportable segments (in thousands):   Three Months Ended Nine Months Ended   June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023   Revenue         GSG $ 640,553  $ 531,050  $ 1,812,721  $ 1,565,371  CIG 723,617  691,386  2,063,879  1,741,300  Elimination of inter-segment revenue (19,847) (13,489) (52,395) (44,733) Total revenue $ 1,344,323  $ 1,208,947  $ 3,824,205  $ 3,261,938  Income from operations         GSG $ 71,518  $ 54,496  $ 198,652  $ 167,053  CIG 86,465  69,572  233,821  172,199  Corporate (1) (29,353) (26,393) (75,078) (88,516) Total income from operations $ 128,630  $ 97,675  $ 357,395  $ 250,736  (1)     Includes amortization of intangibles, acquisition and integration expenses, as well as other costs and other income not allocable to our reportable segments. Balance at   June 30, 2024 October 1, 2023   Total Assets     GSG $ 632,346  $ 543,066  CIG 1,066,241  994,470  Corporate (1) 2,386,318  2,282,941  Total assets $ 4,084,905  $ 3,820,477  (1)    Corporate assets consist of intercompany eliminations and assets not allocated to our reportable segments including goodwill, intangible assets, deferred income taxes and certain other assets.

v3.24.2.u1

Long-Term Debt (Tables)	9 Months Ended
	Jun. 30, 2024
Debt Disclosure [Abstract]
Schedule of long-term debt instruments	Long-term debt consisted of the following (in thousands): Balance at   June 30, 2024 October 1, 2023   Credit facilities $ 300,000  $ 320,000  Convertible notes 575,000  575,000  Debt issuance costs and discount (13,170) (15,471) Long-term debt $ 861,830  $ 879,529
Convertible debt	The net carrying amount of the Convertible Notes was as follows (in thousands): Balance at   June 30, 2024 October 1, 2023   Principal $ 575,000  $ 575,000  Unamortized discount and issuance costs (12,118) (14,158) Net carrying amount $ 562,882  $ 560,842
Interest income and interest expense disclosure	The following table sets forth the interest expense recognized related to the Convertible Notes for the third quarter and first nine months of fiscal 2024 (in thousands): Three Months Ended Nine Months Ended   June 30, 2024 June 30, 2024   Interest expense $ 3,234  $ 9,631  Amortization of discount and issuance costs 680  2,040  Total interest expense $ 3,914  $ 11,671

v3.24.2.u1

Reclassifications Out of Accumulated Other Comprehensive Income (Tables)	9 Months Ended
	Jun. 30, 2024
Equity [Abstract]
Summary of reclassifications out of accumulated other comprehensive income	The accumulated balances and activities for the three and nine months ended June 30, 2024 and July 2, 2023 related to reclassifications out of accumulated other comprehensive income are summarized as follows (in thousands):   Three Months Ended   Foreign Currency Translation Adjustments Gain (Loss) on Derivative Instruments Net Pension Adjustments Accumulated Other Comprehensive Income (Loss)   Balance at April 2, 2023 $ (185,602) $ 1,427  $ 2,794  $ (181,381) Other comprehensive income (loss) before reclassifications 44,499  (2,137) —  42,362  Amounts reclassified from accumulated other comprehensive loss: Interest rate contracts, net of tax (1) —  1,093  —  1,093  Net current-period other comprehensive income (loss) 44,499  (1,044) —  43,455  Balance at July 2, 2023 $ (141,103) $ 383  $ 2,794  $ (137,926) Balance at March 31, 2024 $ (159,171) $ —  $ 2,625  $ (156,546) Other comprehensive income before reclassifications 1,854  —  3  1,857  Net current-period other comprehensive income 1,854  —  3  1,857  Balance at June 30, 2024 $ (157,317) $ —  $ 2,628  $ (154,689) Nine Months Ended Foreign Currency Translation Adjustments Gain (Loss) on Derivative Instruments Net Pension Adjustments Accumulated Other Comprehensive Income (Loss) Balance at October 2, 2022 $ (210,556) $ 2,412  —  $ (208,144) Other comprehensive income (loss) before reclassifications 69,453  (4,439) 2,794  67,808  Amounts reclassified from accumulated other comprehensive loss: Interest rate contracts, net of tax (1) —  2,410  —  2,410  Net current-period other comprehensive income (loss) 69,453  (2,029) 2,794  70,218  Balance at July 2, 2023 $ (141,103) $ 383  $ 2,794  $ (137,926) Balance at October 1, 2023 $ (197,933) $ —  $ 2,638  $ (195,295) Other comprehensive income (loss) before reclassifications 40,616  —  (10) 40,606  Net current-period other comprehensive income (loss) 40,616  —  (10) 40,606  Balance at June 30, 2024 $ (157,317) $ —  $ 2,628  $ (154,689) (1)    This accumulated other comprehensive component is reclassified to “Interest expense” in our consolidated statements of income. See Note 16 “Derivative Financial Instruments”, for more information.

v3.24.2.u1

Related Party Transactions (Tables)	9 Months Ended
	Jun. 30, 2024
Related Party Transactions [Abstract]
Schedule of related party transactions	We often provide services to unconsolidated joint ventures. The table below presents revenue and reimbursable costs related to services we provided to our unconsolidated joint ventures (in thousands):   Three Months Ended Nine Months Ended   June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023   Revenue $ 16,753  $ 22,373  $ 50,157  $ 65,249  Related reimbursable costs 15,287  20,848  46,025  61,475  Our consolidated balance sheets also included the following amounts related to these services (in thousands): Balance at June 30, 2024 October 1, 2023 Accounts receivable, net $ 14,305  $ 19,944  Contract assets 1,997  2,723  Contract liabilities (3,708) (3,158)

v3.24.2.u1

Subsequent Events (Tables)	9 Months Ended
	Jun. 30, 2024
Subsequent Events [Abstract]
Schedule of Proforma	The following table reflects basic and diluted weighted average shares and net income per share on an unaudited pro forma basis giving effect to the stock split as if it had been effective for all periods presented: Pro Forma (Unaudited)   Three Months Ended Nine Months Ended   June 30, 2024 July 2, 2023 June 30, 2024 July 2, 2023   Net income attributable to Tetra Tech $ 85,810  $ 60,235  $ 237,228  $ 219,771  Weighted-average common shares outstanding - basic 267,575  266,155  267,255  265,940  Effect of dilutive stock options and unvested restricted stock 2,165  2,110  2,075  2,135  Shares issuable assuming conversion of convertible notes 520  —  175  —  Weighted-average common shares outstanding - diluted 270,260  268,265  269,505  268,075  Earnings per share attributable to Tetra Tech: Basic $ 0.32  $ 0.23  $ 0.89  $ 0.83  Diluted $ 0.32  $ 0.22  $ 0.88  $ 0.82

v3.24.2.u1

Revenue and Contract Balances - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 1,344,323	$ 1,208,947	$ 3,824,205	$ 3,261,938
Fixed-price
Disaggregation of Revenue [Line Items]
Revenue	548,452	452,605	1,478,915	1,194,266
Time-and-materials
Disaggregation of Revenue [Line Items]
Revenue	589,301	596,904	1,730,796	1,550,970
Cost-plus
Disaggregation of Revenue [Line Items]
Revenue	206,570	159,438	614,494	516,702
U.S. federal government
Disaggregation of Revenue [Line Items]
Revenue	432,242	338,022	1,221,320	996,471
U.S. state and local government
Disaggregation of Revenue [Line Items]
Revenue	146,401	151,462	444,877	452,447
U.S. commercial
Disaggregation of Revenue [Line Items]
Revenue	241,838	225,907	665,675	633,401
International
Disaggregation of Revenue [Line Items]
Revenue	$ 523,842	$ 493,556	$ 1,492,333	$ 1,179,619

v3.24.2.u1

Revenue and Contract Balances - Summary of Contract Liabilities/Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Oct. 01, 2023
Disaggregation of Revenue [Line Items]
Contract assets	$ 118,556	$ 113,939
Contract liabilities	(372,283)	(335,044)
Net contract liabilities	(253,727)	(221,105)
Contract Retentions
Disaggregation of Revenue [Line Items]
Contract assets	$ 6,200	$ 6,800

v3.24.2.u1

Revenue and Contract Balances - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Jun. 30, 2024	Jun. 30, 2024	Jul. 02, 2023	Oct. 01, 2023
Revenue from Contract with Customer [Abstract]
Contract liability revenue recognized during the period		$ 214,000	$ 143,000
Net favorable (unfavorable) revenue and operating income adjustments	$ 6,500	16,400	$ 4,000
Liabilities for anticipated losses	15,000	15,000		$ 8,500
Estimated cost to complete the related contracts	95,000	$ 95,000		$ 68,000
Period for billing and collecting unbilled receivables		12 months
Remaining unsatisfied performance obligation	$ 5,191,866	$ 5,191,866
Remaining performance obligation, termination notice period one		30 days
Remaining performance obligation, termination notice period two		60 days
Remaining performance obligation, termination notice period three		90 days

v3.24.2.u1

Revenue and Contract Balances - Accounts Receivable, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Oct. 01, 2023
Revenue from Contract with Customer [Abstract]
Billed	$ 685,184	$ 672,712
Unbilled	372,913	306,788
Total accounts receivable	1,058,097	979,500
Allowance for doubtful accounts	(4,339)	(4,965)
Total accounts receivable, net	$ 1,053,758	$ 974,535

v3.24.2.u1

Revenue and Contract Balances - Remaining Unsatisfied Performance Obligations (Details) $ in Thousands	Jun. 30, 2024 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining unsatisfied performance obligation	$ 5,191,866
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining unsatisfied performance obligation	$ 3,508,571
Remaining unsatisfied performance obligation, expected timing of satisfaction	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining unsatisfied performance obligation	$ 1,683,295
Remaining unsatisfied performance obligation, expected timing of satisfaction

v3.24.2.u1

Acquisitions - Narrative (Details) £ / shares in Units, $ in Thousands, £ in Millions			3 Months Ended			9 Months Ended		12 Months Ended
	Jan. 23, 2023 USD ($) employee	Jan. 23, 2023 GBP (£) employee	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Jul. 02, 2023 USD ($)	Jun. 30, 2024 USD ($)	Jul. 02, 2023 USD ($)	Oct. 01, 2023 USD ($) employee program	Oct. 02, 2022 USD ($)	Sep. 23, 2022 £ / shares
Business Acquisition [Line Items]
Goodwill			$ 1,992,110			$ 1,992,110		$ 1,880,244
Acquisition and integration expenses			0		$ 2,107	0	$ 25,812
Reduction in contingent earn-out liabilities			$ 0			$ 0	8,500
Minimum
Business Acquisition [Line Items]
Significant unobservable input, earn-out period						3 years
Minimum | Existing customer contracts
Business Acquisition [Line Items]
Useful life of intangible assets			1 year			1 year
Maximum
Business Acquisition [Line Items]
Significant unobservable input, earn-out period						5 years
Maximum | Existing customer contracts
Business Acquisition [Line Items]
Useful life of intangible assets			12 years			12 years
LS Technologies
Business Acquisition [Line Items]
Total purchase price				$ 120,000
Initial cash payments				93,000
Cash holdback related to tax reserve				4,000
Intangible assets				23,000
Equity interests issued and issuable				23,000
Net tangible assets				12,000
Goodwill				85,000
LS Technologies | Maximum
Business Acquisition [Line Items]
Equity interests issued and issuable				$ 60,000
RPS Group PLC
Business Acquisition [Line Items]
Total purchase price	$ 784,000	£ 633
Intangible assets	174,094
Goodwill	$ 652,762
Pence per share expected to be acquired | £ / shares										£ 2.22
Number of employees | employee	5,000	5,000
Acquisition and integration expenses					$ 2,100		$ 25,800
Net purchase price	$ 675,000
RPS Group PLC | Foreign Exchange Forward
Business Acquisition [Line Items]
Foreign currency forward contract, asset fair value	$ 109,300								$ 19,900
Amyx, Inc.
Business Acquisition [Line Items]
Total purchase price								$ 120,900
Number of employees | employee								500
Number of government programs acquired | program								30
Payables related to promissory note								$ 100,000
Receivables (payables) related to estimated post-closing adjustments								8,700
Contingent earn-out liability								12,200
Aggregate maximum of contingent consideration								$ 25,000

v3.24.2.u1

Acquisitions - Schedule of Purchase Price Allocation (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Oct. 01, 2023	Jan. 23, 2023
Business Acquisition [Line Items]
Goodwill	$ 1,992,110	$ 1,880,244
RPS Group PLC
Business Acquisition [Line Items]
Cash and cash equivalents			$ 32,093
Accounts receivable and contract assets			202,303
Prepaid expenses and other current assets			45,999
Income taxes receivables			1,999
Property and equipment			38,435
Right-of-use assets, operating leases			40,179
Intangible assets			174,094
Deferred income taxes			35,084
Other long-term assets			1,061
Total assets acquired			571,247
Accounts payable			(44,376)
Accrued compensation			(19,073)
Contract liabilities			(46,287)
Income tax payable			(7,083)
Short-term lease liabilities, operating leases			(13,477)
Other current liabilities			(135,474)
Current portion of long-term debt			(91,973)
Long-term lease liabilities, operating leases			(26,702)
Other long-term liabilities			(13,742)
Deferred tax liabilities			(41,613)
Total liabilities assumed			(439,800)
Fair value of net assets acquired			131,447
Goodwill			652,762
Total purchase consideration			$ 784,209

v3.24.2.u1

Acquisitions - Schedule of Intangible Assets Assumed (Details) - USD ($) $ in Thousands		9 Months Ended
	Jan. 23, 2023	Jun. 30, 2024
Backlog
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average Amortization Period (in years)		7 months 6 days
Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average Amortization Period (in years)		1 year 8 months 12 days
Client relations
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted-average Amortization Period (in years)		8 years 4 months 24 days
RPS Group PLC
Acquired Finite-Lived Intangible Assets [Line Items]
Fair Value	$ 174,094
Weighted-average Amortization Period (in years)	8 years 3 months 18 days
RPS Group PLC | Backlog
Acquired Finite-Lived Intangible Assets [Line Items]
Fair Value	$ 27,880
Weighted-average Amortization Period (in years)	1 year 7 months 6 days
RPS Group PLC | Trade names
Acquired Finite-Lived Intangible Assets [Line Items]
Fair Value	$ 27,260
Weighted-average Amortization Period (in years)	3 years
RPS Group PLC | Client relations
Acquired Finite-Lived Intangible Assets [Line Items]
Fair Value	$ 118,954
Weighted-average Amortization Period (in years)	11 years 1 month 6 days

v3.24.2.u1

Acquisitions - Supplemental Pro Forma Information (Details) - RPS Group PLC - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Jul. 02, 2023	Jul. 02, 2023
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Revenue	$ 1,208,947	$ 3,519,792
Net income including noncontrolling interests	$ 61,770	$ 104,564

v3.24.2.u1

Acquisitions - Schedule of Estimated Contingent Consideration (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023
All acquisitions
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Aggregate maximum of contingent consideration	$ 128,573	$ 120,320	$ 128,573	$ 120,320
Contingent Consideration
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	74,579	88,082	73,422	65,566
Estimated earn-out liabilities for acquisitions	1,138	0	23,038	12,248
Payments of contingent consideration	(7,000)	(13,078)	(29,112)	(15,078)
Adjustments to fair value recorded in earnings	500	0	477	8,477
Interest accretion expense	1,038	707	1,953	1,919
Effect of foreign currency exchange rate changes	28	888	505	3,467
Ending balance	$ 70,283	$ 76,599	$ 70,283	$ 76,599

v3.24.2.u1

Goodwill and Intangible Assets - Goodwill (Details) $ in Thousands	9 Months Ended
	Jun. 30, 2024 USD ($)
Goodwill
Balance at beginning of the period	$ 1,880,244
Acquisition activity	84,865
Translation and other adjustments	27,001
Balance at end of the period	1,992,110
GSG
Goodwill
Balance at beginning of the period	659,942
Acquisition activity	84,865
Translation and other adjustments	2,282
Balance at end of the period	747,089
CIG
Goodwill
Balance at beginning of the period	1,220,302
Acquisition activity	0
Translation and other adjustments	24,719
Balance at end of the period	$ 1,245,021

v3.24.2.u1

Goodwill and Intangible Assets - Narrative (Details) - USD ($)		3 Months Ended		9 Months Ended
	Jul. 03, 2023	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023	Oct. 01, 2023
Goodwill [Line Items]
Impairment of goodwill	$ 0
Percentage of excess of fair value over carrying value (less than)	45.00%
Amortization expense		$ 13,800,000	$ 14,100,000	$ 38,400,000	$ 29,600,000
GSG
Goodwill [Line Items]
Gross amounts of goodwill		764,800,000		764,800,000		$ 677,600,000
Accumulated impairment		17,700,000		17,700,000		17,700,000
CIG
Goodwill [Line Items]
Gross amounts of goodwill		1,366,500,000		1,366,500,000		1,341,800,000
Accumulated impairment		$ 121,500,000		$ 121,500,000		$ 121,500,000

v3.24.2.u1

Goodwill and Intangible Assets - Gross Amount and Accumulated Amortization of Acquired Finite-lived Intangibles (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2024	Oct. 01, 2023
Finite-Lived Intangible Assets [Line Items]
Gross Amount	$ 301,681	$ 270,453
Accumulated Amortization	(137,222)	(96,517)
Net Amount	$ 164,459	173,936
Client relations
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in Years)	8 years 4 months 24 days
Gross Amount	$ 190,329	169,217
Accumulated Amortization	(50,980)	(36,072)
Net Amount	$ 139,349	133,145
Backlog
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in Years)	7 months 6 days
Gross Amount	$ 72,579	63,825
Accumulated Amortization	(65,050)	(47,802)
Net Amount	$ 7,529	16,023
Trade names
Finite-Lived Intangible Assets [Line Items]
Weighted- Average Remaining Life (in Years)	1 year 8 months 12 days
Gross Amount	$ 38,773	37,411
Accumulated Amortization	(21,192)	(12,643)
Net Amount	$ 17,581	$ 24,768

v3.24.2.u1

Goodwill and Intangible Assets - Estimated Amortization Expense (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Oct. 01, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
2024 (remaining)	$ 11,322
2025	34,712
2026	23,334
2027	16,830
2028	16,320
Beyond	61,941
Net Amount	$ 164,459	$ 173,936

v3.24.2.u1

Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023	Oct. 01, 2023
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 176,790		$ 176,790		$ 177,477
Accumulated depreciation	(106,096)		(106,096)		(102,645)
Property and equipment, net	70,694		70,694		74,832
Depreciation expense related to property and equipment	5,700	$ 5,600	18,300	$ 13,700
Equipment, furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	130,748		130,748		132,744
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 46,042		$ 46,042		$ 44,733

v3.24.2.u1

Stock Repurchase and Dividends - Narrative (Details) - USD ($) $ in Millions	Jun. 30, 2024	Oct. 05, 2021
Subsequent Event [Line Items]
Remaining authorized amount under share repurchase program	$ 347.8
October 2021 Stock Repurchase Program
Subsequent Event [Line Items]
Maximum repurchase amount under stock repurchase program		$ 400.0

v3.24.2.u1

Stock Repurchase and Dividends - Schedule of Dividends Declared and Paid (Details) - USD ($) $ / shares in Units, $ in Thousands							3 Months Ended		9 Months Ended
	May 31, 2024	Feb. 27, 2024	Dec. 13, 2023	Jun. 06, 2023	Feb. 24, 2023	Dec. 09, 2022	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023
Stock Repurchase And Dividends [Abstract]
Dividend paid per share (in dollars per share)	$ 0.29	$ 0.26	$ 0.26	$ 0.26	$ 0.23	$ 0.23	$ 0.29	$ 0.26	$ 0.81	$ 0.72
Dividend Paid	$ 15,522	$ 13,908	$ 13,873	$ 13,840	$ 12,242	$ 12,186			$ 43,303	$ 38,268

v3.24.2.u1

Leases - Narrative (Details) $ in Millions	Jun. 30, 2024 USD ($)
Lessee, Lease, Description [Line Items]
Renewal term (up to)	5 years
Operating leases, not yet commenced	$ 13.9
Minimum
Lessee, Lease, Description [Line Items]
Remaining lease term	1 month
Maximum
Lessee, Lease, Description [Line Items]
Remaining lease term	10 years

v3.24.2.u1

Leases - Components of Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023
Leases [Abstract]
Operating lease cost	$ 24,562	$ 24,775	$ 73,580	$ 70,155
Sublease income	(184)	(46)	(347)	(125)
Total lease cost	$ 24,378	$ 24,729	$ 73,233	$ 70,030

v3.24.2.u1

Leases - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023
Leases [Abstract]
Operating cash flows for operating leases	$ 56,379	$ 57,871
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 38,160	$ 72,294

v3.24.2.u1

Leases - Supplemental Balance Sheet and Other Information (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Oct. 01, 2023
Operating leases:
Right-of-use assets	$ 167,317	$ 175,932
Lease liabilities:
Current	65,932	65,005
Non-current	128,892	144,685
Total operating lease liabilities	$ 194,824	$ 209,690
Weighted-average remaining lease term:
Operating leases	4 years	5 years
Weighted-average discount rate:
Operating leases	3.40%	3.00%

v3.24.2.u1

Leases - Maturity Analysis of the Future Undiscounted Cash Flows of Operating and Finance Lease Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Oct. 01, 2023
Operating Leases
2024 (remaining)	$ 20,124
2025	65,068
2026	44,638
2027	31,231
2028	20,176
Beyond	28,412
Total lease payments	209,649
Less: imputed interest	(14,825)
Total present value of lease liabilities	$ 194,824	$ 209,690

v3.24.2.u1

Employee Benefits (Details) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2024	Oct. 02, 2022
Retirement Benefits [Abstract]
Government assistance noncurrent liability		$ 21
Government assistance decrease in liability	$ 10
Government assistance current liability	$ 11

v3.24.2.u1

Stockholders' Equity and Stock Compensation Plans (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 8.1	$ 7.0	$ 23.7	$ 21.6
PSU's
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)			55,836
Fair value of awards granted (in dollars per share)			$ 203.53
Vesting period			3 years
Percentage of shares that ultimately vest depending on growth in diluted earnings per share			50.00%
Percentage of shares that ultimately vest depending on the shareholder return relative to peer group of companies over vesting period			50.00%
RSU's
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)			141,880
Fair value of awards granted (in dollars per share)			$ 164.78
RSU's | Executive officers and employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			4 years
RSU's | Non-employee director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			1 year

v3.24.2.u1

Earnings per Share ("EPS") (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023
Earnings Per Share [Abstract]
Net income attributable to Tetra Tech, basic	$ 85,810	$ 60,235	$ 237,228	$ 219,771
Net income attributable to Tetra Tech, diluted	$ 85,810	$ 60,235	$ 237,228	$ 219,771
Weighted-average common shares outstanding – basic (in shares)	53,515	53,231	53,451	53,188
Effect of dilutive stock options and unvested restricted stock (in shares)	433	422	415	427
Shares issuable assuming conversion of convertible notes (in shares)	104	0	35	0
Weighted-average common stock outstanding – diluted (in shares)	54,052	53,653	53,901	53,615
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 1.60	$ 1.13	$ 4.44	$ 4.13
Diluted (in dollars per share)	$ 1.59	$ 1.12	$ 4.40	$ 4.10

v3.24.2.u1

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Apr. 02, 2023	Jun. 30, 2024	Jul. 02, 2023	Oct. 01, 2023
Income Tax Disclosure [Abstract]
Effective tax rate		27.70%	28.30%
Reduction in income tax expense due to excess tax benefits on share-based payments		$ 2.9	$ 2.2
Income tax expense, nonoperating	$ 6.9	$ 4.3	$ 7.2
Effective tax rate, excluding excess tax benefits on share-based payments		27.20%	26.70%
Liability for uncertain tax positions		$ 64.0		$ 62.0

v3.24.2.u1

Reportable Segments - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024 USD ($)	Jul. 02, 2023 USD ($)	Jun. 30, 2024 USD ($) segment	Jul. 02, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			2
Acquisition and integration expenses	$ 0	$ 2,107	$ 0	$ 25,812
RPS Group PLC
Segment Reporting Information [Line Items]
Acquisition and integration expenses		$ 2,100		$ 25,800

v3.24.2.u1

Reportable Segments - Summary of Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023	Oct. 01, 2023
Segment Reporting Information [Line Items]
Revenue	$ 1,344,323	$ 1,208,947	$ 3,824,205	$ 3,261,938
Income from operations	128,630	97,675	357,395	250,736
Total Assets	4,084,905		4,084,905		$ 3,820,477
Operating segments | GSG
Segment Reporting Information [Line Items]
Revenue	640,553	531,050	1,812,721	1,565,371
Income from operations	71,518	54,496	198,652	167,053
Total Assets	632,346		632,346		543,066
Operating segments | CIG
Segment Reporting Information [Line Items]
Revenue	723,617	691,386	2,063,879	1,741,300
Income from operations	86,465	69,572	233,821	172,199
Total Assets	1,066,241		1,066,241		994,470
Elimination of inter-segment revenue
Segment Reporting Information [Line Items]
Revenue	(19,847)	(13,489)	(52,395)	(44,733)
Corporate
Segment Reporting Information [Line Items]
Income from operations	(29,353)	$ (26,393)	(75,078)	$ (88,516)
Total Assets	$ 2,386,318		$ 2,386,318		$ 2,282,941

v3.24.2.u1

Fair Value Measurements (Details) - USD ($)	Jun. 30, 2024	Oct. 01, 2023	Aug. 22, 2023
Debt Instrument [Line Items]
Long-term debt	$ 861,830,000	$ 879,529,000
Amended Revolving Credit Facility
Debt Instrument [Line Items]
Amount outstanding under credit facility	0
Amended Credit Agreement
Debt Instrument [Line Items]
Amount outstanding under credit facility	300,000,000
Amended Credit Agreement | New Term Loan Facility
Debt Instrument [Line Items]
Amount outstanding under credit facility	300,000,000
2028 Senior Notes | Convertible Debt
Debt Instrument [Line Items]
Principal amount	575,000,000		$ 575,000,000
Long-term debt	562,882,000	560,842,000
Convertible debt, estimated fair value	$ 674,000,000	$ 566,000,000

v3.24.2.u1

Long-Term Debt - Schedule of Long-Term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Oct. 01, 2023
Debt Instrument [Line Items]
Unamortized discount and issuance costs	$ (13,170)	$ (15,471)
Long-term debt	861,830	879,529
Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross	300,000	320,000
Convertible Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 575,000	$ 575,000

v3.24.2.u1

Long-Term Debt - Narrative (Details)	Jun. 30, 2024 USD ($) $ / shares	Aug. 22, 2023 USD ($) $ / shares	Feb. 18, 2022 USD ($)	Oct. 01, 2023 USD ($)	Aug. 17, 2023 $ / shares	Oct. 26, 2022 USD ($)
Line of Credit Facility [Line Items]
Derivative, cap price per share (in dollars per share) | $ / shares	$ 259.53	$ 259.56
Premium over reported sales price, percentage		0.65
Common stock, reported sales price (in dollars per share) | $ / shares					$ 157.31
Deferred tax liabilities	$ 17,254,000			$ 14,256,000
Bank overdrafts	0
Convertible Debt
Line of Credit Facility [Line Items]
Payments for capped calls		$ 51,800,000
Deferred tax liabilities				$ 12,900,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Repayments of long-term lines of credit		185,000,000
Amended Revolving Credit Facility
Line of Credit Facility [Line Items]
Amount outstanding under credit facility	0
Standby Letters of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount	50,600,000
2028 Senior Notes | Convertible Debt
Line of Credit Facility [Line Items]
Principal amount	$ 575,000,000	$ 575,000,000
Stated interest percentage		2.25%
Conversion ratio	0.0050862	0.0050855
Conversion price (in dollars per share) | $ / shares	$ 196.61	$ 196.64
Redemption price, percentage		100.00%
Threshold percentage of stock price trigger		130.00%
Proceeds from convertible debt		$ 560,500,000
Interest rate, effective percentage		2.79%
Term Loan Facility Due 2027
Line of Credit Facility [Line Items]
Repayments of secured debt		$ 234,400,000
Term Loan Facility Due 2026
Line of Credit Facility [Line Items]
Repayments of secured debt		$ 89,400,000
Amended Credit Agreement
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 750,000,000
Accordion feature, higher borrowing capacity option			$ 1,050,000,000.00			$ 1,550,000,000
Debt instrument term			5 years
Accordion feature, increase limit			$ 300,000,000
Amount outstanding under credit facility	$ 300,000,000
Weighted average interest rate, at point in time	6.72%
Debt covenant, maximum consolidated leverage ratio			3.25
Debt covenant, maximum consolidated leverage ratio			3.00
Ratio of indebtedness to net capital	1.51
Ratio of consolidated fixed charge coverage ratio	12.47
Amended Credit Agreement | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 500,000,000
Remaining borrowing capacity	$ 499,300,000
Amended Credit Agreement | Revolving Credit Facility | Base Rate | Secured Overnight Financing Rate (SOFR)
Line of Credit Facility [Line Items]
Basis spread on variable rate			1.00%
Amended Credit Agreement | Revolving Credit Facility | Base Rate | Fed Funds Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate			0.50%
Amended Credit Agreement | Revolving Credit Facility | Minimum | Secured Overnight Financing Rate (SOFR)
Line of Credit Facility [Line Items]
Basis spread on variable rate			1.00%
Amended Credit Agreement | Revolving Credit Facility | Minimum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate			0.00%
Amended Credit Agreement | Revolving Credit Facility | Maximum | Secured Overnight Financing Rate (SOFR)
Line of Credit Facility [Line Items]
Basis spread on variable rate			1.875%
Amended Credit Agreement | Revolving Credit Facility | Maximum | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate			0.875%
Amended Credit Agreement | New Term Loan Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity						$ 500,000,000
Amount outstanding under credit facility	300,000,000
Amended Credit Agreement | Term Loan Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 250,000,000
Amended Credit Agreement | Standby Letters of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity			100,000,000
Letters of credit outstanding, amount	700,000
Amended Credit Agreement | Swingline Loan
Line of Credit Facility [Line Items]
Maximum borrowing capacity			20,000,000
Amended Credit Agreement | Multicurrency Borrowings and Letters of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 300,000,000
Other Credit Facilities
Line of Credit Facility [Line Items]
Amount outstanding under credit facility	$ 0

v3.24.2.u1

Long-Term Debt - Net Carrying Amount of Senior Notes (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Oct. 01, 2023
Debt Instrument [Line Items]
Unamortized discount and issuance costs	$ (13,170)	$ (15,471)
Long-term debt	861,830	879,529
Convertible Debt
Debt Instrument [Line Items]
Principal	575,000	575,000
2028 Senior Notes | Convertible Debt
Debt Instrument [Line Items]
Principal	575,000	575,000
Unamortized discount and issuance costs	(12,118)	(14,158)
Long-term debt	$ 562,882	$ 560,842

v3.24.2.u1

Long-Term Debt - Schedule of Interest Expense (Details) - 2028 Senior Notes - Convertible Debt - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Jun. 30, 2024	Jun. 30, 2024
Debt Instrument [Line Items]
Interest expense	$ 3,234	$ 9,631
Amortization of discount and issuance costs	680	2,040
Total interest expense	$ 3,914	$ 11,671

v3.24.2.u1

Derivative Financial Instruments (Details) $ in Thousands, £ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Jun. 30, 2024 USD ($)	Jul. 02, 2023 USD ($)	Apr. 02, 2023 USD ($)	Jan. 01, 2023 USD ($)	Jun. 30, 2024 USD ($)	Jul. 02, 2023 USD ($)	Sep. 30, 2018 agreement	Jan. 23, 2023 USD ($)	Dec. 28, 2022 USD ($)	Dec. 28, 2022 GBP (£)	Oct. 02, 2022 USD ($)	Oct. 02, 2022 GBP (£)
Derivative [Line Items]
Gain on foreign currency forward contract	$ 0	$ 0			$ 0	$ 89,402
Loss on cash flow hedges recognized in comprehensive income	$ 0	$ 1,044			$ 0	$ 2,029
RPS Group PLC
Derivative [Line Items]
Derivative, forward exchange rate									1.086	1.086	1.0852	1.0852
Foreign Exchange Forward | RPS Group PLC
Derivative [Line Items]
Notional amount									$ 775,400	£ 714.0	$ 774,800	£ 714.0
Foreign currency forward contract, asset fair value								$ 109,300			$ 19,900
Gain on foreign currency forward contract			$ 21,400	$ 68,000
Interest Rate Swap | Designated as cash flow hedges | Derivatives designated as hedging instruments
Derivative [Line Items]
Number of derivative agreements | agreement							5

v3.24.2.u1

Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023
Reclassifications out of accumulated other comprehensive income (loss)
Beginning balance	$ 1,584,850	$ 1,355,668	$ 1,403,506	$ 1,183,137
Amounts reclassified from accumulated other comprehensive loss:
Other comprehensive income, net of tax	1,857	43,456	40,606	70,218
Ending balance	1,666,203	1,452,789	1,666,203	1,452,789
Accumulated Other Comprehensive Income (Loss)
Reclassifications out of accumulated other comprehensive income (loss)
Beginning balance	(156,546)	(181,381)	(195,295)	(208,144)
Other comprehensive income (loss) before reclassifications	1,857	42,362	40,606	67,808
Amounts reclassified from accumulated other comprehensive loss:
Interest rate contracts, net of tax		1,093		2,410
Other comprehensive income, net of tax	1,857	43,455	40,606	70,218
Ending balance	(154,689)	(137,926)	(154,689)	(137,926)
Foreign Currency Translation Adjustments
Reclassifications out of accumulated other comprehensive income (loss)
Beginning balance	(159,171)	(185,602)	(197,933)	(210,556)
Other comprehensive income (loss) before reclassifications	1,854	44,499	40,616	69,453
Amounts reclassified from accumulated other comprehensive loss:
Interest rate contracts, net of tax		0		0
Other comprehensive income, net of tax	1,854	44,499	40,616	69,453
Ending balance	(157,317)	(141,103)	(157,317)	(141,103)
Gain (Loss) on Derivative Instruments
Reclassifications out of accumulated other comprehensive income (loss)
Beginning balance	0	1,427	0	2,412
Other comprehensive income (loss) before reclassifications	0	(2,137)	0	(4,439)
Amounts reclassified from accumulated other comprehensive loss:
Interest rate contracts, net of tax		1,093		2,410
Other comprehensive income, net of tax	0	(1,044)	0	(2,029)
Ending balance	0	383	0	383
Net Pension Adjustments
Reclassifications out of accumulated other comprehensive income (loss)
Beginning balance	2,625	2,794	2,638	0
Other comprehensive income (loss) before reclassifications	3	0	(10)	2,794
Amounts reclassified from accumulated other comprehensive loss:
Interest rate contracts, net of tax		0		0
Other comprehensive income, net of tax	3	0	(10)	2,794
Ending balance	$ 2,628	$ 2,794	$ 2,628	$ 2,794

v3.24.2.u1

Commitments and Contingencies (Details)	Jul. 15, 2019 action
Commitments and Contingencies Disclosure [Abstract]
Number of qui tam actions	3

v3.24.2.u1

Related Party Transactions (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023	Oct. 01, 2023
Related Party Transaction [Line Items]
Revenue	$ 1,344,323	$ 1,208,947	$ 3,824,205	$ 3,261,938
Reimbursable costs	15,287	20,848	46,025	61,475
Accounts receivable, net	1,053,758		1,053,758		$ 974,535
Contract assets	118,556		118,556		113,939
Contract liabilities	(372,283)		(372,283)		(335,044)
Related Party
Related Party Transaction [Line Items]
Revenue	16,753	$ 22,373	50,157	$ 65,249
Accounts receivable, net	14,305		14,305		19,944
Contract assets	1,997		1,997		2,723
Contract liabilities	$ (3,708)		$ (3,708)		$ (3,158)

v3.24.2.u1

Subsequent Events - Narrative (Details)	Jul. 29, 2024 $ / shares	Sep. 05, 2024 shares
Common Stock | Forecast
Subsequent Event [Line Items]
Additional shares received (in shares) | shares		4
Subsequent Event
Subsequent Event [Line Items]
Quarterly cash dividend declared (in dollars per share) | $ / shares	$ 0.29
Conversion ratio	5

v3.24.2.u1

Subsequent Events - Schedule of Proforma (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023
Subsequent Event [Line Items]
Net income attributable to Tetra Tech, basic	$ 85,810	$ 60,235	$ 237,228	$ 219,771
Net income attributable to Tetra Tech, diluted	$ 85,810	$ 60,235	$ 237,228	$ 219,771
Weighted-average common shares outstanding – basic (in shares)	53,515	53,231	53,451	53,188
Effect of dilutive stock options and unvested restricted stock (in shares)	433	422	415	427
Shares issuable assuming conversion of convertible notes (in shares)	104	0	35	0
Diluted (in shares)	54,052	53,653	53,901	53,615
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 1.60	$ 1.13	$ 4.44	$ 4.13
Diluted (in dollars per share)	$ 1.59	$ 1.12	$ 4.40	$ 4.10
Pro Forma
Subsequent Event [Line Items]
Net income attributable to Tetra Tech, basic	$ 85,810	$ 60,235	$ 237,228	$ 219,771
Net income attributable to Tetra Tech, diluted	$ 85,810	$ 60,235	$ 237,228	$ 219,771
Weighted-average common shares outstanding – basic (in shares)	267,575	266,155	267,255	265,940
Effect of dilutive stock options and unvested restricted stock (in shares)	2,165	2,110	2,075	2,135
Shares issuable assuming conversion of convertible notes (in shares)	520	0	175	0
Diluted (in shares)	270,260	268,265	269,505	268,075
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 320	$ 230	$ 890	$ 830
Diluted (in dollars per share)	$ 320	$ 220	$ 880	$ 820

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