Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 30, 2025	Mar. 31, 2024	Mar. 30, 2025	Mar. 31, 2024
Revenue	$ 1,322,113	$ 1,251,616	$ 2,742,674	$ 2,479,883
Gross profit	214,182	207,495	435,659	397,993
Selling, general and administrative expenses	(84,094)	(89,798)	(168,411)	(169,251)
Legal contingency costs	0	0	(115,000)	0
Contingent consideration – fair value adjustments	1,931	(14)	2,297	22
Goodwill impairment	(92,416)	0	(92,416)	0
Income from operations	39,603	117,683	62,129	228,764
Interest expense, net	(8,491)	(9,883)	(15,709)	(19,461)
Income before income tax expense	31,112	107,800	46,420	209,303
Income tax expense	(25,700)	(31,341)	(40,230)	(57,864)
Net income	5,412	76,459	6,190	151,439
Net income attributable to noncontrolling interests	(24)	(13)	(55)	(21)
Net income attributable to Tetra Tech	$ 5,388	$ 76,446	$ 6,135	$ 151,418
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 0.02	$ 0.29	$ 0.02	$ 0.57
Diluted (in dollars per share)	$ 0.02	$ 0.28	$ 0.02	$ 0.56
Weighted-average common shares outstanding:
Basic (in shares)	265,728	267,420	266,819	267,095
Diluted (in shares)	267,439	269,375	269,691	269,125
Subcontractor costs
Cost of revenue	$ (218,408)	$ (198,989)	$ (441,639)	$ (412,087)
Other costs of revenue
Cost of revenue	$ (889,523)	$ (845,132)	$ (1,865,376)	$ (1,669,803)