Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Apr. 02, 2023	Mar. 31, 2024	Apr. 02, 2023
Revenue	$ 1,251,616	$ 1,158,226	$ 2,479,883	$ 2,052,991
Gross profit	207,495	170,846	397,993	324,091
Selling, general and administrative expenses	(89,812)	(82,347)	(169,229)	(138,848)
Acquisition and integration expenses	0	(19,944)	0	(23,705)
Contingent consideration – fair value adjustments	0	(7,544)	0	(8,477)
Income from operations	117,683	61,011	228,764	153,061
Interest expense, net	(9,883)	(13,323)	(19,461)	(18,695)
Other non-operating income	0	21,407	0	89,402
Income before income tax expense	107,800	69,095	209,303	223,768
Income tax expense	(31,341)	(26,254)	(57,864)	(64,212)
Net income	76,459	42,841	151,439	159,556
Net income attributable to noncontrolling interests	(13)	(11)	(21)	(20)
Net income attributable to Tetra Tech, basic	76,446	42,830	151,418	159,536
Net income attributable to Tetra Tech, diluted	$ 76,446	$ 42,830	$ 151,418	$ 159,536
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 1.43	$ 0.80	$ 2.83	$ 3.00
Diluted (in dollars per share)	$ 1.42	$ 0.80	$ 2.81	$ 2.98
Weighted-average common shares outstanding:
Basic (in shares)	53,484	53,227	53,419	53,165
Diluted (in shares)	53,875	53,627	53,825	53,595
Subcontractor costs
Cost of revenue	$ (198,989)	$ (188,661)	$ (412,087)	$ (346,865)
Other costs of revenue
Cost of revenue	$ (845,132)	$ (798,719)	$ (1,669,803)	$ (1,382,035)