Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2023	Jan. 01, 2023
Revenue	$ 1,228,267	$ 894,766
Gross profit	190,498	153,246
Selling, general and administrative expenses	(79,417)	(56,502)
Acquisition and integration expenses	0	(3,761)
Contingent consideration – fair value adjustments	0	(933)
Income from operations	111,081	92,050
Interest expense, net	(9,577)	(5,372)
Other non-operating income	0	67,995
Income before income tax expense	101,504	154,673
Income tax expense	(26,524)	(37,958)
Net income	74,980	116,715
Net income attributable to noncontrolling interests	(8)	(9)
Net income attributable to Tetra Tech, basic	74,972	116,706
Net income attributable to Tetra Tech, diluted	$ 74,972	$ 116,706
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 1.41	$ 2.20
Diluted (in dollars per share)	$ 1.40	$ 2.18
Weighted-average common shares outstanding:
Basic (in shares)	53,317	53,069
Diluted (in shares)	53,738	53,529
Subcontractor costs
Cost of revenue	$ (213,098)	$ (158,204)
Other costs of revenue
Cost of revenue	$ (824,671)	$ (583,316)