Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Jan. 01, 2023	Jan. 02, 2022
Revenue	$ 894,766	$ 858,510
Gross profit	153,246	139,766
Selling, general and administrative expenses	(56,502)	(52,546)
Acquisition and integration expenses	(3,761)	0
Contingent consideration – fair value adjustments	(933)	0
Income from operations	92,050	87,220
Interest expense, net	(5,372)	(2,904)
Other Nonoperating Income (Expense)	67,995	0
Income before income tax expense	154,673	84,316
Income tax expense	(37,958)	(15,817)
Net income	116,715	68,499
Net income attributable to noncontrolling interests	(9)	(10)
Net income attributable to Tetra Tech, basic	116,706	68,489
Net income attributable to Tetra Tech, diluted	$ 116,706	$ 68,489
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 2.20	$ 1.27
Diluted (in dollars per share)	$ 2.18	$ 1.25
Weighted-average common shares outstanding:
Basic (in shares)	53,069	53,937
Diluted (in shares)	53,529	54,577
Subcontractor costs
Cost of revenue	$ (158,204)	$ (179,177)
Other costs of revenue
Cost of revenue	$ (583,316)	$ (539,567)