Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Jan. 02, 2022	Dec. 27, 2020
Revenue	$ 858,510	$ 765,104
Gross profit	139,766	116,310
Selling, general and administrative expenses	(52,546)	(50,058)
Income from operations	87,220	66,252
Interest expense, net	(2,904)	(3,026)
Income before income tax expense	84,316	63,226
Income tax expense	(15,817)	(10,778)
Net income	68,499	52,448
Net income attributable to noncontrolling interests	(10)	(12)
Net income attributable to Tetra Tech	$ 68,489	$ 52,436
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 1.27	$ 0.97
Diluted (in dollars per share)	$ 1.25	$ 0.96
Weighted-average common shares outstanding:
Basic (in shares)	53,937	53,927
Diluted (in shares)	54,577	54,637
Subcontractor costs
Cost of revenue	$ (179,177)	$ (159,933)
Other costs of revenue
Cost of revenue	$ (539,567)	$ (488,861)