Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 27, 2021	Jun. 28, 2020	Jun. 27, 2021	Jun. 28, 2020
Revenue	$ 801,633	$ 709,771	$ 2,321,500	$ 2,241,527
Gross profit	125,696	114,397	354,490	321,134
Selling, general and administrative expenses	(55,859)	(50,822)	(157,788)	(148,299)
Contingent consideration – fair value adjustments	(30)	(50)	163	1,521
Income from operations	69,807	63,525	196,865	174,356
Interest expense	(2,737)	(3,564)	(8,585)	(10,412)
Income before income tax expense	67,070	59,961	188,280	163,944
Income tax expense	(15,146)	(14,458)	(38,380)	(34,710)
Net income	51,924	45,503	149,900	129,234
Net income attributable to noncontrolling interests	(21)	(6)	(44)	(29)
Net income attributable to Tetra Tech	$ 51,903	$ 45,497	$ 149,856	$ 129,205
Earnings per share attributable to Tetra Tech:
Basic (in dollars per share)	$ 0.96	$ 0.84	$ 2.77	$ 2.38
Diluted (in dollars per share)	$ 0.95	$ 0.83	$ 2.74	$ 2.34
Weighted-average common shares outstanding:
Basic (in shares)	54,117	53,985	54,095	54,366
Diluted (in shares)	54,666	54,692	54,698	55,161
Subcontractor costs
Cost of revenue	$ (163,590)	$ (149,494)	$ (478,461)	$ (482,768)
Other costs of revenue
Cost of revenue	$ (512,347)	$ (445,880)	$ (1,488,549)	$ (1,437,625)