Earnings per Share ("EPS") (Tables)

3 Months Ended

Dec. 30, 2018

Earnings Per Share [Abstract]

Schedule of number of weighted-average shares used to compute basic and diluted EPS

The following table sets forth the number of weighted-average shares used to compute basic and diluted EPS:

	Three Months Ended
	December 30, 2018		December 31, 2017
	(in thousands, except per share data)
Net income attributable to Tetra Tech	$	41,997	$	46,034
Weighted-average common shares outstanding – basic	55,390		55,855
Effect of dilutive stock options and unvested restricted stock	976		1,020
Weighted-average common stock outstanding – diluted	56,366		56,875
Earnings per share attributable to Tetra Tech:
Basic	$	0.76	$	0.82
Diluted	$	0.75	$	0.81