Earnings Per Common Share

6 Months Ended

Jun. 30, 2021

Basic earnings per common share is computed by dividing net income by the weighted average number of shares of common stock outstanding during the period. Diluted earnings per common share is computed by dividing net income by the weighted average number of shares of common stock outstanding during the period, adjusted for the potential dilutive effect of our outstanding stock options, restricted stock units, and shares issuable under the ESPP, as if they were vested and exercised.

The components of basic and diluted earnings per common share comprised the following (in millions, except per share amounts):


	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Numerator:
Net income	$	172.6	$	107.1	$	200.9	$	244.8
Denominator:
Weighted average outstanding shares — basic	44.8		44.1		44.7		44.0
Effect of dilutive securities(1):

Stock options, restricted stock units, and employee stock purchase plan	2.5		0.3		2.2		0.3
Weighted average shares — diluted(2)	47.3		44.4		46.9		44.3
Net income per common share:
Basic	$	3.85	$	2.43	$	4.49	$	5.56
Diluted	$	3.65	$	2.41	$	4.28	$	5.53

Stock options and restricted stock units excluded from calculation(2)	—		7.2		0.1		7.4

(1)Calculated using the treasury stock method.

(2)The common shares underlying certain stock options and restricted stock units have been excluded from the computation of diluted earnings per share because their impact would be anti-dilutive for the six-month period ended June 30, 2021 and for the three- and six-month periods ended June 30, 2020.