Earnings Per Common Share

3 Months Ended

Mar. 31, 2021

Earnings Per Common Share [Abstract]

Earnings Per Common Share

Earnings Per Common Share

Basic earnings per common share (EPS) is computed by dividing net income attributable to Alexion by the weighted-average number of shares of common stock outstanding attributable to Alexion. For purposes of calculating diluted EPS, the denominator reflects the potential dilution that could occur if stock options, unvested restricted stock units or other contracts to issue common stock were exercised or converted into common stock, using the treasury stock method.

The following table summarizes the calculation of basic and diluted EPS for the three months ended March 31, 2021 and 2020:

	Three months ended
	March 31,
	2021		2020
Net income attributable to Alexion	$	636.0	$	557.6
Shares used in computing earnings per common share attributable to Alexion —basic	220.1		221.6
Weighted-average effect of dilutive securities:
Stock awards	2.5		1.0
Shares used in computing earnings per common share attributable to Alexion —diluted	222.6		222.6
Earnings per common share attributable to Alexion:
Basic	$	2.89	$	2.52
Diluted	$	2.86	$	2.50

We exclude from EPS the weighted-average number of securities whose effect is anti-dilutive. Excluded from the calculation of EPS for the three months ended March 31, 2021 and 2020 were 0.8 and 3.2 shares of Alexion common stock, respectively, because their effect is anti-dilutive.