Earnings per Share

6 Months Ended

Jun. 30, 2020

Earnings Per Share [Abstract]

Earnings per Share

Basic and diluted earnings per share are calculated as follows:

	For the Three Months Ended June 30,				For the Six Months Ended June 30,
(In millions)	2020		2019		2020		2019
Numerator:
Net income attributable to Biogen Inc.	$	1,542.1	$	1,494.1	$	2,941.2	$	2,902.9
Denominator:
Weighted average number of common shares outstanding	160.6		190.3		166.7		193.4
Effect of dilutive securities:
Time-vested restricted stock units	0.1		0.1		0.1		0.2
Market stock units	0.1		—		0.1		0.1
Performance stock units settled in stock	0.1		—		0.1		—
Dilutive potential common shares	0.3		0.1		0.3		0.3
Shares used in calculating diluted earnings per share	160.9		190.4		167.0		193.7

Amounts excluded from the calculation of net income per diluted share because their effects were anti-dilutive were insignificant.