Earnings per Share

12 Months Ended

Dec. 31, 2019

Earnings Per Share [Abstract]

Earnings per Share

Earnings per Share

Basic and diluted earnings per share are calculated as follows:

	For the Years Ended December 31,
(In millions)	2019		2018		2017
Numerator:
Net income attributable to Biogen Inc.	$	5,888.5	$	4,430.7	$	2,539.1
Denominator:
Weighted average number of common shares outstanding	187.1		204.9		212.6
Effect of dilutive securities:
Stock options and employee stock purchase plan	—		—		0.1
Time-vested restricted stock units	0.2		0.3		0.2
Market stock units	0.1		0.1		0.1
Performance stock units settled in stock	—		—		—
Dilutive potential common shares	0.3		0.4		0.4
Shares used in calculating diluted earnings per share	187.4		205.3		213.0

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

Earnings per share for the years ended December 31, 2019, 2018 and 2017, reflects, on a weighted average basis, the repurchase of approximately 23.6 million shares, 14.8 million shares and 3.7 million shares of our common stock, respectively, under our March 2019, 2018 and 2016 Share Repurchase Programs.