Earnings per Share

3 Months Ended

Mar. 31, 2018

Basic and diluted earnings per share are calculated as follows:



	For the Three Months Ended March 31,
(In millions)	2018		2017
Numerator:
Net income attributable to Biogen Inc.	$	1,172.9	$	747.6
Denominator:
Weighted-average number of common shares outstanding	211.4		215.6
Effect of dilutive securities:
Stock options and employee stock purchase plan	—		—
Time-vested restricted stock units	0.2		0.2
Market stock units	0.1		0.1
Performance stock units settled in stock	—		—
Dilutive potential common shares	0.3		0.3
Shares used in calculating diluted earnings per share	211.7		215.9

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