Net Loss Per Common Share

Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is computed using the weighted average number of common shares outstanding and, when dilutive, potential common share equivalents from outstanding options and unvested RSUs settleable in shares of common stock (using the treasury-stock method), and potential common shares from convertible securities (using the if-converted method). Because the Company reported a net loss for the twelve months ended months ended December 31, 2017 and the twelve months ended months ended December 31, 2016, all potential dilutive common shares have been excluded from the computation of the diluted net loss per share for all periods presented, as the effect would have been anti-dilutive.

Outstanding anti-dilutive securities not included in diluted net loss per share attributable to common stockholders calculation (in millions):



	Years Ended December 31,
	2017	2016	2015
Options outstanding to purchase common stock	0.4	0.7	1.3
Unvested restricted stock units	2.7	3.7	4.1
Senior convertible notes	4.0	—	—
Total	7.1	4.4	5.4