13. Net Loss per 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 shares of common stock outstanding for the period. Prior to the Company’s IPO in July 2015, the Company’s convertible preferred stock was entitled to receive dividends, prior and in preference to any declaration or payment of any dividend on common stock and thereafter participate pro rata on an as converted basis with the common stock holders on any distributions to common stockholders. The convertible preferred shares were therefore considered to be participating securities. As a result, the Company calculated the net loss per share using the two-class method. Accordingly, the net loss attributable to common stockholders is derived from the net loss for the period and, in periods in which the Company has net income attributable to common stockholders, an adjustment is made for the noncumulative dividends and allocations of earnings to participating securities based on their outstanding shareholder rights. Under the two-class method, the net loss attributable to common stockholders is not allocated to the convertible preferred stock as the convertible preferred stock did not have a contractual obligation to share in the Company’s losses.

In periods when the Company has incurred a net loss, common stock equivalents such as outstanding common stock options, restricted stock units, unvested common shares subject to repurchase and warrants are excluded from the calculation of diluted net loss per share as they give an anti-dilutive effect.

For the year ended December 31, 2017, the Company reversed $1.1 million of remeasurement gain on the change in the fair value of warrants from its net loss and included the incremental shares from the assumed exercise of the warrants in the computation of its weighted-average shares outstanding as they yielded a dilutive effect to the net loss per share in the period. Other potentially dilutive common stock equivalents such as outstanding common stock options, shares to be purchased under the employee stock purchase plan, and restricted stock units were excluded as their effect was anti-dilutive and the net loss per share would be reduced.

The following table provides the basic and diluted net loss per share computations for the years ended December 31, 2017, 2016 and 2015.


	Year ended December 31,
(in thousands, except per share data)	2017		2016		2015

Numerator:
Net loss used to compute net loss per share, basic	$	(136,314)	$	(95,765)	$	(70,275)

Less: Remeasurement gain on warrant liability		(1,148)		—		—
Net loss used to compute net loss per share, diluted	$	(137,462)	$	(95,765)	$	(70,275)

Denominator:
Weighted-average common shares outstanding		53,312		51,667		27,687
Less: Weighted-average unvested common shares subject to repurchase		—		(91)		(1,483)
Weighted-average number of shares used in computing net loss per share, basic		53,312		51,576		26,204

Add: Incremental shares from assumed exercise of warrants		292		—		—
Weighted-average number of shares used in computing net loss per share, diluted		53,604		51,576		26,204

Net loss per share, basic	$	(2.56)	$	(1.86)	$	(2.68)
Net loss per share, diluted	$	(2.56)	$	(1.86)	$	(2.68)

The following table shows the potentially dilutive common stock equivalents that were excluded from the computations of diluted net loss per share as their effect would be anti-dilutive, as of December 31, 2017, 2016 and 2015:


	As of December 31,
	2017	2016	2015

Options to purchase common stock	9,963	9,043	9,316
Warrants to purchase common stock	—	377	377
Restricted stock units	389	159	—
Employee stock purchase plan	79	90	—
Common stock subject to repurchase	—	—	1,307
	10,431	9,669	11,000