8. Net Loss Per Share Attributable to Common Stockholders

The Company computed net loss attributable per common stockholder using the two-class method required for participating securities through the date of the IPO. Immediately prior to the IPO, all outstanding convertible preferred stock was converted into common stock (see Note 1). The Company considered convertible preferred stock to be participating securities. In the event that the Company had paid out distributions, holders of convertible preferred stock would have participated in the distribution.

The two-class method is an earnings (loss) allocation method under which earnings (loss) per share is calculated for common stock and participating security considering a participating security’s rights to undistributed earnings (loss) as if all such earnings (loss) had been distributed during the period. The convertible preferred stock did not have an obligation to fund losses and are therefore excluded from the calculation of basic net loss per share. The Company’s Series A and B convertible preferred stock were entitled to receive noncumulative dividends and in preference to any dividends on shares of the Company’s common stock.

Basic and diluted net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stock by the weighted-average number of common stock outstanding during the period. For periods in which the Company generated a net loss, the Company does not include the potential impact of dilutive securities in diluted net loss per share, as the impact of these items is anti-dilutive.

The following weighted-average equity instruments were excluded from the calculation of diluted net loss per share because their effect would have been anti-dilutive for the periods presented:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2017		2016		2017		2016
Series A convertible preferred stock		—		286,486		—		1,229,503
Series B convertible preferred stock		—		659,337		—		2,829,657
Unvested restricted common stock		63,431		106,055		68,693		111,345
Options to purchase common stock		1,894,831		1,031,128		1,618,721		843,975