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 closing of the IPO, all outstanding convertible preferred stock was converted into common stock (see Note 7). 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.

Basic and diluted net loss per share is computed by dividing net loss by the weighted-average number of that class 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:

	Year Ended December 31,
	2018		2017		2016
Series A convertible preferred stock		—		—		611,392
Series B convertible preferred stock		—		—		1,407,097
Unvested restricted common stock		26,841		57,629		100,634
Options to purchase common stock		3,014,984		2,043,420		1,063,778