Basic net loss per share attributable to Portola Common Stockholders has been computed by dividing the net loss attributable to Portola Common Stockholders by the weighted-average number of shares of Common Stock outstanding during the period. Diluted net loss per share attributable to Portola Common Stockholders is calculated by dividing net loss attributable to Portola Common Stockholders by the weighted average number of shares of Common Stock and potential dilutive securities outstanding during the period. Since we were in a loss position for all periods presented, basic net loss per share attributable to Portola Common Stockholders is the same as diluted net loss per share attributable to Portola Common Stockholders as the inclusion of all potentially dilutive common shares would have been anti-dilutive.

The following outstanding shares of common stock equivalents were excluded from the computation of diluted net loss per share attributable to Portola Common Stockholders for the periods presented because including them would have been antidilutive:

	Six Months Ended June 30,
	2019		2018
Stock options to purchase common stock		7,913,656		7,391,411
Performance stock options		596,404		155,669
Common stock warrants		1,500		1,500
Restricted stock units		1,227,101		749,412
Performance stock units		13,125		330,416
Employee stock purchase plan		67,958		47,743

Up to 500,000 shares of our common stock may be contingently issued, if certain regulatory and performance conditions are met under an agreement with a contract manufacturer, as described in Note 6, “Contract Manufacturing Agreements”, to these condensed consolidated financial statements.