Stock Purchase Warrants

6 Months Ended

Jun. 30, 2019

Warrants and Rights Note Disclosure [Abstract]

The Company has historically issued warrants to purchase shares of the Company’s common stock in connection with certain of its common stock offerings and in December 2017 the Company issued warrants in connection with a previous loan agreement. The following table describes the outstanding warrants classified in equity as of June 30, 2019:



		December 2017 Warrants
Exercise price		$4.27
Expiration date		December 6, 2023
Total shares issuable on exercise		26,951

The fair value of the warrants described in the table above were initially measured using the Black-Scholes valuation model. Inherent in the Black-Scholes valuation model are assumptions related to expected stock-price volatility, expected life, risk-free interest rate and dividend yield. The Company estimates the volatility of its common stock-based on historical volatility that matches the expected remaining life of the warrants. The risk-free interest rate is based on the U.S. Treasury zero-coupon yield curve on the grant date for a maturity similar to the expected remaining life of the warrants. The expected life of the warrants is assumed to be equivalent to their remaining contractual term. The dividend rate is based on the historical rate, which the Company anticipates remaining at zero.