8. 2018 Stock Option and Grant Plan

In September 2018, the Company adopted the 2018 stock option and grant plan (the 2018 Plan), which provides for the Company to sell or issue common stock, or other stock-based awards, to employees, members of the board of directors and consultants of the Company. The 2018 Plan is administered by the board of directors, or at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or their committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than 10 years. The Company generally grants stock-based awards with service conditions only (service-based awards), although there has been one grant with performance conditions. Stock options granted under the 2018 Plan generally vest over three to four years. There were 2,580,453 shares reserved under the 2018 Plan for the future issuance of equity awards and, as of September 30, 2019, 638,042 shares were available for grant.

There were no awards in the nine months ended September 30, 2018. A summary of the stock option activity under the 2018 Plan is presented below:

The aggregate intrinsic value of options granted is calculated as the difference between the exercise price of the options and the estimated fair value of the Company’s common stock. The weighted average grant-date fair value of stock options granted during the nine months ended September 30, 2019 was $4.77. The aggregate grant-date fair value of options vested during the nine months ended September 30, 2019 was $276.

The Company uses the Black-Scholes option pricing method to calculate the grant-date fair value of an award. The fair values of options granted during the nine months ended September 30, 2019 were calculated using the following assumptions: risk-free interest rate of 1.39%—2.59% percent; expected term of 0.3—6.1 years; expected volatility of 70.3%—75.5% percent; and no expected dividend.

Stock-based Compensation

The Company recognizes stock-based compensation with respect to equity awards under the 2018 Plan and with respect to vesting common stock issued to founders. The Company has recorded stock-based compensation in the accompanying statements of operations as follows:

As of September 30, 2019, there was $5,650 of unrecognized compensation cost related to unvested option awards, including $527 with respect to one grant with performance-based vesting terms, which is expected to be recognized over a weighted-average period of 2.8 years. As of September 30, 2019, there was $1,088 of unrecognized compensation cost related to unvested stock awards granted to several Company founders, which is expected to be recognized over a weighted-average period of 1.6 years.