Equity Plans

In June 2022, the Company’s board of directors adopted the Company’s 2022 Employment Inducement Equity Incentive Plan (the “Inducement Plan”). The Inducement Plan is a non-shareholder approved stock plan adopted pursuant to the “inducement exception” provided under Nasdaq listing rules. The Inducement Plan is used exclusively for the issuance of equity awards to certain new hires who satisfied the requirements to be granted inducement grants under Nasdaq rules as an inducement material to the individual’s entry into employment with the Company. The Company reserved 4,000,000 shares of common stock under the Inducement Plan and as of December 31, 2022, 3,587,950 shares remain available for issuance under the Inducement Plan.

In March 2018, the Company’s stockholders approved the Company's 2018 Equity Incentive Plan (as amended, the “2018 Plan”). On March 29, 2022, the Company’s stockholders approved an increase in the number of shares that may be issued under the 2018 Plan to 18.5 million. As of December 31, 2022, 3,900,900 shares remain available for issuance under the 2018 Plan.

In July 2017, the Company’s stockholders approved the Company's 2017 Equity Incentive Plan (the “2017 Plan”). A total of 4.7 million shares are authorized for issuance under the 2017 Plan. As of December 31, 2022, 767 shares remain available for issuance under the 2017 Plan. The 2017 Plan replaced the Company's 2008 Stock Incentive Plan (the “2008 Plan”), and no further awards will be made under the 2008 Plan.

Stock Options

Each option grants the holder the right to purchase from us one share of our common stock at a specified price, which is generally the closing price per share of our common stock on the date the option is issued. Options generally vest on a pro-rata basis on each anniversary of the issuance date within three years of the date the option is issued. Options may be exercised after they have vested and prior to the specified expiry date provided applicable exercise conditions are met, if any. The expiry date can be for periods of up to ten years from the date the option is issued. The fair value of each option is estimated on the date of grant using the Black-Scholes option pricing model based on the assumptions established at that time. The Company accounts for forfeitures as they occur and does not estimate forfeitures as of the option grant date.

The following table outlines the weighted average assumptions for options granted during the three months ended December 31, 2022 and 2021:

During the three months ended December 31, 2022 and 2021, the Company used historical volatility of our common stock over a period equal to the expected life of the options to estimate their fair value. The dividend yield assumption is based on the Company’s recent history and expectation of future dividend payouts on the common stock. The risk-free interest rate is based on the implied yield available on U.S. treasury zero-coupon issues with an equivalent remaining term.