10.  Stock-Based Compensation

As of March 31, 2021, an aggregate of 4,709,277 shares of common stock were authorized under the Company’s 2019 Stock Incentive Plan (the “2019 Plan”), subject to an “evergreen” provision that will automatically increase the maximum number of shares of common stock that may be issued under the term of the 2019 Plan. As of March 31, 2021,  1,294,956 common shares were available for future grants under the 2019 Plan. As of March 31, 2021, 291,667 shares of common stock were authorized under the Company’s 2016 Consolidated Stock Incentive Plan (the “2016 Plan”) and 147,041 common shares were available for future grants under the 2016 Plan.

The Company recorded stock-based compensation expense in the following expense categories of its unaudited condensed consolidated statements of operations for the three and six months ended March 31, 2021 and 2020:

Stock Options

Below is a table summarizing the options issued and outstanding as of and for the six months ended March 31, 2021:

As of March 31, 2021, unrecognized compensation costs associated with the stock options of $4.8 million will be recognized over an estimated weighted-average amortization period of 1.3 years.

The weighted average grant date fair value of options granted during the six months ended March 31, 2021 and 2020 was $5.32 and $4.78, respectively.

Key assumptions used to estimate the fair value of the stock options granted during the six months ended March 31, 2021 and 2020 included:

During the six months ended March 31, 2021, the Company granted a stock option to purchase 225,000 shares to a consultant in recognition of future service to the Company as an employee. The exercisability and vesting of the stock options are subject to the consultant's effective date of employment with the Company, which has not yet occurred as of March 31, 2021, and as a result, the grant-date of such option has not occurred under GAAP. Therefore, the number and fair value of the shares subject to this option are not reflected in the table summarizing the options issued and outstanding as of and for the six months ended March 31, 2021 and did not have impact on unrecognized compensation costs or the estimated weighted-average amortization period above as of March 31, 2021.

Restricted Stock

A summary of the changes in the unvested restricted stock during the six months ended March 31, 2021 is as follows: