maximum of 8,000,000

Eligible employees may receive stock option awards annually with the number of shares and type of instrument generally determined by the employee’s salary grade and performance level. Incentive and stock option awards allow the recipient to purchase shares of our common stock at a set price, not to be less than the closing market price on the date of award, for no consideration payable by the recipient. The related number of shares underlying the stock option is fixed at the time of the grant. Options generally vest over a four-year period with a maximum term of five years from the vesting date. In addition, certain management and professional level employees may receive stock option awards upon the commencement of employment.

The fair value of each award is estimated as of the date of the grant using the Black-Scholes valuation model. The expected volatility reflects the consideration of the historical volatility of our common stock as determined by the closing price over a six to term commensurate with the expected term of the award. Expected dividends reflect the amount of quarterly distributions authorized and declared on our Class A and Class B common stock as of the grant date. The expected term of the awards is based on evaluations of historical and expected future employee exercise behavior. The risk-free interest rates for periods within the expected term of the award are based on the U.S. Treasury yield curve in effect during the period the options were granted. We have used historical data to estimate future forfeiture rates to apply against the gross amount of compensation expense determined using the valuation model. These estimates have approximated our actual forfeiture rates.

As of December 31, 2021, there was $0.1 million of total unrecognized compensation cost related to stock option awards. This cost is expected to be recognized over a weighted-average period of 2.2 years.