The weighted average fair value of the stock option awards granted during the thirty-six week periods ended May 4, 2024 and May 6, 2023, using the Black-Scholes-Merton multiple-option pricing valuation model, was $915.03 and $764.68 per share, respectively, using the following weighted average key assumptions:
| | | | | |
| | Thirty-Six Weeks Ended | |
| | May 4, | | May 6, | |
| | 2024 | | 2023 | |
| | | | | |
Expected price volatility | | 29 | % | 29 | % |
Risk-free interest rate | | 4.8 | % | 3.8 | % |
Weighted average expected lives (in years) | | 5.4 | | 5.5 | |
Forfeiture rate | | 7 | % | 10 | % |
Dividend yield | | 0 | % | 0 | % |
During the thirty-six week period ended May 4, 2024, and the comparable prior year period, 185,304 and 208,482 stock options, respectively, were exercised at a weighted average exercise price of $801.74 and $705.52, respectively.
As of May 4, 2024, total unrecognized share-based expense related to stock options, net of estimated forfeitures, was approximately $131.2 million, before income taxes, which we expect to recognize over an estimated weighted average period of 3.1 years.
Restricted Stock Units:
Restricted stock unit awards are valued at the market price of a share of the Company’s stock on the date of grant. Grants of employee restricted stock units vest ratably on an annual basis over a four-year service period and are payable in shares of common stock on the vesting date. Compensation expense for grants of employee restricted stock units is recognized on a straight-line basis over the four-year service period, less estimated forfeitures, which are consistent with stock option forfeiture assumptions. Grants of non-employee director restricted stock units are made and expensed on January 1 of each year, as they vest immediately.
The Company made grants of 3,173 and 3,584 restricted stock unit awards at weighted average grant date fair values of $2,560.56 and $2,267.40, respectively, during the thirty-six week periods ended May 4, 2024 and May 6, 2023.
During the thirty-six week period ended May 4, 2024, and the comparable prior year period, 4,741 and 6,643 restricted stock unit awards, respectively, were vested at a weighted average grant date fair value of $1,617.00 and $1,276.32, respectively.
As of May 4, 2024, total unrecognized stock-based compensation expense related to nonvested restricted stock unit awards, net of estimated forfeitures, was approximately $8.5 million, before income taxes, which we expect to recognize over an estimated weighted average period of 2.6 years.
Total share-based compensation expense (a component of Operating, selling, general and administrative expenses) for the twelve and thirty-six week periods ended May 4, 2024, was $25.4 million and $71.3 million, respectively. For the comparable prior year periods, total share-based compensation expense was $20.0 million and $62.4 million, respectively.
For the twelve and thirty-six week periods ended May 4, 2024, 131,280 and 115,997, respectively, stock options were excluded from the diluted earnings per share computation because they would have been anti-dilutive. For the comparable prior year periods, 154,041 and 132,965 anti-dilutive stock options were excluded from the dilutive earnings per share computation.
See AutoZone’s Annual Report on Form 10-K for the year ended August 26, 2023 and other filings with the SEC for a discussion regarding the methodology used in developing AutoZone’s assumptions to determine the fair value of the