11.Stock-based compensation

Stock-based compensation expense is measured on the grant date based on the fair value of the award. Stock-based compensation expense is recognized on a straight-line basis over the requisite service period for awards expected to vest. The estimated grant date fair value of stock options was determined using a Black-Scholes valuation model using the following weighted-average assumptions for the periods indicated:

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The Company granted 61 and 248 stock options during the 13 weeks ended May 1, 2021 and May 2, 2020, respectively. Stock-based compensation expense for stock options was $2,897 and $2,475 for the 13 weeks ended May 1, 2021 and May 2, 2020, respectively. The weighted-average grant date fair value of these stock options was $109.72 and $54.40 for the 13 weeks ended May 1, 2021 and May 2, 2020, respectively. At May 1, 2021, there was approximately $20,470 of unrecognized stock-based compensation expense related to unvested stock options.

There were 52 and 152 restricted stock units issued during the 13 weeks ended May 1, 2021 and May 2, 2020, respectively. Stock-based compensation expense for restricted stock units was $4,835 and $4,187 for the 13 weeks ended May 1, 2021 and May 2, 2020, respectively. At May 1, 2021, there was approximately $36,761 of unrecognized stock-based compensation expense related to restricted stock units.

There were 46 performance-based restricted stock units issued during the 13 weeks ended May 1, 2021. There were no performance-based restricted stock units issued during the 13 weeks ended May 2, 2020. Stock-based compensation expense for performance-based restricted stock units was $1,246 for the 13 weeks ended May 1, 2021. Stock-based compensation benefit for performance-based restricted stock units was $480 for the 13 weeks ended May 2, 2020. At May 1, 2021, there was approximately $19,721 of unrecognized stock-based compensation expense related to performance-based restricted stock units.