Capitol Police Retirement Reform Act of 2021 This bill revises the treatment of overtime pay for members of the U.S. Capitol Police for purposes of calculating certain annuity benefits, including benefits received upon a member's retirement. Specifically, the bill categorizes overtime pay as basic pay, subject to annual statutory maximums. (Basic pay is used to calculate a member's average earnings amount upon which benefits are based.) Overtime pay may only be treated as basic pay for purposes of a retirement annuity calculation under the Federal Employees Retirement System if the retiring member has completed at least 15 years of service. Further, such overtime pay may only be treated as basic pay if earned on or after the date of enactment, and only to the extent of the percentage allowable based upon the amount of service as set forth in this bill. However, 100% of all amounts received as overtime pay by members of the Capitol Police earned on or after the date of enactment are treated as basic pay for purposes of computing a disability annuity; and a survivor annuity, if based on the service of an individual who dies before separating from service.