This bill, titled the "Retirement Annuity Supplement Clarity Act," amends title 5, United States Code, to clarify the treatment of annuity supplement payments in court-ordered divisions of federal annuities. Specifically, it mandates that if a court decree divides a federal annuity, the associated annuity supplement payment shall be included in that division's computation. This inclusion is the default, unless the court order or agreement explicitly states that the annuity supplement should be excluded from the division. The legislation also includes important applicability provisions, particularly for past cases. It directs the Office of Personnel Management to make a one-time payment to certain "covered annuitants" who retired before the bill's enactment. These payments will compensate annuitants whose annuity supplements were retroactively recomputed between June 30, 2016, and the enactment date, leading to deductions from their annuities due to court-ordered divisions. Furthermore, the bill waives any overpayments made to covered annuitants or their former spouses that resulted from the prior exclusion of annuity supplements in court-ordered apportionments before this Act's enactment.