5 CFR 831.701 - Effective dates of annuities.
(a) Except as provided in paragraphs (b) through (d) of this section, an annuity of an employee or Member commences on the first day of the month after -
(1) Separation from the service; or
(2) Pay ceases and the service and age requirements for title to annuity are met, if earlier than the date of separation.
(b) An annuity of -
(1) An employee involuntarily separated from service (except by removal for cause on charges of misconduct or delinquency) and eligible for an immediate annuity based on that involuntary separation;
(2) An employee or Member retiring due to a disability; and
(3) An employee or Member retiring after serving three days or less in the month of retirement - shall commence on the day after separation from the service or the day after pay ceases and the service and age or disability requirements for title to annuity are met.
(c) An annuity granted under section 8338, title 5, United States Code, commences on the appropriate birthday of the employee or Member.
(d) A phased retirement annuity and a composite retirement annuity granted to an employee under section 8336a of title 5, United States Code, and defined under § 831.1702, commences as provided in subpart Q of this part.
(e) Survivor annuities commence as provided in § 831.651.
(f) Except as provided in § 831.502, annuity terminates on the date of death or on the date of any other terminating event in each case when OPM terminates the annuity.
(g) Annuity accrues on a daily basis, one-thirtieth of the monthly rate constituting the daily rate. Annuity does not accrue for the thirty-first day of any month, except in the initial month if the employee's annuity commences on the 31st of a 31-day month. For accrual purposes, the last day of a 28-day month constitutes 3 days and the last day of a 29-day month constitutes 2 days.