5 CFR 831.701 - Effective dates of annuities.
(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 -
(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.
(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.
(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.