5 U.S.C. § 8464: Commencement and termination of annuities of employees and Members

separation from the service, in the case of an employee or Member retiring under section 8412, or subsection (a), (b)(1)(B), or (d) of section 8414; or pay ceases, and the applicable age and service requirements are met, in the case of an employee or Member retiring under section 8413; an annuity payable from the Fund commences on the day after separation from the service in the case of an employee retiring under subsection (b)(1)(A) or (c) of section 8414; and an annuity payable from the Fund commences on the day after separation from the service or the day after pay ceases and the requirements for title to an annuity are met in the case of an employee or Member retiring under section 8451. who retires under section 8412; and whose separation occurs upon the expiration of a term (or other period) for which the individual was appointed or elected. Except as otherwise provided in this chapter, the annuity of an annuitant under subchapter II or V of this chapter terminates on the date death or other terminating event occurs.