5 U.S.C. § 8333: Eligibility for annuity

An employee must complete at least 5 years of civilian service before he is eligible for an annuity under this subchapter. An employee or Member must complete, within the last 2 years before any separation from service, except a separation because of death or disability, at least 1 year of creditable civilian service during which he is subject to this subchapter before he or his survivors are eligible for annuity under this subchapter based on the separation. If an employee or Member, except an employee or Member separated from the service because of death or disability, fails to meet the service requirement of the preceding sentence, the amounts deducted from his pay during the service for which no eligibility for annuity is established based on the separation shall be returned to him on the separation. Failure to meet this service requirement does not deprive the individual or his survivors of annuity rights which attached on a previous separation. A Member or his survivor is eligible for an annuity under this subchapter only if the amounts named by section 8334 of this title have been deducted or deposited with respect to his last 5 years of civilian service, or, in the case of a survivor annuity under section 8341(d) or (e)(1) of this title, with respect to his total service.