Optional service credit is any service credit you have the option to claim or purchase. In all cases, your service must be verified by TRS, and your request for the service credit must be made before your effective retirement date. Creditable service includes the following:
Prior Service: Any creditable service you rendered with a New York City and/or New York State public employer before joining TRS that was not transferred to TRS with your membership. (For Tier I members, service rendered outside of New York City is not creditable as prior service. See Outside Teaching Service below.)
Amman Service: Creditable service, such as substitute teaching or per diem service, that you rendered with a New York City or New York State public employer during a leave of absence from your TRS-eligible position or after separating from service. (For Tier I members, service rendered outside of New York City is not creditable as Amman service.)
Military Service: Eligible military service that interrupted your employment prior to or after becoming a TRS member.
Outside Teaching Service (Tier I only): Creditable teaching and/or pedagogical supervisory service rendered on a regular per-annum basis in a school or college not maintained by the City of New York.
Leaves of Absence Without Pay: Periods that may be creditable under limited circumstances.