May 14, 2018 21:31 Updated Follow There are several things that factor into the final cost of extra service. We suggest you read Buying Extra Service Credit if you are a member of PERF or TRF. For other funds, . Related articles Can I buy extra service credit in PERF? How do I buy service credit? (1977 Fund) I was in the military. How can I add this service to my account? When will I be vested in PERF? What is service credit?