June 28, 2017 17:54 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 What is service credit? Can I buy extra service credit in the Teachers' Retirement Fund? How do I change the personal information INPRS has on file for me? How do I buy service credit? (1977 Fund) What does service credit have to do with my monthly pension benefit?