April 16, 2019 20:01 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 How can buying extra service credit give me a higher monthly defined benefit? What is service credit? Can I buy extra service credit in PERF? How I do I get my address corrected on the 1099-R form? How much will my 13th check be?