If you served in the military since 1956, you can credit that time toward your annuity but there are numerous complications and special rules.

For pure FERS employees, you can only receive civil service credit for post-1956 military service if you deposit an amount equal to a percentage of the military basic pay you earned while on active duty. In general, that deposit is 3 percent, plus interest. And you must complete the deposit before you retire if you want to get any credit for your military service.

On the other hand, if you are a CSRS employee, the deposit rules depend on when you were hired. If you were hired after September 30, 1982, you’ll be treated in the same way as a FERS employee. You will only get credit for your post-1956 military service if you make a deposit. However, CSRS employees must make a larger deposit – 7 percent plus interest.

On the other hand, if you were first employed under CSRS before October 1, 1982, it’s up to you whether to make a deposit. Either way, you’ll still get credit for your military service time. However, if you don’t make a deposit and are eligible for Social Security at age 62 (or later if you retire at or after age 62), those years of service will be eliminated and your annuity recomputed without them. That’s “Catch 62.”

So, if you expect to become eligible for Social Security benefits either at age 62 or at retirement, it may be worth making a deposit.

To find out what you owe, take your DD 214 or its equivalent and attach it to a copy of form RI 20-97, Estimated Earnings During Military Service (available at www.opm.gov/forms), and mail it to your branch of service. (The addresses are on the form.) The service center will verify your earnings.

If you don’t have a DD 214, you’ll have to fill out a SF-180, Request Pertaining to Military Records (available at www.archives.gov) and send it to the branch of service with which you served. (The addresses are on the form.) The records center will send you a new DD 214 or its equivalent. Attach that to a completed RI 20-97 and mail it to your branch of service to get an earnings estimate.

If you decide to make a deposit to cover your military service, you can take that paperwork to your personnel office and fill out a SF-2803, Application to Make Deposit or Redeposit (available at www.opm.gov/forms). You’ll make your deposits to your agency, not OPM. The sooner you make the deposit, the less interest you’ll have to pay.