You cannot receive credit for any military service in your FERS retirement computation, if you are receiving military retired pay, unless you were awarded the retired pay:
However, you can elect to waive the retired pay and have the military service added to your civilian service in computing your FERS annuity. In addition to waiving your military retired pay you MUST pay a deposit for your post 1956 military deposit prior to separating from your agency in order for it to be creditable in your FERS retirement case.
If you want to waive your military retired pay to receive credit for military service in the computation of your FERS or CSRS benefit, you should write the Retired Pay Operations Center at least 60 days before your planned retirement. Send your waiver to:
Defense Finance and Accounting Service U.S. Military Retirement Pay P.O. Box 7130 London, KY 40742-7130
You can "fax" your request to 1 (800) 469-6559.
Suggested wording for your request is as follows:
"I (Full Name and Military Serial Number) hereby waive my military retired pay for Civil Service Retirement or Federal Employees Retirement System purposes effective (The day before your annuity begins). I hereby authorize the U.S. Office of Personnel management to withhold from my (CSRS or FERS) annuity any amount of military retired pay granted beyond the effective date of this waiver due to any delay in receiving or processing this request."