How to Fill Out SF 3108: Application to Make Service Credit Payment

To fill out SF 3108, the Application to Make Service Credit Payment, you complete Part A with your personal information and a chronological list of every period of federal civilian service you’ve performed, then hand the form to your agency’s HR office so they can verify your record in Part B and forward it to the Office of Personnel Management (OPM). If you’ve already left federal service, you skip the agency step and mail the form to OPM yourself. No payment goes with the form; OPM calculates what you owe and bills you afterward.¹

Before You Start

Pull your records first. You’ll need exact start and end dates for every period of federal civilian service, the agency name for each, and whether retirement deductions were withheld from your pay during that time. Your SF-50 (Notification of Personnel Action) forms and old pay stubs are the best sources. Mismatched or approximate dates are one of the most common reasons applications stall in processing.

Confirm the service you want to buy back is actually eligible. Two groups can file: current FERS-covered employees, and former FERS employees who left federal service with at least five years of paid creditable civilian service (which gives you a vested right to a deferred annuity).¹

One boundary matters before you file. With narrow exceptions, FERS employees cannot make a deposit for non-contributory civilian service performed after January 1, 1989.² If the service you want to purchase is uncovered civilian time entirely after that date, this form won’t get you credit for it. Pre-1989 civilian service and refunded FERS deductions from any period are both eligible. Peace Corps and VISTA volunteer service is also creditable regardless of when it was performed, with training periods excluded.³

Completing Part A

The form is a fillable PDF on OPM’s website.¹ Part A is everything you fill in yourself. Work through it block by block.

Items 1 through 4 ask for your full legal name, any other names you’ve used (maiden name, prior married name), your date of birth, and current mailing address.

Items 5 through 8 cover your employment identity: the department or agency where you currently work or last worked, including the bureau or division; your duty location (city and state); your Social Security number; and your position title.

Item 9 asks whether you’ve previously filed any retirement application under FERS or the Civil Service Retirement System (CSRS). If you have, include the claim number.

Item 10 is where you indicate the type of service credit payment you’re requesting: civilian service, military service, or both.

Items 11 and 12 ask whether FERS deductions are currently being withheld from your pay, and if not, the date you separated from your last FERS-covered position.

Items 13 through 16 close out with your signature, daytime phone number, email address, and the date you signed.

The Service History Table

Below the personal-information fields is a table where you list every period of federal civilian service in chronological order. For each period, provide the agency name, exact start and end dates, and check the box showing whether retirement deductions were not withheld, were withheld and refunded to you, or were withheld and remain on account.¹

List all of your federal service, not just the periods you want to buy back. OPM needs the complete picture to bill you the correct amount. The deduction-status box you check determines whether the period is treated as a deposit (never withheld) or a redeposit (withheld and refunded), and those two categories carry different consequences if left unpaid.

Part B: What Your Agency Fills In

If you’re a current federal employee, hand the completed Part A to your human resources or payroll office. They fill in Part B by pulling your official personnel records and verifying every period of federal civilian service you’ve performed, along with the retirement system that covered each period (FERS, CSRS, CSRS-Offset, or FICA only).¹

Part B also has a section where the agency documents the basic salary you actually earned during any civilian service that was not covered by FERS or CSRS. This salary data feeds directly into OPM’s deposit calculation. Once the agency representative signs and certifies the information, they forward the entire package to OPM.

Former employees who are no longer on a federal payroll skip Part B entirely. There’s no agency to verify your records, so you deal with OPM directly.

Where to Send the Form

Your submission route depends on your current status.

Current employees: Give the completed Part A to your agency’s HR or payroll office. They handle Part B and forward the package to OPM on your behalf.

Former employees: Mail the form directly to the Office of Personnel Management, Federal Employees Retirement System, P.O. Box 200, Boyers, PA 16020.¹

Do not include any payment with your submission. No money changes hands at this stage.

A Note on Military Service

SF 3108 can start the process of buying back military service performed after December 31, 1956, but the actual military deposit application is a companion form called SF 3108A, and only current FERS-covered employees can apply for military deposits.¹ Separated employees are not eligible for the military piece. If military service is your goal, expect to also complete Form RI 20-97 (Estimated Earnings During Military Service) and send it to the Defense Finance and Accounting Service, with your DD-214 or an equivalent document attached.⁴

What Happens After You Submit

OPM reviews the application, verifies the service, and calculates what you owe. Processing typically takes several weeks to a few months, depending on OPM’s workload and whether your records need additional verification.

For civilian service deposits, the base amount is 1.3 percent of the basic pay you earned during each period of uncovered service, regardless of what the deduction rate would have been at the time. Interest accrues on top of that. OPM uses variable interest rates that change each calendar year; for 2026 the rate is 4.25 percent, down from 4.375 percent in 2025. Interest compounds annually and continues to accrue until the deposit is paid in full or your annuity begins, whichever comes first.³

Once OPM finishes the calculation, they mail you a detailed billing statement showing the total owed, including principal and accumulated interest. The statement includes a Service Credit claim number you’ll need for all future payments. Hold onto it.

Paying the Bill

After you receive the statement and claim number, you have three ways to pay.

Pay.gov. OPM hosts a dedicated “Service Credit for Active Employees” portal on Pay.gov. You’ll need your Service Credit claim number and CSD number. The site accepts bank account (ACH) transfers and debit or credit cards. The minimum electronic payment is $25, except for a final annual payment.⁵

Check or money order by mail. Send it to OPM’s Retirement Operations Center at P.O. Box 45, Boyers, PA 16017. Write your claim number on the check.⁶

Installments. You don’t have to pay the full amount at once. OPM accepts installment payments, though paying faster reduces the interest that keeps accruing on the remaining balance.

Once the deposit is paid in full, OPM adds the service time to your retirement record.

Timing Matters More Than a Deadline

There is no hard deadline to submit SF 3108 while you’re still employed. But interest compounds every year you delay, and the deposit must be fully paid by the time your annuity begins. Any balance remaining when you retire can’t be paid afterward for deposit-type service.

The consequences of leaving it unpaid depend on which category your service falls into. For deposit service where deductions were never withheld, unpaid time simply doesn’t count toward your eligibility to retire or your annuity calculation. For redeposit service where you took a refund of contributions, the time still counts toward eligibility, but your annuity and any survivor benefit are permanently reduced.³ Filing early keeps the interest clock as short as possible and gives you room to spread payments out.

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U.S. Office of Personnel Management. SF 3108 – Application to Make Service Credit Payment
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U.S. Office of Personnel Management. Creditable Service
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U.S. Office of Personnel Management. Service Credit
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United States Office of Personnel Management. SF 3108 Application to Make Service Credit Payment
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Pay.gov. OPM Service Credit for Active Employees
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U.S. Office of Personnel Management. Contact OPM Retirement Services