Military Buyback Interest: How the Compounding Works and What You Owe

The Interest-Free Window

When you first enter a retirement-covered federal position, you get a grace period before interest starts accruing on any unpaid military service deposit. Under OPM rules, the grace period runs for two years from the date of your first civilian appointment under FERS or CSRS coverage. Interest begins accruing on the third anniversary of that date — the Interest Accrual Date (IAD).

In practical terms, if you started federal service on March 15, 2020, your IAD would be March 15, 2023. Any payment made before that date carries zero interest charges. After that date, the balance starts compounding.

How the Compounding Works

Military buyback interest is not a simple flat rate. It compounds annually on the IAD at variable rates set by the U.S. Treasury, based on the average yield of long-term government securities. Each year's rate applies to the full unpaid balance — your original base deposit plus all previously accumulated interest.

The formula: Total Owed = Base Deposit × (1 + r₁) × (1 + r₂) × ... × (1 + rₙ)

Where r₁ through rₙ are the Treasury rates for each year after your IAD.

Recent rates tell the story of how quickly this can add up:

• 2019: 2.750%
• 2020: 2.250%
• 2021: 1.375%
• 2022: 1.375%
• 2023: 1.875%
• 2024: 3.750%

A $3,000 base deposit from an IAD in 2010, left unpaid through 2024, would have accumulated over 14 years of compounding. The exact total depends on your specific IAD and the rates for each year, but balances commonly double or more over a 15- to 20-year career.

Why Free Online Calculators Get It Wrong

Most military buyback calculators online apply a single average interest rate across the entire period or use simplified annual compounding that doesn't account for the variable Treasury rate schedule. They also can't determine your actual IAD — that date depends on when you first entered retirement-covered federal employment, not when you enlisted or when you were discharged.

The only authoritative calculation comes from your agency HR benefits specialist, who uses the certified RI 20-97 (your verified military earnings) along with your specific IAD to compute the exact amount owed.

Stopping the Interest Clock

Interest stops accruing only when the deposit is paid in full. Making a partial payment does reduce the balance that future interest applies to, but it does not freeze interest on the remainder.

Your options for paying down the balance:

Biweekly payroll deductions reduce the principal steadily. Most agencies allow a minimum deduction of $25 per pay period, though higher amounts close the balance faster and reduce total interest.

Lump-sum payment through Pay.gov eliminates the balance immediately. Search for "DFAS Military Service Deposit Payment" or your agency's specific deposit tool on the Pay.gov portal.

Installment checks of $50 or more can be mailed directly to your payroll billing office.

The key timing insight: even if you can't pay the full amount today, starting payroll deductions immediately reduces the principal that next year's interest rate compounds against. Waiting another year means next year's Treasury rate applies to a larger balance.

The Real Cost of Waiting

Federal employees often delay the buyback because the upfront deposit feels like an expense they can push off. But the interest math makes waiting genuinely expensive. A $3,000 base deposit left unpaid for 20 years at historical Treasury rates could grow to $5,000 to $7,000 — and the pension increase from those bought-back years would have been accruing from day one of retirement had the deposit been completed earlier.

The Military Buyback Guide includes an interest calculation worksheet tied to the actual Treasury rate schedule, so you can estimate your current balance before your HR specialist runs the official numbers — and decide whether a lump sum or payroll deductions make more sense for your situation.

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