Military Buyback Pension Calculation: How Much Will Your Annuity Increase?

The Annuity Formula Behind Military Buyback

The financial case for buying back military time comes down to one formula: how OPM calculates your FERS or CSRS annuity. Each year of credited military service directly increases the multiplier in that formula, which means a higher monthly pension check for every year of retirement.

Understanding the math is not optional — it is the only way to know whether the deposit cost is worth the lifetime return.

FERS Annuity Calculation With Military Service

The FERS basic annuity formula is:

High-3 Average Salary × Years of Creditable Service × Multiplier

The multiplier depends on your age and total service at retirement:

• 1.0% per year for most retirees
• 1.1% per year if you retire at age 62 or older with at least 20 years of total creditable service

That 0.1% difference sounds small, but it applies to every year of service — not just the military years. Reaching the 20-year threshold changes the multiplier for your entire career, not just the years above 20.

Here is what that looks like with real numbers. Take a federal employee with a high-3 average salary of $95,000:

Without military buyback (16 years civilian service, retiring at 62): $95,000 × 16 × 1.0% = $15,200/year

With military buyback (16 civilian + 4 military = 20 years, retiring at 62): $95,000 × 20 × 1.1% = $20,900/year

The difference is $5,700 per year — not just from the 4 extra years, but also from the multiplier bump from 1.0% to 1.1% across all 20 years. Over a 25-year retirement, that is $142,500 in additional annuity payments from a deposit that likely cost $4,000-$6,000 plus interest.

The High-3 Average Salary

Your high-3 is the highest average basic pay you earned during any 36 consecutive months of federal service. For most employees, this is the last three years before retirement, since federal pay generally increases through within-grade step increases and locality pay adjustments.

Military basic pay during your active-duty service does not factor into the high-3 calculation — only your civilian federal salary counts. The military years add to your total creditable service (the "years" variable in the formula), not to the salary component.

This means the annuity increase from military buyback scales with your civilian salary progression. The higher your GS grade and step at retirement, the more each bought-back military year is worth in annuity dollars.

CSRS Annuity Calculation With Military Service

CSRS uses a more generous multiplier structure:

• 1.5% per year for the first 5 years of service
• 1.75% per year for years 6-10
• 2.0% per year for all years beyond 10

For a CSRS employee with a high-3 of $95,000 who buys back 4 years of military service, the additional annuity from those 4 years depends on where they fall in the service brackets. If the employee already has 15 civilian years, the military years would all fall in the 2.0% bracket, adding $95,000 × 4 × 2.0% = $7,600 per year to the annuity.

Running Your Own Calculation

To estimate your annuity increase from military buyback:

1. Find your high-3. Check your most recent three years of earnings on your Leave and Earnings Statement. If you are not yet in your final three years, estimate based on your current salary and expected step increases.

2. Count your total creditable service with and without military years. Your Service Computation Date for retirement (SCD-Retirement) determines your current civilian service years. Add your active-duty military time to get the total with buyback.

3. Determine your multiplier. If you are FERS and will retire at 62+ with 20+ total years (including military), you get 1.1%. Otherwise, 1.0%. For CSRS, use the tiered brackets above.

4. Calculate both scenarios. The difference between the two annuity amounts is your annual return on the deposit investment.

One detail that trips people up: the years-of-service variable uses years and full months, not just whole years. Four years and seven months of military service credits as 4 years, 7 months — the fraction counts. OPM uses a 30-day-month convention (360-day year) for these calculations.

The 20-Year Threshold for FERS

The 1.1% multiplier at age 62 with 20 years of service is one of the most consequential thresholds in the FERS system. If your civilian service alone puts you at 17 or 18 years, buying back 3-4 years of military time could push you over the 20-year mark and unlock the higher multiplier for every year of your career.

Check your math carefully here. The difference between retiring with 19 years and 11 months versus 20 years and 0 months at age 62 is the difference between a 1.0% and 1.1% multiplier applied to your entire service history. For someone with a $95,000 high-3, that one-month difference changes the annuity from $18,905 to $20,900 — a $1,995 annual swing.

What About the FERS Supplement?

The FERS Special Retirement Supplement bridges the gap between your retirement date and age 62, approximating what your Social Security benefit would be for your FERS-covered service. Military buyback does not increase the FERS Supplement because the supplement is based only on your FERS-covered civilian earnings — years during which Social Security taxes were withheld from your federal pay.

Your military years increase your basic annuity, not the supplement. The supplement calculation is separate and uses only civilian FERS service.

Putting the Numbers in Context

The deposit cost for FERS is 3% of your military basic pay (plus interest if past the grace period). For CSRS, it is 7%. Most military buyback deposits for 4-6 years of active-duty service fall between $3,000 and $10,000 depending on rank, era of service, and accrued interest.

Compare that one-time cost to the annual annuity increase — then multiply by 20-30 years of expected retirement. The return on investment is typically 10:1 or higher for FERS employees, making military buyback one of the most financially efficient actions available to veteran federal employees.

The Military Buyback Guide for Federal Employees walks through the full annuity calculation with worksheets for both FERS and CSRS scenarios, including the interest calculation and break-even analysis.

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