FERS Annuity Computation: How Your Federal Pension Is Calculated

The Basic Formula

The FERS basic annuity calculation looks straightforward on the surface:

Annual Pension = High-3 Average Salary × Years of Creditable Service × Multiplier

The multiplier is 1.0% for most retirees. It increases to 1.1% if you retire at age 62 or later with at least 20 years of creditable service. That distinction matters more than the 0.1% gap suggests — on a 30-year career with a $95,000 high-3, the 1.1% multiplier produces $31,350 per year versus $28,500 at 1.0%. That's $2,850 annually, compounding with COLAs for the rest of your life.

Calculating Your High-3 Average Salary

The high-3 is the highest average basic pay you earned during any three consecutive years of creditable service. For most employees approaching retirement, it's the final three years. OPM uses the rate of basic pay — your salary from the General Schedule (or equivalent pay system), locality pay, and any special rate supplements. Overtime, bonuses, awards, and allowances are excluded.

If you received a within-grade increase or promotion during those three years, OPM calculates the average using the exact dates each rate was in effect, not a simple three-year average of annual salaries.

Part-time complication. If you worked part-time during any period that falls within your high-3, OPM uses the full-time equivalent pay rate for that position — not your actual part-time earnings. So a GS-12 Step 5 working 20 hours per week has the same high-3 rate as a GS-12 Step 5 working 40 hours. The part-time impact shows up in the proration factor, not the salary figure.

Part-Time Proration

If your career included any part-time service, OPM applies a proration factor that scales down the annuity to reflect actual hours worked:

Proration Factor = Total Actual Hours Worked ÷ Total Full-Time Hours Available

The prorated formula becomes:

Annual Pension = High-3 × Service Years × Multiplier × Proration Factor

An employee with 25 years of service who worked full-time for 20 years and half-time for 5 years would have a proration factor of (20 × 2,087 + 5 × 1,044) ÷ (25 × 2,087) = 46,960 ÷ 52,175 = 0.90. The pension is 90% of what a continuous full-time employee would receive. Most online retirement calculators assume a proration factor of 1.0, which overstates the result for anyone with part-time service in their record.

Sick Leave Conversion

Unused sick leave at retirement converts to additional creditable service for the annuity computation — but not for eligibility. OPM uses a 2,087-hour work year, so 174 hours of sick leave equals roughly one additional month of service credit. The conversion adds fractional years to the service total in the annuity formula.

Important limitation: OPM only credits whole months in the final calculation. Any leftover days after combining your actual service with converted sick leave are dropped. Sick leave credit is also available under disability retirement under separate rules; deferred retirees forfeit their entire sick leave balance.

The MRA+10 Reduction

If you retire under the MRA+10 provision (reached your MRA with 10–29 years of service), a permanent age reduction applies: 5% for each full year under age 62, calculated monthly at five-twelfths of 1% per month. This is applied after the basic computation.

A worked example: a GS-13 Step 10 with a high-3 of $115,000, retiring at MRA of 57 with 18 years of service.

• Basic computation: $115,000 × 18 × 1.0% = $20,700
• Age reduction: 5 years under 62 = 25% reduction
• Reduced annuity: $20,700 × 0.75 = $15,525 per year

That 25% reduction is permanent — it doesn't go away at age 62. Postponing the annuity start until age 60 (if you have 20 years by then) or 62 eliminates the penalty entirely, though you forgo the pension payments during the postponement period.

Survivor Benefit Reduction

If you're married and elect the full survivor annuity (50% of your unreduced pension payable to your spouse after your death), your own annuity is reduced by 10%. A partial election (25% survivor annuity) costs a 5% reduction. These reductions are applied on top of any MRA+10 age reduction.

Electing less than the full survivor benefit requires your spouse's notarized consent on SF 3107-2. After your annuity begins, you can cancel or reduce the election within 30 days of your first regular payment, and you can add or increase a current-spouse election within 18 months; after those periods, the election is irrevocable.

Putting the Pieces Together

The order of operations matters. OPM computes your basic annuity using the high-3, service, multiplier, and proration factor. Then it applies any MRA+10 age reduction. Then the survivor benefit reduction. Each adjustment compounds on the previous one, so the final number can differ substantially from the basic formula result.

The FERS Retirement Eligibility & Timing Guide includes computation worksheets that walk through each step — including the part-time proration factor and sick leave conversion — so you can model your specific scenario before requesting your official estimate from HR.

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