How the FERS pension calculation formula works

The basic formula

Federal Employees Retirement System (FERS) computes your basic annuity (the pension piece — separate from TSP and Social Security) with a single formula:

Annuity = High-3 × Years of Service × Multiplier

That's it. The complexity is in how each piece is defined.

High-3 average salary

Your High-3 is the average of your highest-paid 36 consecutive months of basic pay. "Basic pay" means base salary plus locality pay. It does NOT include bonuses, overtime, awards, or non-basic premium pay.

Most employees' High-3 ends up being their final three years because federal pay generally rises with grade promotions and step increases. But OPM looks at your entire history — if there was a higher-paid 36-month window earlier in your career, that one is used.

Years of creditable service

This includes all your civilian service under FERS, plus military service if you've made the deposit, plus unused sick leave (converted to months and days). Don't confuse "creditable service for computation" with "creditable service for eligibility" — sick leave counts for the former but not the latter.

The multiplier

The standard FERS multiplier is 1% per year of service.

If you meet BOTH conditions below at retirement, the multiplier becomes 1.1% per year:

1. You are at least age 62, AND
2. You have at least 20 years of creditable service.

The 1.1% multiplier is significant — it's a 10% boost to your annuity for life. Many federal employees with 19 years at age 62 deliberately stay one more year to cross the 20-year threshold.

A worked example

Consider a federal employee retiring at age 62 with 30 years of service and a High-3 of $100,000:

• High-3: $100,000
• Years of service: 30
• Multiplier: 1.1% (age 62, ≥20 years)
• Annuity: $100,000 × 30 × 0.011 = $33,000/year

If the same employee had retired at 61 instead, the multiplier would be 1.0% and the annuity would be $30,000/year — a $3,000/year difference for the rest of their life. Often the math justifies waiting that one extra year.

The FERS Supplement

If you retire before age 62 with full eligibility (e.g., MRA+30), you also receive the FERS Supplement, which approximates the Social Security you'd be earning if you were already 62. It stops the month you turn 62. The Supplement is computed roughly as: estimated SS at 62 × (years of FERS service ÷ 40).

Survivor benefits

You can elect a survivor annuity for your spouse. The standard election is 50% (which reduces your annuity by 10%) or 25% (which reduces it by 5%). Without election, your spouse loses health insurance eligibility under FEHB, which is usually a much bigger issue than the annuity itself.

Bottom line

FERS = High-3 × Years × Multiplier. Get to 20 years of service AND age 62 to unlock the 1.1% multiplier — it's the single highest-value retirement decision most federal employees make.