FERS High-3 Salary Calculation: What Counts and What Doesn't

The 36-Month Rule

The high-3 average salary is one of three inputs in the FERS pension formula, and it's the one most likely to contain errors that go undetected until OPM adjudicates your claim.

OPM defines the high-3 as the highest basic pay averaged over any 36 consecutive, completed months of federal service. For most employees, this is the final three years before retirement — but it doesn't have to be. If you took a voluntary downgrade, transferred to a lower-graded position, or had a period of reduced pay, an earlier 36-month window might produce a higher average.

The "consecutive" part matters. You can't cherry-pick your three highest-paid years if they aren't contiguous. And "completed months" means the window must cover 36 full months of service — the period can start on any day, not only the first of a calendar month.

What Counts as Basic Pay

This is where confusion starts. Basic pay for FERS retirement purposes is not the same as total compensation, gross pay, or even the number on your Leave and Earnings Statement's top line.

Included in your high-3:

• Base salary (your GS rate or equivalent)
• Locality pay adjustments
• Environmental differential pay
• Certain hazard pay differentials
• Availability pay (for criminal investigators under 5 U.S.C. § 5545a)
• Law enforcement officer premium pay (for FERS-covered positions)

Excluded from your high-3:

• Overtime pay
• Cash awards and performance bonuses
• Recruitment, relocation, and retention incentives
• Travel allowances and per diem
• Night differential and Sunday premium pay
• The lump-sum payout for unused annual leave at separation
• Credit hours (for employees on flexible schedules)

The practical test: basic pay is the exact amount from which FERS retirement deductions are withheld. Check your LES — the line showing your FERS contribution percentage (0.8% for standard FERS, 3.1% for FERS-RAE, or 4.4% for FERS-FRAE) is calculated against your basic pay. That base figure is what feeds the high-3.

Locality Pay and the High-3

Locality pay is included in the high-3 calculation, which creates a planning opportunity and a potential trap.

If you transfer from a high-locality area (Washington DC, San Francisco, New York) to a lower-locality area in your final years, your high-3 could actually be lower than if you'd stayed. Conversely, a transfer to a higher-locality area within your final three years would increase the average.

For employees in the Rest of United States (RUS) locality area who are considering a move to a higher-locality post, the timing matters. You'd need a full 36 consecutive months at the higher rate for it to fully replace your previous high-3 window. A move with only 18 months remaining before retirement would blend the two locality rates across the 36-month window.

The GS Biweekly Pay Cap

Federal employees whose combined base salary plus locality pay exceeds the biweekly pay cap face a complication. The official rate of basic pay for retirement is the payable rate — the amount from which FERS deductions are withheld. When a statutory cap clips locality pay, that capped payable rate is what belongs in the high-3, not a theoretical uncapped figure.

Here's where errors creep in. Some LES lines show gross pay or a pre-cap computation that does not match the official rate. This primarily affects senior GS-15 employees in high-locality areas and Senior Executive Service members.

To verify: compare the adjusted basic pay on your current SF-50 (Block 14) against the published GS pay table for your grade, step, and locality, and against the pay base used for your FERS deduction. If the SF-50 payable rate matches the deduction base, you're using the right number. If they diverge, resolve it with your payroll office before you file.

Part-Time High-3: The Full-Time Equivalent

If you've worked part-time during your federal career, the high-3 uses your full-time equivalent rate — not your actual reduced pay.

This is counterintuitive but intentional. OPM wants the high-3 to reflect the rate of pay you would have received at full-time. The part-time reduction is handled separately through the career-wide proration factor, which adjusts the final pension calculation.

So if you're a GS-13 working a 32-hour week at 80% schedule, your high-3 uses the full-time GS-13 salary rate for your locality. The 80% reduction gets applied later when OPM multiplies the pension amount by the proration factor.

This means switching from full-time to part-time in your final three years doesn't necessarily lower your high-3 — provided the rate of pay for the position hasn't changed. What it does lower is the proration factor, which reduces the final pension. But those are two different mechanisms.

Step Increases and Promotions Within the Window

Step increases and within-grade promotions during your final 36 months increase your high-3 proportionally. OPM averages all 36 months, so a step increase at month 30 raises the average by only 6/36 of the difference.

If you're expecting a promotion or step increase, the timing relative to your retirement date matters. A promotion that lands 35 months before separation gets averaged into nearly the entire 36-month window. One that lands 2 months before separation contributes to only 2/36 of the average.

This doesn't mean you should delay retirement to capture a step increase — the annuity difference is usually small compared to the additional month of full salary. But it's worth verifying that recent pay changes are reflected correctly in your SF-50 history before filing.

How to Verify Your High-3

Run your own calculation before trusting the agency estimate:

1. Pull your LES or SF-50 history for the most recent 36 consecutive months.
2. Extract the basic pay rate for each month (not gross pay, not take-home).
3. Sum all 36 months and divide by 36.
4. Compare this number to the high-3 on your agency's retirement estimate.

If they differ by more than a few dollars, one of three things happened: the agency used a different 36-month window, the payroll system recorded a capped rate instead of the authorized rate, or there's a data entry error in the personnel file.

Any discrepancy should be resolved with your HR office before filing SF-3107. Correcting the high-3 after your application reaches OPM adds months to an already lengthy adjudication process — average processing time is 108 days as of June 2026, and a returned file restarts the clock.

For a complete framework for auditing your high-3 alongside service computation dates, multiplier eligibility, and sick leave credit, the FERS Annuity Guide covers the verification workflow step by step.

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