Is My FERS Estimate Right? The 7 Errors That Skew Federal Retirement Numbers
Federal employees usually carry a number in their head — "I'll get about $2,800 a month." Ask where it came from and it's an old HR printout, a coworker's rule of thumb, or a generic online calculator. When we compare those numbers to properly computed projections, most are off, some badly. These are the seven usual suspects.
1. The high-3 isn't what you think it is
Your high-3 is the highest average basic pay over any 36 consecutive months — almost always your last three years, but not necessarily. It includes locality pay; it excludes overtime, bonuses, awards, and most premium pay (LEO availability pay is a notable exception). Two classic errors: using base pay without locality (understates), or using gross W-2 income with overtime (overstates — common for postal and VA workers).
2. Sick leave: counted, miscounted, or forgotten
Unused sick leave converts to extra computation service using OPM's 2,087-hour year — roughly 174 hours per month. 1,400 hours ≈ 8 months of extra service. Forgetting it understates the annuity; assuming it helps you reach eligibility overstates it (it never does). Leftover days that don't complete a full month are dropped, which occasionally makes working a couple more pay periods surprisingly valuable.
3. Missing the 1.1% bump — or assuming it wrongly
Retire at 62 or later with 20+ years and the multiplier is 1.1% instead of 1.0% — a 10% raise on the entire annuity. Estimates go wrong in both directions: people retiring at 61 years 11 months who model 1.1%, and people at 62/20 whose old printout still says 1%.
4. Survivor benefit reduction ignored
The default for married retirees is a full survivor annuity: 50% to your spouse, costing you a 10% reduction (25%/5% for the partial election). A $40,000 computed annuity becomes $36,000 in actual deposit. Estimates that show the unreduced figure aren't wrong about the formula — they're wrong about your paycheck.
5. FERS supplement math (or its earnings test)
The Special Retirement Supplement planning estimate uses your age-62 Social Security benefit × ((rounded civilian FERS years, capped at 40) ÷ 40) for eligible immediate unreduced retirements before 62, but not MRA+10. Two common errors are skipping the rounded-years proration and forgetting the earnings test: wages or self-employment income above the annual limit reduce the supplement by $1 for every $2 over.
6. Deposits, military time, and part-time service
Unpaid military deposit? Those years may not count. Temporary/non-deduction time? Depends on era and deposits. Part-time stretches prorate the annuity. Any of these can knock years off what you think is your service computation date — this is the #1 cause of "my official estimate came back lower than HR's earlier number."
7. Taxes and the FEHB premium reality
The gross annuity isn't take-home: federal tax on most of it, possible state tax, FEHB premiums (which in retirement lose the pre-tax treatment), survivor reduction, FEGLI. A $3,300 gross monthly annuity can land near $2,400 net. An estimate that stops at gross is a headline, not a plan.
The quick self-audit
Check your estimate against this list: right high-3 (with locality, without overtime)? Sick leave added to computation only? Correct multiplier for your age and service? Survivor reduction applied? Supplement based on rounded civilian FERS years divided by 40, with the earnings test considered? Service history verified deposit by deposit? Net after taxes and FEHB? Verify the result with your agency before filing.
Or let the calculator run the checklist for you. The FERS Report calculator applies all seven correctly in about two minutes, and the $29 report gives you the written breakdown to compare against HR's official estimate.
Educational content only — not financial, tax, or legal advice. OPM's official computation controls; verify your service history with your HR retirement specialist.