Federal Employee Retirement (FERS) Calculator
Calculate FERS basic benefit annuity, FERS Supplement, and TSP projection based on years of service and High-3 average salary. Projects total retirement income from FERS pension, Social Security, and TSP withdrawals with 2026 contribution limits.
2026 limit: $24,500/year ($2,041/month)
4% rule is common
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Introduction
Federal employees under FERS routinely underestimate their retirement income by 20% to 35% because they calculate only the FERS basic annuity and ignore the Thrift Savings Plan balance and Social Security component that together form the three-legged retirement system. According to the Office of Personnel Management, a federal employee with 30 years of service who retires at their Minimum Retirement Age receives a FERS basic annuity of just 30% of their High-3 average salary — far below the 70% to 80% income replacement ratio financial planners typically recommend. The remaining income must come from TSP withdrawals and Social Security benefits. Missing any one component, or miscalculating the High-3 average, produces retirement projections that are off by $10,000 to $25,000 per year in total income. This calculator computes all three FERS components simultaneously so federal employees can see their complete retirement picture and determine whether they are on track.
What This Calculator Does
This calculator computes the three components of FERS retirement income: the FERS basic annuity (percentage of High-3 salary times years of service), projected TSP balance at retirement (based on current balance, contribution rate, and years to retirement), and estimated Social Security benefit based on years of covered earnings. It also calculates the FERS Special Retirement Supplement (SRS) for employees who retire before Social Security eligibility age. Inputs include current salary, High-3 average, years of federal service, MRA, TSP balance, contribution rate, and estimated Social Security benefit from your SSA statement.
The Formula
The FERS basic annuity multiplies the High-3 average (the average of the highest 36 consecutive months of salary) by 1% per year of service. Employees who retire at age 62 or older with 20+ years receive a 1.1% multiplier instead. The Special Retirement Supplement approximates the Social Security portion earned during federal service, payable from retirement to age 62 (or until other earned income exceeds $22,320 in 2026). TSP balance projects using compound growth on current balance plus future contributions at the assumed annual return rate. The three income streams combined determine total gross retirement income.
Step-by-Step Example
Calculate the FERS basic annuity
High-3 average salary: $85,000. Years of service: 28 years. Age at retirement: 58 (below 62, so 1% multiplier applies). Annuity: $85,000 × 1% × 28 = $23,800/year ($1,983/month before FEHB premium deduction).
Project TSP balance at retirement
Current TSP balance: $280,000. Years to retirement: 7. Annual contribution: $23,000 (including agency match, 2026 limit is $23,500 employee + 5% agency match). Assumed 6% annual return. Projected balance: approximately $540,000 using the compound growth formula.
Estimate the FERS Special Retirement Supplement
Estimated Social Security benefit at 62 (from SSA statement): $1,840/month. FERS service years: 28. Total SS eligible years (assumed): 35. SRS = $1,840 × (28/35) = $1,472/month. Payable from age 58 to 62, then replaced by actual Social Security benefit.
Total retirement income picture
Age 58 income: Annuity $1,983 + SRS $1,472 = $3,455/month + TSP withdrawals (4% of $540,000 = $1,800/month) = $5,255/month gross. At age 62: Annuity $1,983 + Social Security $1,840 + TSP $1,800 = $5,623/month. Compare to pre-retirement income: $85,000 ÷ 12 = $7,083/month. Replacement rate: 74% to 79% depending on age.
Real-World Use Cases
MRA+10 Retirement Decision Analysis
A GS-12 employee at age 55 with 15 years of service is considering MRA+10 retirement (retirement at MRA with 10 to 29 years of service). The calculator shows their annuity would be reduced by 5% per year under age 62 — a 35% penalty for retiring 7 years early — producing an annuity of $6,890/year rather than the $10,600 they would get at 62. The employee decides to continue working to avoid the reduction.
Buyback of Non-Covered Service Impact
A federal employee has 4 years of previous military service they could buy back for approximately $8,000 in deposits. The calculator shows that adding 4 years to the service factor increases their annuity by $3,400/year. At 20 years of expected retirement, the buyback generates $68,000 in additional total annuity payments against an $8,000 cost — an 8.5:1 return.
TSP Allocation vs. Annuity Trade-Off for 20-Year Employee
A GS-13 employee with 20 years of service wants to know whether their FERS annuity alone (approximately $23,000/year at a $115,000 High-3) is enough to retire comfortably at 55. The calculator shows it represents only 37% of current income; they need their TSP to produce $40,000+ annually, which requires a balance of $1 million+ at retirement using a 4% withdrawal rate. This drives a decision to maximize TSP contributions for the remaining 12 years.
Comparison
| Retirement Type | Minimum Age | Minimum Service | Annuity Reduction | SRS Eligible? |
|---|---|---|---|---|
| Immediate (MRA+30) | 55-57 (by birth year) | 30 years | None | Yes, until 62 |
| Immediate (Age 60+20) | 60 | 20 years | None | Yes, until 62 |
| Immediate (Age 62+5) | 62 | 5 years | None (1.1% mult) | No |
| MRA+10 (Deferred options) | 55-57 | 10 years | 5%/yr under 62 | No |
| Early Retirement (VSIP/RIF) | 50 | 20 years | None if agency-offered | Yes, until 62 |
| Disability Retirement | Any | 18 months | None (60% first yr) | No |
Common Mistakes to Avoid
Using current salary instead of High-3 average. The High-3 is the average of the highest 36 consecutive months of base pay, not your current salary. For employees who received a significant step increase or promotion in the final 3 years, High-3 may equal current salary. For employees with stable pay, it equals roughly the average of the past 3 years. Using current salary overstates the annuity.
Forgetting the 5% agency TSP match. FERS employees receive a 1% automatic agency contribution plus a matching contribution up to 4% of salary (matching the employee's first 3% dollar-for-dollar and the next 2% at 50 cents per dollar). An employee contributing 5% receives 5% from the agency — 10% total. Not contributing enough to capture the full match leaves agency money on the table every pay period.
Calculating SRS as the full Social Security benefit. The SRS is a partial benefit approximating only the Social Security earned during federal service. It is not the full SSA benefit and it ends at age 62 regardless of whether the employee claims Social Security. Treating it as equivalent to the full SS benefit overstates early retirement income.
Ignoring FEHB premium deductions from the annuity. Federal employee health benefit premiums continue in retirement but are deducted from the annuity rather than from a paycheck. A federal retiree on a Self+Family FEHB plan pays $450 to $700/month in premiums, directly reducing the net annuity received. Net income planning must subtract these premiums.
Frequently Asked Questions
Accuracy and Disclaimer
This calculator provides estimates of FERS retirement income based on OPM formulas and 2026 TSP contribution limits and Social Security parameters. Actual retirement annuity amounts are calculated by OPM based on verified service records and pay history. TSP projections assume constant returns and contribution levels which will vary. Social Security estimates should be confirmed using your SSA.gov My Social Security account. This calculator is for planning purposes only and does not constitute retirement or financial advice. Consult a federal benefits specialist or OPM directly for official retirement estimates.
Conclusion
FERS retirement planning requires managing three separate systems simultaneously, and the TSP component — which has no ceiling on potential growth — often becomes the most important variable for long-service employees who contribute consistently. After calculating your FERS retirement income, use the Safe Withdrawal Rate Calculator to determine how to draw from your TSP balance without depleting it, and the Roth vs. Traditional IRA Calculator to decide whether your TSP contributions should be traditional (pre-tax) or Roth given your expected retirement tax bracket.
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