Federal Retirement Benefit & Monte Carlo Success Calculator

Annuity. FERS: 1% of high-3 × years of service, or 1.1% if you retire at 62+ with 20+ years, per OPM's computation rules. Special provisions (LEO/FF/ATC): 1.7% × first 20 years + 1% for the rest. CSRS: 1.5% × 5 + 1.75% × 5 + 2% × remaining years. Unused sick leave is converted at 2,087 hours per year and added to the computation only. MRA+10 retirements are reduced 5% for each year under 62 unless postponed. The CSRS basic annuity is capped at 80% of high-3, though credit for unused sick leave is exempt from that ceiling, per OPM’s CSRS computation rules. Fewer than 5 years of creditable service means no annuity is payable at all.

When the annuity starts. If you separate before you qualify for an immediate annuity — or postpone an MRA+10 — nothing is paid until the deferred commencing age (generally 62, or 60 with 20 years, or your MRA with 30 years). The simulation pays $0 during that gap and makes your TSP carry the spending, which is the single largest risk in an early separation.

Survivor benefit. Under FERS a 50% survivor annuity reduces your gross by 10% and a 25% election reduces it by 5%. CSRS uses a dollar formula instead: 2.5% of the first $3,600 of the annuity plus 10% of the remainder for a full election, and half that for a partial one, per 5 CFR 831.611.

FERS Annuity Supplement. Whole years of FERS civilian service ÷ 40 × your age-62 Social Security estimate, paid until age 62, per 5 CFR 842.504. It receives no COLA and is subject to an annual earnings test: $1 is withheld for every $2 of wages above the Social Security exempt amount, $24,480 for 2026 per SSA. Enter expected post-retirement wages and the tool applies that reduction. Special-provision retirees are exempt from the test until they reach their MRA.

COLAs. FERS annuities use the "diet COLA": full CPI-W when inflation is 2% or less, capped at 2% between 2–3%, and CPI-W minus 1 point above 3% — and generally none before age 62, as described by the Congressional Research Service. Special-provision retirees receive COLAs immediately. CSRS and Social Security receive the full CPI-W.

Social Security timing. Your age-62 figure is grossed up to a full-retirement-age amount (age 67) and then adjusted: 5/9 of 1% per month for the first 36 months of early claiming, 5/12 of 1% per month beyond that, and 8% per year of delayed credits after FRA.

Monte Carlo. Each trial draws a fresh sequence of annual stock returns (9.0% mean, 17.5% standard deviation), bond returns (4.3% mean, 6.0% standard deviation) and inflation (2.5% mean, 1.4% standard deviation), lightly correlated and fat-tailed. Health premiums grow at their own rate, separate from general inflation, because FEHB has historically risen faster than CPI. Unused annual leave is paid out in cash at separation and taxed at the marginal rate that applies on top of a final year of salary. Withdrawals fill the gap between guaranteed income and your spending goal plus premiums and taxes. A trial "succeeds" if the portfolio is never exhausted while you are alive.

Income tax. Your spending goal is treated as an after-tax number, so each year the tool solves for the gross withdrawal that covers spending, premiums and the tax on itself. Tax is computed on the real 2026 rate schedule and standard deduction from IRS Rev. Proc. 2025-32 — seven brackets from 10% to 37%, a $16,100 single / $32,200 joint standard deduction, the extra $2,050 / $3,300 deduction at 65 and over, and the temporary $6,000 / $12,000 senior deduction, which phases out 6 cents per dollar of income above $75,000 / $150,000 and expires after tax year 2028. Bracket edges and deductions are indexed to the simulated inflation path, as the IRS indexes them in practice. Social Security is taxed on the statutory provisional-income formula: nothing below $25,000 / $32,000, up to 50% between there and $34,000 / $44,000, and up to 85% above that, per the Congressional Research Service. Those four thresholds were written into law in 1983 and 1993 and are deliberately not indexed here, because they are not indexed in law either, so a rising share of your benefit becomes taxable over time. State tax is applied as a flat rate on ordinary income and never on Social Security, which no state currently taxes. The FERS or CSRS annuity is treated as fully taxable; the small tax-free portion representing a return of your own contributions is ignored, which makes the estimate slightly conservative.

Required minimum distributions. Under SECURE 2.0 the first distribution year is age 73 if you were born from 1951 through 1959 and age 75 if you were born in 1960 or later. Each year the traditional balance is divided by the life-expectancy factor in IRS Publication 590-B Uniform Lifetime Table (27.4 at 72, 24.6 at 75, 16.0 at 85) and that amount is withdrawn and taxed whether or not you need it. Anything above your spending need is reinvested in a taxable account, whose growth is then taxed as ordinary income each year. Roth balances are exempt from lifetime RMDs, including Roth TSP since 2024, so the Roth share you enter reduces forced income.

Medicare premium surcharges. From age 65 the tool adds the income-related monthly adjustment amount to your costs, using the 2026 tiers published by CMS: nothing at or below $109,000 single / $218,000 joint, then per-person Part B surcharges of $81.20, $202.90, $324.60, $446.30 and $487.00 a month, plus Part D surcharges of $14.50 to $91.00. Crucially the surcharge is set from the tax return filed two years earlier, so income at 63 decides the premium at 65 and a conversion echoes forward two years. Surcharges are counted per enrolled person, so a joint return is charged twice; income thresholds are indexed to the simulated inflation path except the top pair, which statute holds flat at $500,000 / $750,000. The surcharge dollars grow at the health-premium rate you enter rather than at CPI, because Part B has historically outrun general inflation. Only the surcharge is added here, not the standard $202.90 Part B premium — include that in the FEHB figure if you plan to enrol, so it is not counted twice.

Roth conversions. The planner converts traditional TSP to Roth in each year from retirement until the age you choose, taking exactly enough to fill income to the top of your target bracket. Tax on the conversion is paid from the portfolio in the same year, which is why an aggressive target can lower the odds of success even while it lowers lifetime tax. Because each converted dollar can pull up to 85 cents of Social Security into taxable income, the available room is solved rather than assumed. Converted balances move to the Roth bucket, where they are exempt from lifetime required distributions, so the forced income at 73 or 75 falls. The optional Medicare guard caps conversions from age 63 onward so income stays under the first surcharge tier; without it the tool will happily cross a tier and then shows you the bill. The TSP itself only began permitting in-plan Roth conversions on 28 January 2026, under a final rule from the Federal Retirement Thrift Investment Board, with a $500 minimum per conversion and a limit of 26 a year. Conversions are irreversible.

Why the leftover balance is taxed. A traditional balance you never spend is not an asset, it is a deferred tax bill: someone pays ordinary income tax on every dollar, either you in your nineties or your heirs inside the ten-year window the SECURE Act imposes on most inherited accounts. A comparison that ignores that will always conclude conversions are a waste, because it counts the tax a conversion triggers and none of the tax it avoids. So the all-in figure charges the rate you enter against whatever traditional money is left when the plan ends, and the whole verdict swings on that one number. Set it near your own future marginal rate if you expect to spend the money, near your heirs’ rate if you expect to leave it, or to zero if it is going to charity.

How long you live. By default each trial draws its own age at death year by year from the SSA 2023 period life table used in the 2026 Trustees Report, capped at 105. This is a more honest test than a single fixed age, but read the headline carefully: a trial in which you die at 74 with money left over counts as a success, so modelling longevity raises the success rate relative to assuming everyone reaches 95. That is why the panel also reports success among only those trials that reach age 90, which is the number that matters if you are healthy. The blended mortality basis averages the male and female rates. Choosing a fixed age instead makes the tool behave like a conventional planner and is the stricter test.