What is covered well
FERS timing, household cash flow, taxes, TSP drawdown, FEHB, Medicare, and state taxes are all in scope today.
Assumptions, Coverage & Limits
The output is only as trustworthy as the scope and assumptions behind it.
This page is the canonical description of what FERSCalc models today, what it does not, and where results should be treated as directional planning context rather than final truth.
FERSCalc is not affiliated with OPM or any federal agency, and it does not replace official estimates or professional tax, legal, or financial advice.
What still needs caution
Edge cases such as part-time service prorating, self-employment income and tax detail, Roth basis tracking, and state-specific municipal-bond exemptions remain simplified or excluded.
How to use the result
Use the output to compare scenarios and sharpen questions, then confirm major decisions with official sources and qualified advisors.
Modeled Today
Retirement income and timing
The main projection covers supported FERS voluntary annuity paths, including frozen-at-separation service records, immediate first-of-next-month commencement, MRA+10/postponed/deferred choices, sick-leave computation credit, 6C-covered service, the FERS supplement, survivor elections, and Social Security claiming-age scenarios. Verify retirement records and final elections with your agency and the relevant program administrator.
Taxes and paycheck bridge
Federal tax estimates, state income-tax models, working-side FERS contribution drag, and tax-adjusted retirement cash flow appear in the year-by-year output. They are not tax returns or certified future-law calculations. Local city, county, and municipal income taxes are not modeled.
TSP drawdown and stress testing
Deterministic TSP withdrawals are modeled in the core projection, with Traditional and Roth balances tracked separately. Pre-retirement employee contributions are capped by the current modeled TSP elective-deferral and catch-up limits, with agency automatic and matching contributions tracked separately. Four withdrawal-source modes are supported: Traditional-first, Roth-first, Proportional, and a threshold-aware guardrail mode. Fixed annual in-plan Roth conversions after retirement are also modeled. When more than one withdrawal-source mode applies, results rank them on projected lifetime federal tax plus Medicare drag. The threshold-aware mode is a year-by-year guardrail heuristic, not a full lifetime optimizer. Optional historical replay (Results → Stress) runs additional deterministic projections from bundled CPI and TSP fund-return data on your timeline; it is illustrative and may truncate if history ends before your horizon. See the Monte Carlo and Historical Replay scope notes below.
Health and household context
FEHB premiums, Medicare Part B, IRMAA, spouse or partner scenarios, survivor pension and Social Security survivor estimates, filing-status changes on death, TSP spousal transfer, and exportable reporting are represented in the current product. The annual income ledger consistently includes FERS pension and supplement, survivor pension, wages, TSP distributions/conversions, Social Security, and entered tax-exempt interest in the applicable cash-flow, tax, provisional-income, and MAGI calculations. Household eligibility, death timing, survivor taxation, and health-coverage transitions contain material simplifications.
Coverage Today
FERS tiers and 6C coverage
FERS Classic, FERS-RAE, FERS-FRAE, and 6C special-category retirement coverage are supported. Standard contribution tier can auto-detect from service start date or be manually overridden for edge cases. The standard tier changes paycheck deductions and take-home comparisons while working, while 6C changes retirement eligibility and pension formula.
State-tax coverage
The model includes a 2025 state income-tax baseline for all 50 states and DC: 42 jurisdictions with income tax and 9 no-income-tax states. This is planning coverage, not independent state-rule certification; simplifications and omissions remain.
See per-state FERS, TSP & SS treatment →Calculator assumptions you can change
Inflation, salary growth, FEHB premium inflation, TSP returns, COLA, mortality years, projection horizon, and historical stress-test presets are exposed as scenario assumptions.
See the Field Guide for input mechanics →Known Gaps The important missing pieces should be easy to spot. 13 current gaps are tracked here, including part-time service prorating, Roth basis handling, local-tax exclusions, and survivor-edge simplifications.
- Future retirement-date salary, High-3, and TSP balances use the calculator’s annual timing convention rather than your agency payroll, personnel, or account record. Verify final amounts with official records.
- The supported FERS voluntary pathways use frozen service, OPM-style month calculations, and selectable commencement dates, but do not cover every retirement authority, appointment type, military-service rule, LWOP rule, disability path, or agency-specific record correction.
- Federal tax, Medicare, and state calculations use a mix of known rule-year constants and future projections. They are not certified tax calculations or tax filings.
- FERS Special Retirement Supplement, Social Security, survivor, and health-coverage timing contain known eligibility and timing simplifications.
- Monte Carlo varies TSP returns only and reports balance survival; it does not model dynamic household spending or determine that retirement is affordable.
- CSRS and CSRS-Offset are not modeled.
- Part-time federal service uses entered actual and full-time hours for OPM-style proration when supplied; otherwise schedule percentage is a planning proxy. OPM records can include nonpay-status rules, so confirm the official proration factor with your agency.
- Roth TSP basis is not tracked — when the 5-year requirement is not met, the entire Roth withdrawal is treated as taxable rather than only the earnings portion. This is conservative but may overstate taxable income.
- Tax-exempt interest is a separate modeled state-tax source, but bond issuer/state is not collected. It therefore uses a conservative general-income state treatment rather than an in-state municipal-bond exemption. The exported state source base is before state-specific exemptions and deductions.
- Local city, county, and municipal income taxes are intentionally excluded from the model.
- Survivor Social Security uses a simplified age-based reduction factor rather than the full SSA survivor benefit computation.
- FEHB continuation rules after a spouse's death are not modeled — premiums remain unchanged in the projection.
- Remarriage effects on survivor pension eligibility and filing status are not modeled.
Rule Sources & Currency
Known source dates are visible; future estimates are not presented as current law.
These links identify the governing source or verification location for the current model. Before each production build, a provenance gate checks for missing source metadata, overdue annual reviews, and stale exact-year tables. That gate and a source catalog are not independent calculator certification; official-source fixture packs remain in progress.
Federal income tax
2025 baseline; future years are currently projected, not certified
IRS 2026 inflation-adjustment release →Medicare premiums and IRMAA
Modeled baseline requires annual CMS verification
CMS Part B premiums and deductibles →FERS Special Retirement Supplement
2025–2026 known earnings-test amounts; future amounts are projected
OPM CSRS/FERS Handbook, Chapter 51 →Social Security earnings-test amount
2026 lower exempt amount: $24,480
SSA retirement earnings-test table →State income tax
2025 rule baseline; not independently certified for every jurisdiction
FERSCalc state-tax guide and per-state model notes →Baked-In Assumptions The projection starts from a clear rule set. Federal tax rules, state-tax baselines, FEHB growth, TSP return assumptions, COLA handling, and Roth qualification rules are all defined here.
- Federal income-tax brackets and standard deductions use source-dated IRS rule sets for 2024 through 2026, including the final 2025 OBBB standard deductions and the temporary 2025–2028 enhanced senior deduction. Years after 2026 are projected from the 2026 rule set using the scenario inflation assumption; projected years are not enacted-law tax estimates. The annual income ledger provides the model’s AGI/MAGI input, including tax-exempt interest for Social Security provisional income and IRMAA. Schedule 1-A uses its separate MAGI definition rather than the IRMAA measure.
- Future retirement-date salary, High-3, and TSP-balance accumulation follows the documented annual timing convention. Treat the result as a planning estimate and confirm final amounts with agency and account records.
- State-tax rules use a 2025-law baseline, but most state brackets are held constant rather than inflation-indexed year by year. State coverage has not yet received independent jurisdiction-by-jurisdiction certification.
- The Social Security wage base is indexed forward from the 2025 base ($176,100) using a fixed 3.5%/yr average-wage-index (AWI) growth assumption and simple rounding rather than SSA’s official wage-base rounding convention. Federal tax and Medicare baseline constants are reviewed against annual IRS, SSA, and CMS releases before each tax year.
- FEHB premiums grow at the scenario FEHB premium inflation rate.
- Entered salary and TSP balances are valued at the start of the current calendar year. The deterministic projection applies its annual timing convention through every working year and the worked portion of the retirement year before it initializes retirement withdrawals. It is not a payroll, personnel, or account statement.
- For supported FERS voluntary paths, detailed service periods are calculated with OPM’s 30-day month / 360-day year convention and frozen at separation. Immediate annuities start the first day of the next month; MRA+10 and deferred records use a selected first-of-month legal commencement date at least two days before age 62 for the permanent full-month age reduction. Unused sick leave is converted after eligibility and 6C tiers and is excluded from deferred annuities. Actual/full-time hours drive part-time proration when entered; schedule percentage is the fallback. Creditable military service can add formula service but cannot satisfy the five-year civilian-service minimum.
- Roth TSP withdrawals apply the IRS 5-year qualification rule when a first contribution year is provided. When the year is left blank or the account is already qualified, earnings are treated as tax-free. Basis is not tracked — unqualified withdrawals conservatively treat the entire amount as taxable.
- Social Security benefit amounts are calculated using whole-year claiming ages. Benefits claimed in a month other than your birthday month may differ from the calculator estimate by roughly 1–2%.
- Standard FERS pension COLAs are deferred until age 62 unless the person is modeled as 6C special-category. Once eligible, FERS COLA follows the standard rule structure: full CPI up to 2%, capped at 2% for 2% to 3%, and CPI minus 1% above 3%.
- The FERS Special Retirement Supplement is not inflation-adjusted or COLA-adjusted. It remains flat until it stops at age 62, subject to any modeled earnings-test reduction.
- TSP employee contribution limits use explicit IRS/TSP constants for 2024 through 2026, including age-50 catch-up and the SECURE 2.0 higher catch-up window for ages 60 through 63. Future years currently hold the latest modeled limit constant until the annual constants refresh updates them.
- Projection length is based on the chosen simulate-through age, with a minimum window so short scenarios still produce usable output.
- When historical stress replay is enabled, CPI and TSP fund returns for that run come from the app’s bundled annual dataset (not from your static TSP return assumptions). The primary projection row in the calculator still uses those static rates unless you are looking at the Stress tab outputs.
Monte Carlo Scope Useful stress test, not full-world uncertainty modeling Monte Carlo randomizes TSP investment returns only. The rest of the household cash-flow model stays deterministic.
- Monte Carlo randomizes annual TSP investment returns only.
- Pension, Social Security, FEHB, Medicare, taxes, and other cash-flow rows stay fixed from the deterministic scenario.
- The default portfolio statistics represent a blended TSP allocation assumption rather than your exact holdings unless you interpret them that way yourself.
Historical Replay Scope Bundled history on your timeline — illustrative, not predictive Results → Stress runs optional extra projections using annual CPI and fund-return sequences from the app’s history file, separate from Monte Carlo and from your long-run static return assumptions.
- Historical replay uses the bundled annual dataset in the app (CPI and per-fund TSP returns). It is not your personal account history and not a guarantee of future results.
- Replay aligns the chosen history sequence to your projection timeline; calendar labels follow your plan while economics follow the selected slice.
- L Fund glide during replay is approximated from published glide-path weights.
- If the dataset ends before your full simulate-through horizon, stress paths stop early and the UI should indicate truncation.
Use Directionally Some scenarios should sharpen your questions, not settle the decision. Treat the result more cautiously when future law, unsupported retirement systems, or timing-sensitive edge cases are driving the answer.
- When your situation depends on future law, tax, Medicare, or policy changes that are not known yet.
- When you are in a retirement system or employee category the calculator does not yet support directly.
- When small timing details matter enough that integer-age Social Security claiming or simplified state-tax handling could move the answer materially.
- When you are using Monte Carlo output as if it were a forecast of total household uncertainty rather than a TSP-return stress test.
- When you are treating historical replay output as a prediction of future markets or exact fund performance rather than a directional illustration with bundled, imperfect proxies.
Evergreen Note
This page changes whenever coverage changes, so what you read here should match what the calculator actually does today.
Use FERSCalc to compare options, then confirm major decisions the right way.
The right workflow is to use the calculator for scenario planning, then verify final retirement timing, tax treatment, and agency-specific questions with official sources and qualified advisors.