Monte Carlo Retirement Calculator

About

Plan your retirement with a real Monte Carlo simulation — not a single "expected return" guess.

WHY THIS IS DIFFERENT

Most retirement calculators use a single fixed return (often a hopeful 7%). This extension runs 100 simulation paths with correlated 5-asset returns, then shows you the full range of where your portfolio could land — bad case, median, and good case — under realistic market uncertainty.

The math engine matches quantcalc.app (the free Monte Carlo retirement calculator the QuantCalc team builds for the web) — same lognormal asset-return model, same geometric-vs-arithmetic CME convention handling, same correlation-aware portfolio variance.

WHAT YOU GET (FREE)

✓ Inputs in plain English: age, retirement age, end-of-plan age, portfolio value, contribution, withdrawal, inflation, allocation
✓ Choose your forecast source: JPMorgan LTCMA 2026 (forward-looking) or Historical 1926-2025 (long-run baseline)
✓ 5 asset classes with correlated returns: US Equity, International Equity, Bonds, Real Estate, Cash
✓ Real-vs-nominal dollars toggle (most planners want today's purchasing power)
✓ Success rate — % of paths where your portfolio survives to your end-of-plan age
✓ Percentile ending balances: 10th, 25th, 50th (median), 75th, 90th, plus the mean
✓ Fan chart visualization of P10 / Median / P90 over your full horizon
✓ Re-roll button to test plan stability across independent random draws
✓ Runs entirely locally — no signup, no data leaves your browser

HOW THE MATH WORKS

For each of 100 simulation paths, each year:

GrowthFactor_t = EXP(NORM.S.INV(rand) × σ_p + LN(1 + μ_p))
Balance_t+1   = MAX(0, Balance_t × GrowthFactor_t + CashFlow_t)

Where μ_p is the portfolio's geometric expected return (weighted across your 5-asset allocation) and σ_p is the portfolio standard deviation (correlation-aware, using the standard variance formula). Cash flows: positive contributions while working; negative withdrawals in retirement (inflated each year when Real-dollar mode is on, to preserve your real purchasing power).

This is a lognormal asset-return model — same standard MC engine the QuantCalc web app uses. Verified against the live calculator within Monte Carlo noise.

WHAT'S NOT INCLUDED (and where to find it)

▸ Tax-aware withdrawal sequencing (federal + 51 states)
▸ IRMAA Medicare-surcharge projection
▸ ACA premium-cliff modeling
▸ 10,000-path simulation runs
▸ Stochastic inflation, regime-switching volatility, fat-tailed distributions
▸ Scenario optimizer (lowest-tax withdrawal order)

All available on quantcalc.app — link in the extension popup.

PREFER A SPREADSHEET?

The QuantCalc Retirement Planner is also available as an Excel + Google Sheets spreadsheet on Etsy — same engine, but every cell visible and editable, with 8 CME sources, methodology documentation, and a 60-year horizon. Link in the extension popup.

PRIVACY

No data leaves your browser. The extension uses no external APIs (other than anonymous install-time analytics via Google Analytics 4 — opt-out by disabling the extension). No accounts, no signups, no tracking. Your inputs and results stay local to your machine. See the privacy policy linked in the popup footer.

DISCLAIMER

Educational tool, not financial advice. Monte Carlo simulation gives a range of possible outcomes under the assumptions you input; actual market returns may differ materially. Consult a qualified financial advisor for personalized planning. Independent tool not affiliated with JPMorgan or any other firm whose published research is referenced.

Built by the QuantCalc team — https://quantcalc.app