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FIRE Monte Carlo Simulator
Test your FIRE plan with Monte Carlo and rolling historical retirement simulations using stocks, bonds, cash, inflation, and withdrawals.
Retirement Plan
Starting portfolio
Allocation and rebalancing
Allocation
Allocation must add up to 100%.
Stock Geography
Stock geography must add up to 100%.
Withdrawals
Advanced Settings
Annual fees
Extra cash flows
No extra withdrawals or income added.
Simulation Settings
Model notes
Historical returns cover U.S. stocks, international stocks where available, U.S. bonds, cash, and CPI inflation. International stock observations begin in 1970; bonds remain U.S.-only.
Waiting for simulation
Run the simulation to see success rate, ending portfolio values, and the range of possible outcomes.
Interpret your FIRE simulation
The success rate is the share of simulated paths that do not run out of money before the selected duration ends. It is a stress test built from historical market and inflation years, not a forecast.
Inputs that matter most
- Portfolio value: the investable balance at the start of retirement.
- Stock, bond, and cash allocation: controls how each sampled market year affects the portfolio.
- Stock geography: splits the stock sleeve between U.S. large caps and international stocks.
- Annual spending: the first-year withdrawal before the chosen strategy adjusts it.
- Withdrawal strategy: determines whether spending follows inflation, stays fixed, floats with the portfolio, or uses guardrails.
Common mistakes
- Treating a high success rate as a guarantee.
- Ignoring taxes, fees, account location, and Social Security or pension income.
- Using a spending number that excludes major irregular expenses.
- Assuming rebalancing and spending behavior will be easy during deep drawdowns.
When this estimate can be misleading
The model can be misleading when future returns, inflation, taxes, fees, lifespan, or personal spending shocks differ materially from the historical samples.
Scenarios to try
- Lower spending by 10% and rerun the simulation.
- Compare annual rebalancing with drifting allocations.
- Try 30, 40, and 50 year durations.
- Compare inflation-adjusted withdrawals against guardrails.
Next-step calculators
How the Monte Carlo simulation works
The simulator resamples real annual return and inflation observations, then applies the selected withdrawal rule year by year.
R_{p,t} = w_s R_{s,t} + w_b R_{b,t} + w_c R_{c,t} - f
Each sampled year blends U.S. and international stock returns inside the stock sleeve, then combines stocks, U.S. bonds, and cash using the selected allocation weights before subtracting annual fees.
The historical sample includes U.S. stock, international stock, U.S. bond, cash, and CPI inflation observations. International stock observations begin in 1970, so simulations with any international stock allocation use the overlapping years where that field is available.
Bonds remain U.S.-only. The stock geography split blends U.S. and international stock returns inside the stock sleeve before the overall stock, bond, and cash allocation is applied.
Bootstrap Monte Carlo randomly samples one historical year at a time with replacement. Historical rolling periods use each actual consecutive window available for the selected duration, so higher durations produce fewer simulations. Block bootstrap randomly samples consecutive historical chunks, then stitches those blocks together with replacement.
Each simulated year starts with the planned spending and any extra cash flows. Withdrawals are taken before that year's sampled returns, annual fees are applied to each asset sleeve after returns, and inflation is applied at the end of the year before the next year's inflation-adjusted spending is calculated.
When annual rebalancing is on, the portfolio return is the weighted stock, bond, and cash return for that sampled year. When rebalancing is off, each sleeve grows independently, withdrawals are taken proportionally, and allocations drift.
Scheduled rebalancing happens after the year's return, fee, withdrawal, cash-flow, and inflation steps. If the portfolio is depleted, the simulation records the unpaid withdrawal as a negative balance so shortfalls remain visible instead of stopping at zero.
All chart values are displayed in starting-year dollars by deflating nominal balances by cumulative sampled inflation. If a path depletes, the line continues below zero to show cumulative unmet withdrawals.
FIRE Monte Carlo FAQ
Does this use real market data?
Yes. The simulator embeds annual stock, bond, cash, and inflation observations. Bonds remain U.S.-only; international stock observations are available beginning in 1970.
Why do results change each time?
Bootstrap and block bootstrap runs draw new random historical years or blocks with replacement, so the order and mix of returns and inflation changes. Historical rolling periods are deterministic.
What does percent of portfolio mean?
The first-year spending amount is divided by the starting portfolio value, then that percentage is withdrawn from the current portfolio each simulated year.
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