FIRE Calculator with Monte Carlo Simulation
Enter your savings, how much you invest each year, and what you'll spend in retirement to get your FI number, the age you're likely to reach it, and the chance your portfolio lasts as long as you need it to.
Overview
FIRE (financial independence, retire early) rests on one number: the size of portfolio that can pay your yearly spending indefinitely. Divide your spending by a safe withdrawal rate, commonly 4%, and you have your FI number. Getting there depends on how much you save and how your investments grow.
Average returns alone give a misleading answer, though. Markets don't rise smoothly, and a crash in your first years of retirement can do lasting damage even if later returns are good. This calculator runs your plan through 1,000 different simulated sequences of market returns and reports how often the money lasts, along with the range of likely outcomes at every age. Everything is in today's money, so the figures reflect real spending power.
Examples & Sample Data
Age 30, 50,000 invested, adding 30,000 a year, spending 40,000 in retirement
Return 7%, volatility 15%, inflation 2.5%, withdrawal rate 4%, money lasts to age 90, retire at FI
FI number: 1,000,000 With average returns you reach it at age 50. Chance your money lasts to age 90: 51%
Same plan, but working until 55
As above, retire at a set age of 55
Chance your money lasts to age 90: 73% (up from 51% when retiring at 50)
How It Works
- Enter your age, the age your money needs to last until, your invested savings, and how much you add each year.
- Enter your yearly spending in retirement in today's money, and your safe withdrawal rate. Together these set your FI number.
- Set the expected return, volatility, and inflation. The defaults roughly match a diversified stock-heavy portfolio's history.
- Choose to retire as soon as you reach FI or at a set age, then read the success chance and check the range of outcomes in the chart and table.
Common Use Cases
Setting a FIRE target
Turn your expected retirement spending into a concrete savings goal and a realistic age to reach it.
Stress-testing an early retirement date
See how much the chance of running out of money drops if you retire a few years earlier or spend a little more.
Choosing a withdrawal rate
Lower withdrawal rates mean a bigger FI number but a safer retirement; compare 3%, 3.5%, and 4% for long retirements.
Tips & Best Practices
- The classic 4% rule was based on 30-year retirements. If you retire at 40 and plan to 90, consider 3% to 3.5%.
- A success chance around 85% to 95% is a common target. Aiming for 100% usually means working years longer than you'd ever need to.
- Change one input at a time. The simulation uses the same random sequence each time, so any difference you see comes from that input alone.
Frequently Asked Questions
No. The simulation runs in your browser. The shareable link keeps your inputs in the page address, not on a server.
Each of the 1,000 runs draws a random return for every year from a normal distribution, with your expected return (after inflation) as the average and your volatility as the standard deviation. Contributions are added while you work; in retirement your spending is withdrawn at the start of each year. A run succeeds if any money is left at your plan-to age.
Ups and downs reduce compound growth: a 20% loss followed by a 20% gain leaves you 4% down. So the typical (median) outcome of a volatile portfolio ends up lower than steady average returns would suggest. Set volatility to 0 and every run matches the steady-return path exactly.
It only sets your FI number, shown as a target on the chart. The simulation always withdraws your stated yearly spending, so with a fixed retirement age the success chance depends on spending, not on the withdrawal rate.
No. It's a model built on the assumptions you enter. Real returns aren't normally distributed, and taxes, fees, pensions, and changes in spending all matter. Use it to explore scenarios, and speak to a qualified adviser before making decisions.
Related Tools
Explore more high-performance utilities.