FIRE Monte Carlo simulator

How it works

The simulator takes your assets, how much you invest and how much you want to spend, and runs the plan through thousands of different futures. The success probability is the share of scenarios in which the money lasts to the final year you chose.

• Monte Carlo: random returns with the mean and volatility you pick. Useful to test cautious or optimistic assumptions.
• Historical: real sequences from 1928 to 2025, each starting in a different year, so real crashes and sequence-of-returns risk are included.
• Spending models: a fixed amount, a percentage of the portfolio, or spending that declines with age.
• Pensions and income: add the Italian state pension, an annuity or a recurring expense such as a mortgage. One-offs (inheritance, buying a home) are in the Advanced step.

Reading the result

Above 90% the plan holds in almost every scenario; between 70% and 90% it is worth strengthening (more saving, lower spending or one more working year); below 70% it is fragile. The Compute optimisations button finds the earliest year you can stop and the maximum sustainable spending.

Limits to know

The historical series is the S&P 500 in US dollars: it does not represent a global portfolio in euros and does not include tax on returns. Keep amounts and returns consistent (today's euros with real returns, or everything nominal). For a quick first estimate use the FIRE simulator with the Italian state pension.

All the calculation runs in your browser: no data is sent to or stored by us.