Monte Carlo Retirement Calculator
Run thousands of random return paths to see how often a portfolio could last through retirement.
Quick answer
Monte Carlo retirement analysis runs many random return paths using your expected return and volatility, applying inflation-adjusted withdrawals each year. Success probability is the share of paths where the money lasts.
Monte Carlo Retirement Calculator
Rises with inflation; modelled as constant in real terms.
Average yearly return after inflation.
Same inputs and seed give the same result.
Success Probability
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Median Ending Balance
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10th Percentile Ending
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90th Percentile Ending
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Initial Withdrawal Rate
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Portfolio Balance by Percentile (today's money)
| Year | 10th (₹) | 25th (₹) | Median (₹) | 75th (₹) | 90th (₹) | Paths with money left |
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Assumptions & method
- Each year: the withdrawal is taken at the start of the year, then the remaining balance earns that year's random return. A path fails when a withdrawal cannot be paid in full.
- Yearly returns are lognormal and independent, with arithmetic mean equal to the expected real return and standard deviation equal to the volatility you enter. Returns cannot fall below −100%.
- Random numbers come from a seeded mulberry32 generator, converted to normal values with the Box-Muller transform, so results are repeatable.
- Success probability = paths with money left after the final withdrawal ÷ total paths. Percentiles are taken across paths for each year; failed paths count as zero.
- Everything is in real (inflation-adjusted) terms. Taxes, fees, changing spending, other income and fat-tailed or correlated returns are not modelled.
Results are estimates based on the figures you enter. They are not guarantees and not financial advice.
Why a Monte Carlo simulation
A fixed average return hides the fact that markets move up and down, and bad early years hurt a retirement portfolio more than bad later ones. A Monte Carlo simulation addresses this by running many random return paths. Each path draws a return for every year from a distribution with the expected return and volatility you set, applies your inflation-adjusted withdrawal, and records whether the money lasts. The share of paths that last is the success probability, and percentile bands show how widely outcomes spread. It is a model of risk, not a prediction.