FREE · FINANCE CALCULATORS
Monte Carlo Retirement Simulator.
Will your money last? Run 1,000 to 10,000 random market scenarios to see your probability of retirement success, P10/P50/P90 savings by age, the median age the money runs out and a CSV export.
Market assumptions (editable)
Defaults are US historical averages for 1928–2025 (S&P 500 with dividends and 10-year Treasury bonds), from Aswath Damodaran, Historical Returns on Stocks, Bonds and Bills: 1928–2025 (NYU Stern). They are assumptions, not a forecast: future returns can be lower or higher.
Source of the default assumptions: Aswath Damodaran, Historical Returns on Stocks, Bonds and Bills: 1928–2025 (NYU Stern) (annual returns 1928–2025, checked 2026-10-17). This simulator is an educational estimate, not financial advice: past returns do not guarantee future results. Talk to a licensed adviser before you decide.
Steps to use Monte Carlo Retirement Simulator
Enter your age, retirement age, how long the plan must last, your savings, yearly contribution and yearly withdrawal, and your stock/bond mix. Results update after each change; open “Market assumptions” to change returns, volatility, inflation, the number of simulations or the seed.
How Monte Carlo Retirement Simulator processes your input
Default assumptions from Aswath Damodaran’s 1928–2025 US data (NYU Stern): S&P 500 11.85 % average, 19.40 % volatility; 10-year Treasury bonds 4.82 %, 7.90 %; correlation 0.02; inflation 3.11 %. Seeded mulberry32 generator and Box–Muller draws in a Web Worker, so the same seed gives the same result.
Monte Carlo Retirement Simulator: worked example
Retired at 65 with $1,000,000, withdrawing $40,000 a year (4 %) from a 60/40 portfolio until 95 with the default assumptions: about 92 % of 5,000 simulations (seed 2026) still have money at 95; with $60,000 a year, about 54 %.
How to run a Monte Carlo retirement simulation
- Enter your current age, the age you plan to retire and the age the money must last until.
- Enter your current savings, what you add each year until retirement and what you plan to take out each year in retirement, both in today’s money: the simulator raises them with inflation every year.
- Choose the share of stocks; the rest is in bonds and the mix is rebalanced every year.
- Read the probability of success, the median age at which the money runs out in the failed simulations and the P10 / P50 / P90 chart. Download the CSV for every age.
Example with the default assumptions (5,000 simulations, seed 2026): at 40 with $250,000, adding $15,000 a year until 65 and withdrawing $60,000 a year until 95 with 60 % stocks, 82.4 % of the simulations still have money at 95. Retired at 65 with $1,000,000, a $40,000 withdrawal (4 % the first year) succeeds in 92.1 % of the simulations, and $60,000 (6 %) in 53.9 %.
How to read P10, P50 and P90
Each simulation draws a different sequence of yearly returns. At every age the simulations are sorted: P50 is the median, P10 the value that 10 % of the simulations end below (bad markets) and P90 the value only 10 % exceed. The shaded band therefore holds 80 % of the outcomes. All amounts are in today’s money, so they can be compared with your spending now.
A success rate is not a guarantee: it only says how often the plan worked under the assumptions you entered. Many plans include spending a little less in bad years; this simulator keeps the withdrawal fixed, which is a cautious view.
Default assumptions and their source
| Assumption | Default | Meaning |
|---|---|---|
| Stocks: average yearly return | 11.85 % | S&P 500 with dividends, 1928–2025 |
| Stocks: volatility | 19.40 % | Standard deviation of the yearly returns |
| Bonds: average yearly return | 4.82 % | US 10-year Treasury bond, 1928–2025 |
| Bonds: volatility | 7.90 % | Standard deviation of the yearly returns |
| Stock–bond correlation | 0.02 | Almost independent over the period |
| Inflation | 3.11 % | US consumer prices, 1928–2025 average |
The figures were computed from the annual data of Aswath Damodaran (NYU Stern), “Historical Returns on Stocks, Bonds and Bills: 1928–2025”. They are US nominal averages: lower them to test a more cautious future or to reflect fees. Returns are drawn from normal distributions; real markets have fatter tails, so the worst cases may be worse than the P10.
To project the savings phase in more detail use the Retirement Contributions Projection; to find the amount you need, the FIRE Calculator; to see what inflation does to a sum, the Inflation Scenario Calculator; for steady growth without randomness, the Compound Interest Projection; and to estimate a US Social Security check to subtract from your withdrawal, the Social Security COLA Calculator 2027.
Questions about Monte Carlo Retirement Simulator
What is a Monte Carlo retirement simulation?
It replays your plan thousands of times with random yearly returns drawn from the average and volatility you set, and counts how often the money lasts until the age you chose.
What is a good probability of success?
There is no official threshold. A higher rate means more safety but less spending; many people test several withdrawals and keep one they could adjust if markets are bad early in retirement.
Can I test the 4 % rule?
Yes: enter your current age as the retirement age, your savings, and 4 % of them as the yearly withdrawal. The simulator keeps that amount fixed in today’s money each year, like the rule.
Why do two runs give the same result?
The random numbers come from a seeded generator, so the same inputs and seed always give the same result. Change the seed to see another set of simulations.
Are taxes and Social Security included?
No. Enter withdrawals after subtracting pensions or Social Security, and remember that taxes and fees reduce what you can spend. This is an educational estimate, not financial advice.
Is Monte Carlo Retirement Simulator free, and do I need an account?
Yes. This tool is free to use in your browser without an account. Processing takes place on your device.
What are the limits and what should I check?
Educational estimate, not financial advice. Yearly steps, normally distributed returns, yearly rebalancing; no taxes, fees, Social Security or pension (lower the withdrawal by that income). Past returns do not guarantee future results. Runs in your browser. Review the result before using it in your work.
Is my input sent to a server?
Your input is processed in your browser and is not uploaded by this tool. Files and pasted text are cleared when the page is refreshed. Normal website requests are still required to load the page and its libraries. Read the privacy explanation.