Short answer: no one knows what markets will do, so this simulator runs your plan through 10,000 possible futures and counts how often the money lasts. With $1,000,000 saved and $40,000 a year of spending for 30 years, it lasted in 73.8% of futures under our starting assumptions, and spending of about $33,245 a year lasted in 90% of them. Change any number to test your own plan.
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How the simulation reached your result.
Year-by-year range of balances
| Year | Bad luck (10th pct) | Middle | Good luck (90th pct) | Still funded |
|---|
How it works: each of 10,000 futures draws a random return for every year, using the averages and swings above (yearly returns follow a lognormal shape, and stocks and bonds move independently). Spending comes out at the start of each year. A future “fails” the first year the savings can’t cover it. Real markets can do worse than any model, and this tool leaves out taxes, Social Security and other income. Educational estimate only, not financial advice. Your numbers never leave this page.
How this simulator works
Each of the 10,000 futures draws a random return for every year of your retirement, using the average return and typical yearly swing you enter for stocks and for bonds. Yearly returns follow a lognormal shape (they can fall a lot but never below -100%), and stocks and bonds move independently. Each year your mix is reset to your chosen split, fees come off, and your spending is taken out at the start of the year. A future fails the first year your savings cannot cover that year’s spending.
Everything is in today’s dollars. The returns you enter are after inflation, so your spending keeps the same buying power every year and you do not need to guess an inflation rate.
The “spending that lasts” figure is found by searching whole-dollar amounts on the same 10,000 futures until it finds the highest spending that lasts in your target share of them (90% unless you change it).
Why there is a simulation number
The futures are random, but they come from a numbered sequence. The same simulation number always gives the same 10,000 futures, so a shared link shows exactly what you saw. Press “Try another” to draw a different set and see how much the estimate moves by chance alone.
Worked example
$1,000,000 saved, $40,000 a year for 30 years, 60% stocks and 40% bonds, 0.2% yearly fees, simulation number 1:
- Chance the money lasts: 73.8% (7,375 of 10,000 futures)
- Spending that lasts in 90% of futures: $33,245 a year
- Middle ending balance: $363,694; in a bad-luck future (10th percentile) the money runs out
About the starting assumptions
Stocks start at a 5% average yearly return after inflation with a 17% typical swing, and bonds at 1.5% with a 6% swing. These are round-number assumptions, not a forecast, and they are not taken from any market dataset. Lower returns or bigger swings make every plan look riskier, so try a few versions before you rely on one.
FAQs
What success rate should I aim for? There is no single right answer. A higher target means lower safe spending; many people test 80% to 95% and plan to adjust spending if markets go badly.
Does it include Social Security or pensions? No. Enter only the spending your savings must cover, after subtracting other income you expect.
Does it include taxes? No. If withdrawals will be taxed, include the tax in your spending figure.
Why does the result change when I change the simulation number? Each number draws a different set of 10,000 random futures. Small moves (a percentage point or so) are chance; a plan whose result swings a lot is close to the edge.
Disclaimer
Educational estimate only, not financial advice. Real markets can do worse than any model. All the math runs in your browser and your numbers never leave this page. See how we build and check our calculators.