Every Monte Carlo retirement calculator gives you a success rate: the share of simulated futures where your money lasts to the end of the plan. The natural next question is what number to aim for. 100%? 90%? Is 75% a failing grade?
There is no official answer, but there is a useful way to think about it: every extra point of safety costs you something, usually monthly spending. Once you see the price, the choice gets much easier.
Try it
What does a higher success rate cost?
You retire today at 65 with a 2,000 a month pension. Slide the success rate you want and see how much you could spend.
Savings at 65
Monthly spending (today's money) vs chance the money lasts to 90
Spending for 90%
4,300 / mo
400 a month less than at 80%
In the futures that fail
age 87
typical age the money runs out; under 1% run out by 80
Typical amount left at 90
857,000
in today's money (median future)
Free, no account needed. Then use Improve on the result to try save more, retire later or spend less.
Retirement Lab engine, 10,000 simulated futures per spending level (steps of 100). 60% stocks / 40% bonds, Balanced outlook (stocks 8%, bonds 4.5%, inflation 2%), spending in today's money after a 20% tax and rising with inflation, pension rising with inflation and taxed at 20%. Plan runs to age 90. Results, not advice.
What each target costs
A 65-year-old with 1 million, retiring now, with 2,000 a month of pension or Social Security. The highest monthly spending (after tax, in steps of 100) that still reaches each target:
| Target | Spending per month | Runs out by 80 | Typical amount left at 90 |
|---|---|---|---|
| 70% | 5,000 | 2.4% | 366,000 |
| 80% | 4,700 | 1.0% | 573,000 |
| 90% | 4,300 | 0.2% | 857,000 |
| 95% | 4,000 | 0.1% | 1,072,000 |
| 99% | 3,500 | 0% | 1,420,000 |
Amounts left at 90 are in today's money, in the median future.
Going from 80% to 95% costs 700 a month, about 15% of the budget, for the whole retirement. Going from 95% to 99% costs another 500. And at 95%, the typical future ends with more money than the retiree started with.
A failure is usually late, not early
The success rate counts a plan that runs dry at 89 the same as one that runs dry at 72. In practice, the failures in a plan like this cluster late. At every target from 70% to 95%, the typical age the money ran out in the failed futures was 86 to 87, and very few had run out by 80.
That matters because you get years of warning. A retiree who checks the plan every year or two will see a bad run coming long before the money is gone, and can spend a little less. The success rate explainer covers why the shape of the failures matters as much as the rate.
How to pick your number
Aim higher if:
- Most of your spending comes from savings, with little pension or Social Security underneath.
- Your spending is hard to cut (rent, care, debt).
- You would rather not revisit the plan often.
- Your plan uses optimistic return assumptions.
You can aim lower if:
- A pension or Social Security covers your essential costs.
- A good part of your spending is flexible (travel, gifts, hobbies).
- You will check the plan regularly and adjust.
- You would rather spend more in your active years than leave a large estate.
For many plans, that lands somewhere between 80% and 95%. Below about 75%, the plan usually needs a change, not just a watchful eye.
The target depends on your assumptions
A success rate is only as good as the returns behind it. The same plan spending 4,300 a month reached 90% with the Balanced outlook (stocks 8%, bonds 4.5% a year) but about 74% with the Cautious one (stocks 6%, bonds 3%). Spending 4,000 dropped from 95% to 85%.
So a sensible habit is to pick a target for a cautious outlook too. If your plan reaches 90% at Balanced and stays above about 75% at Cautious, it has a real margin.
Precision: a few points either way
A success rate from a simulation has some noise. With 1,000 simulated futures (a free run in Retirement Lab), a 90% result could really be about 88% to 92%. With 50,000 (Pro), it moves by a few tenths. The iterations article shows why. Don't treat 89% and 91% as different answers.
Make the trade-off visible
Picking a target is easier when you can see what it buys. To see how long a given amount lasts, try how long will 1 million last?. In the simulator, the Improve panel on your result shows what saving more, retiring later or spending less does to your success rate, with 75%, 90% and 95% targets.
Frequently Asked Questions
- Is a 70% Monte Carlo success rate good enough?
- It can be, if you are willing and able to cut spending when markets go badly. In the example here, a 70% plan failed late (typically around 86) and fewer than 3% of futures ran out by 80. Without that flexibility, or with little other income, most people want more margin.
- Why not aim for 100%?
- Because the last few points cost the most. In the example here, going from 95% to 99% meant spending 500 a month less, and in a typical future the retiree still reached 90 with more money than they started with, in today's money.
- Does a 90% success rate mean a 10% chance of going broke?
- Not quite. It means the money ran out before the end of the plan in 10% of the simulated futures, under the plan's assumptions. In most of those futures it ran out late, and in real life you would see it coming and adjust.
- Should my success rate target change with my market assumptions?
- Yes. A 90% result under optimistic returns is weaker than 85% under cautious ones. In the example here, a plan at 90% with the Balanced outlook dropped to about 74% with the Cautious one.
Find your own success rate
An example plan is filled in - change anything, then open it in the free simulator.
Opens the free simulator with these numbers filled in - check them and run it. Nothing is stored unless you create an account and save.