What Is a Good Monte Carlo Success Rate for Retirement?

You ran your plan and got a number. Maybe 74%. Maybe 91%. Now you want to know if it's any good. Here's the short answer: most published guidance puts a good Monte Carlo success rate for retirement somewhere between 70% and 95%. Below 70%, most advisors get uneasy. Above 95%, you may be giving up spending you could safely afford.

The number alone doesn't tell the whole story, though. What counts as "good" for you depends on how flexible your spending is, how much guaranteed income you have, and what the model assumed in the first place. Let's go through it.

What a Monte Carlo success rate actually means

"Monte Carlo" sounds technical. The idea is simple.

An average-return projection assumes the market does the same thing every year. Real markets don't. A Monte Carlo simulation runs your plan through hundreds or thousands of possible futures instead. Some have strong markets, some have crashes early in retirement, some have stretches of high inflation. Then it counts how many of those futures leave you with money at the end.

Run 1,000 futures. If your money lasts in 850 of them, your success rate is 85%. In the other 150, the portfolio ran out at some point before the plan ended.

That's all it is. A probability, not a promise.

One detail matters a lot. In most tools, "success" just means ending with at least $1 left. It doesn't care whether you finish with $1 or $2 million. "Failure" covers everything from running out at 75 to running $1 short in the final year. We'll come back to why that matters.

What is a good Monte Carlo success rate for retirement?

There's no official standard, but the guidance clusters in a fairly tight range:

That last row is worth a closer look. Morningstar's 2025 research puts the safe starting withdrawal rate at 3.9%, defined as the rate where money is still there in 90% of simulated outcomes over a 30-year retirement. Even the best-known "safe" spending rule is built on a success rate, and it isn't 100%. (Source: Morningstar, The State of Retirement Income 2025, December 2025.)

So if your score is somewhere between the high 70s and the mid 90s, you're inside the range most professionals treat as reasonable.

Why 100% isn't the goal

A higher number feels safer, so it's natural to want 99%. But T. Rowe Price and Income Lab both warn that a score near 100% can mean you're spending too little.

Think about what 99% requires. Your plan has to survive almost every bad future the model can come up with, including the rare worst cases. To get there, you hold back spending in your 60s and 70s, and in most futures you never needed to. You'd likely die with a large balance you could have used for travel, family, or simply working fewer years.

That's why the advisor guardrail practice above treats 99% as a cue to raise spending. Underspending is a risk too. It's just quieter.

A "failure" is usually a pay cut, not a cliff

This is the part most people miss. Real retirees don't keep spending on autopilot until the account hits zero. When markets fall, they adjust.

Because of that, some planners have suggested renaming the outcomes. Kitces.com proposes calling it a "probability of adjustment" instead of a probability of failure. White Coat Investor puts it plainly: a 90% success rate really means about a 10% chance you'll need to adjust your spending, not a 10% chance you'll go broke.

Kitces goes further, arguing that a score as low as 50% may be reasonable for retirees who are genuinely willing to cut spending when needed. That isn't a target to aim for. It's a reminder that flexibility changes what the number means.

Retirement researcher David Blanchett points out the metric's biggest blind spot: it ignores how big the shortfall is. Being $1 short in the last year of your plan counts as a failure, exactly like running dry a decade earlier. So when you look at your score, also ask when the failing futures run out and by how much. A plan that only fails at 93 is very different from one that fails at 78.

How your situation changes your target

The research gives a range. Where you belong in it depends on your circumstances. This is a framework for thinking, not personal advice.

Your score is only as good as its assumptions

Two people can enter the same plan into two different tools and get 72% in one and 88% in the other. Neither tool is broken. They just assume different things about returns, volatility, inflation, and how long you'll live. Scores don't transfer cleanly from one tool to another.

The model type matters too. An Income Lab analysis found that "traditional" Monte Carlo models had the most error compared with real-world outcomes, while historical and regime-based models did better.

Three assumptions are worth checking in any tool you use:

1. How long the plan runs. About one out of every three 65-year-olds may live to at least 90 (Source: Social Security Administration, Retirement Information for Medicare Beneficiaries, 2026). A plan that stops at 85 quietly bets against a third of retirees. There's a trade-off, though. Kitces.com shows that for a 65-year-old couple over a 30-year horizon, a 90% result works out to roughly 98% overall success once you account for the chance of dying earlier. A long horizon is conservative by design, so a slightly lower score over a long horizon may be fine.

2. Health care costs. Fidelity estimates a 65-year-old retiring in 2025 will need $172,500 for Medicare premiums, deductibles, and prescriptions over retirement, and that figure doesn't include long-term care (Source: Fidelity Investments, 2025 Retiree Health Care Cost Estimate, July 2025). That's a real line item. If your tool ignores it, your score is flattering you.

3. Spending. It's the input with the most influence on the result, and many people have never pinned it down. EBRI's 2025 Retirement Confidence Survey found only 52% of workers have estimated the monthly income they'll need in retirement (Source: EBRI/Greenwald, Retirement Confidence Survey 2025, Fact Sheet 3). If your monthly spending figure is a guess, so is your success rate.

What to do at each score

Here's how to read your number, based on the guidance above:

• Below 70%. Most advisors would call this too low for a typical retiree. Test the main levers one at a time: spend a little less, work a bit longer, or change when you claim Social Security. Watch how much each one moves the score.
• 70% to 80%. Can work if your spending is flexible. Decide in advance what you'd cut if markets turn against you, so a bad year doesn't turn into a panic.
• 80% to 95%. The zone most published guidance points to. Keep monitoring.
• Near 99%. You may be underspending. Consider whether retiring sooner or spending more fits your life better.

Tracking your score over time

Your score will move. A bad market year will pull it down. That's expected, since the simulation already included futures with bad years. One dip isn't a warning sign.

What matters is the trend. If your score keeps sliding toward the 70% area, that's the signal advisors use to recommend cutting spending. If it keeps climbing toward 99%, it's the signal to spend more. Check once a year, and again after any big change like a market drop, a health event, or a change in plans.

Run your own numbers

Benchmarks only help once you know your own number. Monte Climb runs your age, savings, and monthly spending through 1,000 simulated futures and gives you a success rate. Three numbers. It runs in your browser, and nothing is saved until you say so. Plans run to age 95 by default, and the engine charges Medicare premiums and income-based surcharges year by year instead of using a flat guess.

Then you can ask William, our AI planner, what the result means: "Am I on track?" "Can I retire at 62?" "What's a sustainable spend?" He shows his work.

It's planning software, not advice. It gives you a probability, not a promise, and a much better starting point than a guess.

Show my answer →

Frequently asked questions

What is a good Monte Carlo success rate for retirement?

Most published guidance falls between 70% and 95%. T. Rowe Price suggests an 80% to 95% 'Confidence Zone,' while Mission Wealth treats 70% as the minimum and prefers 85% or higher. Where you belong in that range depends on how flexible your spending is and how much guaranteed income you have.

Does an 80% success rate mean a 20% chance of going broke?

Not really. It means 20% of simulated futures ran short of money at some point if spending never changed. Real retirees usually adjust when markets fall, which is why some planners call it a 'probability of adjustment' instead of a probability of failure.

Is a 100% Monte Carlo success rate the goal?

No. A score near 100% can mean you're spending too little and holding back money you could safely use. A common advisor guardrail practice treats a score near 99% as a cue to consider raising spending.

Why do different retirement calculators give different success rates?

Each tool assumes different returns, volatility, inflation, planning horizons, and costs such as health care. The model type matters as well. An Income Lab analysis found traditional Monte Carlo models had the most error compared with real outcomes. Scores from different tools aren't directly comparable.

What should I do if my Monte Carlo success rate is below 70%?

Most advisors consider that too low for a typical retiree. Test the main levers one at a time, such as spending less, working longer, or changing when you claim Social Security, and see how much each one moves the score. This is general information, not personal advice.