Retirement Calculator and Planner: From Odds to Action

3.9%. Morningstar found that this starting withdrawal rate held up in 90% of simulated futures over a 30-year retirement. Look at how it was judged. Morningstar didn't use an average return. It asked whether the money was still there at the end. Your own plan should be tested the same way. A good retirement calculator and planner takes your age, savings and spending, gives you back the probability that your money lasts, and then helps you decide what to change.

Source: Morningstar, The State of Retirement Income 2025, December 2025.

This guide covers how that kind of answer is produced, what a "success rate" means, and how to go from a percentage to an action plan.

Why most retirement calculators give you the wrong kind of answer

Most retirement calculators online, often from banks, credit unions and insurers, ask for the same inputs: current age, retirement age, savings, contributions and an expected rate of return. They give you a future balance, the monthly savings you need, and a shortfall or surplus.

That's a reasonable place to start. But nearly all of them assume one return, every year, in a straight line.

Markets don't behave that way. Two retirees can get the same average return and still end up in very different places, because the order of returns matters. A few bad years right after you start withdrawing do more damage than the same bad years a decade later. You're selling into the dip and have less left to recover with. A calculator that follows one path can't show you that.

There's a second problem: big headline targets. In Northwestern Mutual's 2026 study, Americans said they need about $1.46 million to retire comfortably. In Schroders' 2026 survey, workplace plan participants said $1.2 million. Those figures are what people believe they need. They aren't your number. Your number depends on what you actually spend.

Plenty of people haven't worked that out yet. The EBRI/Greenwald Retirement Confidence Survey 2025 found that only 52% of workers have estimated the monthly income they'll need in retirement. The other 48% are guessing.

Sources: Northwestern Mutual, Planning & Progress Study 2026; Schroders, 2026 U.S. Retirement Survey; EBRI/Greenwald Retirement Confidence Survey 2025, Fact Sheet 3.

How a Monte Carlo retirement planner works, in plain English

"Monte Carlo" sounds technical, but the idea is simple. Instead of running your plan once with one assumed return, you run it many times. Each run uses a different sequence of market years, randomized within realistic ranges.

Here's what happens:

1. Start with your numbers. Age, savings and monthly spending.
2. Simulate a future. Each year gets a market return, good, bad or flat, and the plan takes out your spending.
3. Check the ending. Did the money last to the end of the plan, or did it run out?
4. Repeat. Do this 1,000 times.
5. Count. The share of futures that stayed funded is your success rate.

So if 850 of 1,000 simulated futures stay funded, your success rate is 85%. (That's an illustration, not a benchmark.) The calculator isn't telling you what will happen. It's showing how often your plan survives across a wide range of things that could happen.

What your success rate means, and what it doesn't

A success rate is a probability, not a promise. Keep that in mind as you read it.

There's no universal "right" number. Morningstar uses 90% as the bar in its safe-withdrawal research. That's a cautious standard, not a law. Some people are fine with a lower figure because they know they can cut spending if markets go badly. Others want more margin. CNN Money's explainer on Monte Carlo success rates makes the same point: the percentage only means something next to how flexible you are.

Failure isn't all-or-nothing. Retirement researcher David Blanchett points out that a plan which meets its goal every year until the last one, then comes up a dollar short, still counts as a "failure" in a standard Monte Carlo test. A plan that runs dry at 78 is a very different problem from one that falls a little short at 94. NAPA's interview with Blanchett covers this well.

So when you look at your result, ask three questions:

• How often does the plan fail?
• When does it fail? Early, or late in life?
• By how much? A small shortfall you could cover by trimming spending, or a deep hole?

Larry Swedroe covers this in What If Your Plan Fails?. The useful question isn't only "will it work?" It's also "what would I do if it started to go wrong?"

Results depend on assumptions. Small changes in expected returns or volatility can move a success rate noticeably. A trustworthy planner makes its assumptions visible, and you should rerun the plan whenever your situation changes.

The three risks a retirement calculator and planner must include

A simulation is only as honest as its inputs. These three are the ones that most often get skipped.

1. Living longer than you planned

The Social Security Administration estimates that about one in three 65-year-olds may live to at least 90. A plan that ends at 85 is quietly betting against a third of retirees. Running to 95 by default is the more careful choice.

Source: Social Security Administration, Retirement Information for Medicare Beneficiaries, 2026.

2. Health care costs

Fidelity estimates that one 65-year-old retiring in 2025 will need $172,500 for Medicare premiums, deductibles and prescriptions over retirement. That figure doesn't include long-term care. It's a real line item in your budget, and a planner should charge those costs year by year instead of folding them into a vague "expenses" number.

Source: Fidelity Investments, 2025 Retiree Health Care Cost Estimate, July 2025.

3. Your withdrawal rate

Your withdrawal rate is the share of your portfolio you take out in the first year of retirement. Morningstar's 3.9% figure gives you a rough check. With $800,000 saved, a 3.9% starting withdrawal is $31,200 a year, about $2,600 a month. If you plan to spend much more than that, your success rate will show it.

That's arithmetic, not a recommendation. Your Social Security, pension, other income and timeline all change the picture.

From success rate to action plan

The number is where you start. These are the levers that move it:

Change one lever at a time and rerun. You'll quickly see which changes make a real difference to your plan and which barely register.

If you're still working: 2026 contribution limits

If saving more is one of your levers, here are the IRS limits for 2026:

The ages 60–63 window matters most if you're close to retiring. It's the largest catch-up available, and it only lasts a few years. One more rule: if you earned more than $150,000 in 2025, your catch-up contributions must go in as Roth (after-tax) money. Check how that applies to your plan on the IRS catch-up contributions page.

Source: IRS, COLA Increases for Dollar Limitations on Benefits and Contributions.

Rerun after every real change

A new job, a market drop, an unexpected expense, a change in health. Each one changes your inputs. A success rate from two years ago is answering an old question.

Running your own numbers with Monte Climb

This is the gap we built Monte Climb's retirement calculator to fill. You enter three numbers: your age, what you've saved for retirement and what you spend each month. We run them through 1,000 simulated futures, using the same engine behind the app, and show your success rate: how many of those futures stay funded.

It runs in your browser. Nothing is saved until you say so.

From there you can ask William, our AI planner, the follow-up questions: Am I on track? Can I retire at 62? What's a sustainable spend? You can talk to him like you would a friend.

The plan you build in the app runs to age 95 by default, and you can push it further. It charges Medicare premiums and income-based surcharges year by year instead of using a flat guess. You can try it for $1 for 7 days.

One reminder: this is planning software, not advice. It shows you the odds. The decisions are yours.

Three numbers. One clear answer. Show my answer →

Frequently asked questions

What is a good success rate for a retirement plan?

There's no universal target. Morningstar uses 90% as the bar in its safe-withdrawal research, which is a cautious standard. Some people are comfortable lower because they can cut spending if markets go badly. Whatever your percentage, also look at when and by how much the failing scenarios fall short.

How is a Monte Carlo retirement calculator different from a regular one?

Most retirement calculators assume one average return every year. A Monte Carlo calculator runs your plan many times, for example across 1,000 simulated futures with different market sequences, and reports the share that stay funded. That captures the risk of bad markets early in retirement, which a single straight-line projection can't show.

What age should my retirement plan run to?

The Social Security Administration estimates about one in three 65-year-olds may live to at least 90, so a plan that ends at 85 underestimates longevity risk. Running your plan to 95 or later is the more careful choice.

How much can I safely withdraw from my retirement savings?

Morningstar's 2025 research puts the safe starting withdrawal rate at 3.9% for a 30-year retirement, based on the money lasting in 90% of simulated outcomes. That's a useful starting point, not a personal recommendation. Your income sources, timeline and flexibility all change the answer.

Is an online retirement calculator the same as financial advice?

No. A retirement calculator and planner shows you probabilities based on the numbers you enter. It's planning software, not personalized financial advice. It's a way to understand your odds and test changes before you decide.