How does the Retirement Fund Calculator work?

You enter your age, what you have saved, what you put away each month, what you expect to spend in retirement and any pension that will pay part of it. The calculator grows your savings year by year to the age you want to stop work, then draws your spending from them until the age you plan to. It does that once on a steady line, which gives the freedom number, and then a thousand times through markets that rise and fall, which gives the fan on the chart and the chance that the money lasts.

What is the freedom number, and why is there a second one?

The freedom number is what you need on the day you retire for the money to run out exactly at the age you plan to, if markets grow at the steady rate you entered. It is the middle of the road, so hitting it exactly leaves about half of the simulated markets running dry early. The second figure, the 90% number, is the amount that lasts in nine markets out of ten. It is usually well above the freedom number, and the gap between them is the price of not knowing which markets you will get.

What does the chance that the money lasts mean?

The calculator runs your plan through a thousand simulated markets. Each year's growth is drawn at random around the rate you entered, spread by the volatility you set, so some runs start retirement in a slump and some in a boom. The chance is the share of those runs in which your savings still cover your spending at the age you plan to. The draws are fixed, so moving a slider changes your plan, not the dice. It is a way to see how much the order of good and bad years matters, not a forecast.

What is the difference between fixed spending and guardrails?

Fixed spending takes the same amount in today's money every year, whatever markets do, which is how the 4% rule studies by William Bengen and the Trinity professors tested it. Guardrails, from Jonathan Guyton and William Klinger's 2006 paper, let spending move. If a fall in the markets pushes this year's withdrawal more than 20% above the rate you started at, spending is cut by 10%. If a rise pulls it 20% below, spending goes up by 10%. Cuts stop in the last fifteen years. The calculator shows how low spending falls in a bad run, so you can judge whether you could live with it.

Why is everything in today's money?

So that a number at 80 means what it would buy now. Returns are turned into growth above inflation, and your spending and saving stay level in today's terms, which means you raise your saving with prices each year. The freedom number is also shown in the money of the year you retire, which is the figure a bank statement would show then.

What does it leave out?

Taxes, investment fees, a home you might sell, care costs late in life, one-off costs such as a new roof, inflation that changes from year to year, and the rules of any particular pension or account. Returns are drawn from a simple random model, not replayed from history. Treat the results as a way to see which of your choices matter most, then check the plan with someone qualified where you live. Nothing here is financial advice.

Where is my plan saved, and what does a share link contain?

Your scenarios and settings are saved in this browser after every change, so a reload keeps them. If you are signed in, they are also saved to your HourLife account, so they open on your other devices, and you can delete them there in Settings. Signed out, nothing is sent to HourLife or anyone else. A share link carries the numbers of the scenario you are looking at after the

Which currencies does it use?

Dollars, euros, pounds, Swiss francs and a few more. The currency only changes the symbol and the number format. Every amount is yours to enter, and the results scale with what you type, so use the currency you spend in.

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Retirement Fund Calculator

Will the money last as long as you do?

Open the planner Start from an example

Enter what you have, what you save and what you will spend. The calculator runs your plan through a thousand markets, good and bad, and shows the chance it lasts, the number to aim for, and which change would close the gap. Try up to four plans side by side.

1,000 markets per plan
4 plans side by side
Free, no account

How it works

The chart above, taken apart. Thirteen numbers on a rail, the answer redrawn as you move them. Every amount is in today's money, so a figure at 80 means what it would buy now.

Describe the plan

Your age, what you have saved and put away each month, the age you want to stop work, what you will spend each month after that, and any pension that pays part of it from the age it starts.

$0$500K$1M$872,025 at 65Put away $1,500 a monthSpend $5,500 a monthRuns out at 86
Run it through a thousand markets

Each year's growth is drawn at random around the rate you enter, spread by the volatility you set. Some runs retire into a slump, some into a boom. The chart fans out to show the spread, with the middle run drawn through it.

$0$1M$2M40 of the 1,000 marketsThe middle market
See what would close the gap

If fewer than nine markets in ten last, the planner solves three levers on their own: how much later to stop, how much more to save, or how much less to spend. If the plan is on track, the same levers show how much room you have.
0%50%100%90% line37% still funded at 92
- Stop work at 7510 years later
- Save $4,450 a month$2,950 more until 65
- Spend $3,370 a month$2,130 less in retirement

Two numbers, not one

Most retirement calculators give you a single target. That target is the middle of the road, and the middle of the road runs dry early in about half of markets.

The freedom number

If markets grow at the steady rate

What you need on the day you stop work for the money to run out exactly at the age you plan to, if every year grows at the rate you entered. It is the figure to compare with what you are on course to have.

The 90% number

If markets are what they usually are

The smallest amount on retirement day that lasts in nine markets out of ten. The gap between the two is the price of not knowing which order the good and bad years will come in, which matters most in the first years after you stop.

In the sample above the freedom number is about a million and the 90% number about 1.6 million. The same plan, the same averages; the difference is only the order of the years.

Fixed spending or guardrails

How you spend in a bad market changes how much you need. Here is the same plan, the same thousand markets, under each rule. The planner runs either, and the compare table puts them side by side.

Fixed

$0$500K$1M$1.5MA bad market
runs out at 76

Lasts to 92: 37% of markets
In a bad market: Runs out at 76
90% number: $1,630,159
Spending in a bad market: $5,500 a month, every year

Guardrails

$0$500K$1M$1.5MA bad market
lasts to 92

Lasts to 92: 91% of markets
In a bad market: Lasts to 92
90% number: $785,769
Spending in a bad market: Falls to $2,368 a month at its lowest

The 4% rule studies

The same spending every year, whatever markets do. It is how William Bengen and the Trinity study tested withdrawals, and it is the safe choice to plan with if your spending cannot bend.

Guyton and Klinger, 2006

If a fall pushes this year's withdrawal more than 20% above the rate you started at, spending drops by 10%; if a rise pulls it 20% below, spending goes up by 10%. Cuts stop in the last fifteen years. The planner shows how low spending gets in a bad market, so you can judge whether you could live on it.

What it leaves out

A way to see which of your choices matter most, not financial advice. Check the plan with someone qualified where you live before you act on it.

Taxes and fees. Enter spending and returns after them, or treat the results as before both.
Your home. A house you might sell or downsize is not counted as savings.
Late-life costs. Care and one-off bills, such as a new roof, are not modelled.
Changing inflation. Prices rise at one steady rate, every year.
Real market history. Years are drawn from a simple random model, not replayed from the past.
Account rules. No pension or tax-advantaged account's rules are applied.

What it is built on

The research behind the numbers, stated no more strongly than the studies do.

The 4% rule William P. Bengen, Journal of Financial Planning, October 1994
Looking back over US market history, a first-year withdrawal of 4%, raised with inflation each year after, lasted at least thirty years in every period he tested, including the worst, which began in 1966.
The chance that it lasts Cooley, Hubbard and Walz, AAII Journal 20(2), February 1998
The Trinity study reported withdrawals as a success rate across historical periods rather than a single yes or no, which is the idea behind the planner's chance figure.
Guardrails Jonathan Guyton and William Klinger, Journal of Financial Planning, March 2006
Cutting spending by 10% when the withdrawal rate drifted 20% above where it started, and raising it the same way, supported first-year withdrawals of 5.2–5.6% at a 99% success rate for portfolios with at least 65% in stocks.
Today's starting rate Morningstar, The State of Retirement Income, 2025
Using forward-looking estimates of returns rather than history, Morningstar put a safe fixed starting withdrawal at 3.9% for thirty years at a 90% success rate, up from 3.7% earlier the same year. Starting rates move with market valuations.

Start from a plan like yours

Each example opens as its own scenario beside any plans you already have in this browser. Change any number to make it yours.

Questions

How does the Retirement Fund Calculator work?

You enter your age, what you have saved, what you put away each month, what you expect to spend in retirement and any pension that will pay part of it. The calculator grows your savings year by year to the age you want to stop work, then draws your spending from them until the age you plan to. It does that once on a steady line, which gives the freedom number, and then a thousand times through markets that rise and fall, which gives the fan on the chart and the chance that the money lasts.
What is the freedom number, and why is there a second one?

The freedom number is what you need on the day you retire for the money to run out exactly at the age you plan to, if markets grow at the steady rate you entered. It is the middle of the road, so hitting it exactly leaves about half of the simulated markets running dry early. The second figure, the 90% number, is the amount that lasts in nine markets out of ten. It is usually well above the freedom number, and the gap between them is the price of not knowing which markets you will get.
What does the chance that the money lasts mean?

The calculator runs your plan through a thousand simulated markets. Each year's growth is drawn at random around the rate you entered, spread by the volatility you set, so some runs start retirement in a slump and some in a boom. The chance is the share of those runs in which your savings still cover your spending at the age you plan to. The draws are fixed, so moving a slider changes your plan, not the dice. It is a way to see how much the order of good and bad years matters, not a forecast.
What is the difference between fixed spending and guardrails?

Fixed spending takes the same amount in today's money every year, whatever markets do, which is how the 4% rule studies by William Bengen and the Trinity professors tested it. Guardrails, from Jonathan Guyton and William Klinger's 2006 paper, let spending move. If a fall in the markets pushes this year's withdrawal more than 20% above the rate you started at, spending is cut by 10%. If a rise pulls it 20% below, spending goes up by 10%. Cuts stop in the last fifteen years. The calculator shows how low spending falls in a bad run, so you can judge whether you could live with it.
Why is everything in today's money?

So that a number at 80 means what it would buy now. Returns are turned into growth above inflation, and your spending and saving stay level in today's terms, which means you raise your saving with prices each year. The freedom number is also shown in the money of the year you retire, which is the figure a bank statement would show then.
What does it leave out?

Taxes, investment fees, a home you might sell, care costs late in life, one-off costs such as a new roof, inflation that changes from year to year, and the rules of any particular pension or account. Returns are drawn from a simple random model, not replayed from history. Treat the results as a way to see which of your choices matter most, then check the plan with someone qualified where you live. Nothing here is financial advice.
Where is my plan saved, and what does a share link contain?

Your scenarios and settings are saved in this browser after every change, so a reload keeps them. If you are signed in, they are also saved to your HourLife account, so they open on your other devices, and you can delete them there in Settings. Signed out, nothing is sent to HourLife or anyone else. A share link carries the numbers of the scenario you are looking at after the
Which currencies does it use?

Dollars, euros, pounds, Swiss francs and a few more. The currency only changes the symbol and the number format. Every amount is yours to enter, and the results scale with what you type, so use the currency you spend in.