What is a FIRE number?
Your FIRE number is how much you need invested on the day you stop working so your savings can pay for the rest of your life. Without a pension or Social Security, it's your yearly spending divided by your withdrawal rate. At the common 4% rate, that's 25 times what you spend in a year.
How the calculator works
Enter what you expect to spend in a year once you stop working, in today's dollars, and the share of your savings you plan to take out in the first year of retirement. That second number is your withdrawal rate. The calculator turns the two into the amount you need invested on day one.
The basic formula
FIRE number = yearly spending ÷ withdrawal rateAt 4% that's 25 times your spending. At 3.5% it's about 28.6 times, and at 3% about 33.3 times.
The 4% figure comes from the Trinity study and later research like it. Those studies asked how much retirees could have taken from a stock and bond portfolio, raising the amount with inflation every year, without running out over 30 years. So 4% is a rule about 30-year retirements. If you stop work at 45, your money may have to last 50 years, and a lower rate leaves more room for bad markets. That's why the table under your result also shows 3.5% and 3%.
When you have Social Security or a pension
Income that pays part of your bills lowers your number, but the calculator doesn't just subtract it. It works out the gap your savings have to fill in each year of retirement, then adds those gaps up, using a discount rate tied to your withdrawal rate. Income that starts several years after you retire still helps. It helps less, because your savings carry the whole bill until the first check arrives. How we calculate has the full method.
Taxes on withdrawals
FIRE number = yearly spending ÷ (1 − tax rate) ÷ withdrawal rateMoney in a 401(k) or traditional IRA is taxed when it comes out. If 15% of each withdrawal goes to tax, you have to withdraw more to end up with the same spending money.
Leave the tax rate at 0 if most of your savings are in Roth accounts, or if the spending you entered already includes your tax bill. Don't count tax twice.
Three worked examples
Example 1: the 25-times rule
Someone expects to spend $60,000 a year once they stop working and uses a 4% withdrawal rate. They have no pension and haven't counted Social Security.
| Spending per year | $60,000 |
|---|---|
| Withdrawal rate | 4% |
| FIRE number | $1,500,000 |
|---|
Divide $60,000 by 4% and you get $1,500,000, which is 25 times their yearly spending. Withdrawing 4% of that in the first year gives back exactly the $60,000 they need.
Example 2: adding Social Security
The same person plans to retire at 60 and expects $24,000 a year of Social Security, after tax and in today's dollars, starting at 67.
| Spending per year | $60,000 |
|---|---|
| Retire at | 60 |
| Social Security | $24,000 a year from 67 |
| Withdrawal rate | 4% |
| FIRE number | $1,057,252 |
|---|---|
| Without Social Security | $1,500,000 |
From 67 on, Social Security pays $24,000 of the $60,000, so savings only cover the rest. For the seven years from 60 to 66 there's no check yet, and savings pay the full $60,000. That's why the number drops to $1,057,252 and not further: the early years still need the full amount.
Example 3: taxes on withdrawals
Another person wants $50,000 a year to spend. Almost all of their savings are in a traditional 401(k), and they expect about 15% of each withdrawal to go to tax.
| Spending per year | $50,000 |
|---|---|
| Tax on withdrawals | 15% |
| Withdrawal rate | 4% |
| Withdrawn per year before tax | $58,824 |
|---|---|
| FIRE number | $1,470,588 |
| Without the tax | $1,250,000 |
To keep $50,000 after a 15% tax, they have to withdraw about $58,824 a year. At 4%, that takes $1,470,588 invested, against $1,250,000 if the money came out tax-free.
What moves your FIRE number most
Spending is the biggest lever by far. At 4%, every $1,000 you add to your yearly budget adds $25,000 to your FIRE number, and every $1,000 you cut takes $25,000 off. Cutting a $500 monthly expense you don't care about is worth $150,000 of savings you no longer need.
The withdrawal rate comes next. Going from 4% to 3.5% raises the number by about 14%: the same $60,000 a year needs $1,714,286 instead of $1,500,000. It's a real cost, but for retirements longer than 30 years it buys a lot of safety.
Income in retirement matters more the sooner it starts. A pension that begins the year you retire cuts your number almost dollar for dollar against your spending. Social Security that starts ten years later still helps, just by less.
If the number looks out of reach, there are two in-between paths. With Coast FIRE, you stop saving once your investments can grow into your FIRE number on their own, and keep working only to cover your bills. With Barista FIRE, part-time income covers some of your spending, so you need less saved before you leave full-time work. The Barista FIRE calculator works that out.
Why FIRE number calculators give different answers
Put the same spending into five calculators and you can get five different numbers. The math is simple, so the differences come from the assumptions:
- The withdrawal rate. Most default to 4%, some to 3.5% or 3.25% for early retirees. A half-point difference changes the answer by about 14%.
- Today's dollars or future dollars. This calculator shows what you need in today's money. Some tools grow your spending by inflation until the year you retire and show that bigger future amount. Both can be right. They just answer different questions.
- How income is counted. Some tools subtract Social Security from your spending as if it started the day you retire. If it actually starts years later, that understates what you need.
- Taxes. Many calculators ignore them, which works for Roth savings and understates the number for traditional 401(k) and IRA money.
When you compare tools, set them to the same withdrawal rate and the same kind of dollars first. Most of the gap usually disappears.
What this calculator doesn't do
- It assumes your spending stays the same in real terms for the rest of your life. Many retirees spend more in their 60s and less in their 80s, with health costs rising late.
- It uses one flat tax rate on withdrawals. Real taxes depend on which accounts you draw from, your other income, and where you live.
- Your plan runs to 95. If your family tends to live longer, a lower withdrawal rate gives you more room.
- It doesn't show what happens if markets fall in your first few years of retirement, which is the biggest risk to any withdrawal rate. A lower rate, or spending you can trim in bad years, is the usual protection.
- It doesn't tell you when you'll get there. That depends on what you have now and what you save, which the Coast FIRE calculator takes into account.
Common questions
What is a FIRE number?
It's the amount you need invested to stop working for good, with your savings paying for whatever your other income doesn't. Most people work it out as 25 times their yearly spending, which is the same as dividing spending by a 4% withdrawal rate.
How do I calculate my FIRE number?
Take what you expect to spend in a year in retirement and divide it by your withdrawal rate. For $60,000 at 4%, that's $1,500,000. If you'll have a pension or Social Security, enter it above. The calculator accounts for when it starts, which simple subtraction gets wrong.
Should I use 4% or 3.5%?
4% held up over 30-year periods in past US markets. If you plan to retire before about 55, your money may need to last 40 or 50 years, and many planners use 3.5% or lower for that. The table under your result shows both, so you can see what the extra safety costs.
Does my FIRE number include Social Security?
Only if you add it. Click Social Security or a pension, enter the yearly amount after tax and the age it starts, and the age you plan to retire. Your number will drop, by more the earlier the income starts.
Is my FIRE number in today's dollars?
Yes. Everything here is in today's money, and the calculation assumes your investments and your spending both keep up with inflation. In 25 years the same lifestyle will cost more dollars, but you'll be comparing it against savings that grew too.
What is a good FIRE number?
There isn't a universal one, because it depends entirely on what you spend. A household spending $40,000 a year needs about $1,000,000 at 4%. One spending $100,000 needs $2,500,000. The Lean FIRE and Fat FIRE calculators start from budgets at each end.
How long will it take to reach my FIRE number?
That depends on what you have invested, how much you save, and the return you get. The Coast FIRE calculator follows your savings year by year and shows the age you could stop saving and the age you'd reach your full number.
Sources
- Cooley, Philip L., Carl M. Hubbard and Daniel T. Walz. "Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable." AAII Journal, February 1998. Usually called the Trinity study.
- Jeske, Karsten (Early Retirement Now). The Safe Withdrawal Rate Series. earlyretirementnow.com/safe-withdrawal-rate-series
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