FIRE number calculator, the pot, the time and Coast FIRE.

Your FIRE number is the size of the pot that could pay for your spending, under the withdrawal rate you choose. FIRE stands for financial independence, retire early. This FIRE number calculator divides your yearly spending by a withdrawal rate to get the pot, then works out how long your savings take to get there and what your Coast FIRE number is. The 4 percent withdrawal rate, which makes the pot 25 times your yearly spending, is a popular rule of thumb. It is not an official figure and no rate is promised to last. The return in the box is an example, not a forecast.

How to use it

1. Type your Yearly spending in retirement and the Withdrawal rate (%). The FIRE number appears at once.
2. Type your Savings and investments now, what You add each year and a Yearly return after inflation (%). Using a return after inflation keeps the answer at today’s prices.
3. Type Your age now and Retire by age to see the Coast FIRE number.
4. If a pension or part-time pay will cover some of your spending, type it as Other income in retirement a year. If you type your income after tax, the page also shows your savings rate.
5. Read the cards, the chart and the table of other withdrawal rates. Copy result copies a line and Copy link to these numbers reopens the page with your inputs.

The FIRE number

FIRE number = yearly spending / withdrawal rate. Spending of 40,000 at 4 percent needs 1,000,000, which is 25 times 40,000. At 3.5 percent it needs about 1,142,857, and at 5 percent 800,000. A lower withdrawal rate gives a bigger pot and a bigger margin. Spending of 60,000 at 4 percent needs 1,500,000. Because the pot scales with spending, every 1,000 you cut from yearly spending lowers the FIRE number by 25,000 at 4 percent.

The last column uses the example inputs: 100,000 saved, 20,000 added a year at a 5 percent return after inflation, deposits at the end of each year.

How long it takes

The balance after n years is 100,000 x 1.05ⁿ + 20,000 x (1.05ⁿ − 1) / 0.05. Setting that to 1,000,000 gives n = 21.10 years, which the page shows as 21 years 2 months. A person of 30 would be about 51 at that point. Add more each year or earn a higher return and the time shrinks, and the chart shows it. Return is the part nobody knows ahead of time, so try several values.

When other income pays part of the bill

The pot only has to cover what other income does not. With spending of 40,000 and 10,000 a year from a pension or part-time work, the pot must pay 30,000. At 4 percent that is 750,000 instead of 1,000,000, and the example savings reach it in about 17 years 1 month instead of 21 years 2 months. The 10,000 should be at today’s prices, like everything else on the page. If the other income is not certain, test the case without it too.

Spending a little less or more

Lean, regular and fat FIRE are labels without one agreed definition, so the page does not claim any. Instead, a table shows your spending at 60, 80, 100, 120 and 150 percent. With the example at 4 percent, spending of 24,000 needs 600,000 (14 years 3 months), 32,000 needs 800,000 (17 years 11 months), 48,000 needs 1,200,000 (23 years 10 months) and 60,000 needs 1,500,000 (27 years 4 months).

Coast FIRE

Coast FIRE is the amount that, if you stopped adding to it now, would grow by itself to your FIRE number by the age you pick. It is the FIRE number divided by (1 + return) for each year left. With 35 years from age 30 to 65 at 5 percent, 1,000,000 / 1.05³⁵ = 181,290.29. The example saver has 100,000, below that, so they have not passed it. Left alone, 100,000 would take 47.19 years to reach 1,000,000. Once you pass the coast number you only need to cover your living costs until the age you pick, and the savings can grow on their own. Treat it as a way to think about the plan, not a promise.

What moves the answer

Three inputs move the time to FIRE: spending, saving and the return. Starting from the example, which takes 21.10 years:

Spending has the biggest pull because it shrinks the target and, in real life, leaves more to save. A change of one point in the return moves the time by about two years in either direction, which is why a plan is better tested with a low return as well as a hopeful one.

What the page leaves out

• Tax on withdrawals, fees, and the way the order of good and bad years changes what a pot can pay.
• Pensions, social benefits and part-time income, which lower what the pot has to cover.
• Spending that changes. Health costs and one-off costs can move the number.
• No withdrawal rate is guaranteed to last. The 4 percent idea comes from studies of past market data and is a starting point to test, not a rule.

To see a balance grow with deposits and a goal, use the investment calculator. For retirement account contributions there is the 401k calculator. To see what savings buy later, try the inflation calculator.