How to use the FIRE calculator

Enter your age and the spending you expect in retirement, in today’s money. Most people start from their current budget and adjust for the mortgage ending or travel starting.
Choose a safe withdrawal rate. 4% is the traditional figure; 3% or 3.5% is the cautious choice for a retirement longer than 30 years.
Add what you have invested today and what you invest each year. Include employer contributions if they land in an account you can eventually draw on.
Set a real return. 5% after inflation is a common planning assumption for a diversified stock-heavy portfolio; use less if you hold a lot of bonds or cash.
Read the results. You get your FIRE number, the year you cross it, the Coast FIRE amount for your target retirement age, and Lean and Fat variants. The table and chart below break the path down year by year.

How the maths works

The FIRE number comes straight from the withdrawal rate:

FIRE number = annual spending ÷ (withdrawal rate ÷ 100)

A 4% rate is the same as 25× spending, 3.5% is about 28.6×, and 3% is 33.3×. The multiple is simply 100 ÷ rate.

The projection then grows your portfolio one year at a time, using a real return so every number stays in today’s money:

end of year = start × (1 + real return) + annual contribution

Contributions land at the end of each year, which is the conservative choice; investing monthly through the year gives a slightly earlier finish. The loop stops as soon as the balance reaches the FIRE number, or after 100 years, in which case the tool tells you the target is out of reach with those inputs.

Coast FIRE runs the same compounding backwards from your target retirement age:

Coast FIRE = FIRE number ÷ (1 + real return) ^ years until retirement

Variant	Spending used	At 4%, from $40,000
Lean FIRE	70%	$700,000
Standard FIRE	100%	$1,000,000
Fat FIRE	150%	$1,500,000

Where the 4% rule comes from

The figure traces back to William Bengen’s 1994 study and to the 1998 Trinity study by three Trinity University professors. Both looked at historical US market data and asked a narrow question: what starting withdrawal, increased each year with inflation, would have survived a 30-year retirement in every historical window? The answer for a portfolio of roughly half stocks and half bonds was close to 4%.

Three details are worth keeping in mind, and none of them makes the rule useless:

It was a 30-year test. Someone retiring at 40 may need 50 years of income, which lowers the sustainable rate.
It is US data from a strong century. Studies covering other developed markets generally find lower safe rates.
It is a rule about starting withdrawals. In practice most retirees adjust spending when markets fall, which meaningfully improves the odds.

Sequence-of-returns risk is the reason a single average return is not the whole story. Two retirees can experience the same average return over 30 years and get opposite outcomes, because the one who meets a deep bear market in the first few years sells more shares at low prices to fund the same spending, permanently shrinking the portfolio. That is why this calculator’s year count is a planning estimate rather than a promise, and why many people keep a cash buffer, stay flexible about spending, or work a little longer than the model suggests. Nothing here is financial advice.

Worked examples

The classic case. Spending of $40,000 a year at a 4% withdrawal rate gives a FIRE number of $40,000 ÷ 0.04 = $1,000,000.

A saver at 30. Age 30, $50,000 invested, $20,000 added per year, 5% real return, $40,000 of spending. The portfolio passes $1,000,000 during year 24, ending around $1,051,000 — financial independence at about age 54.

Coasting instead. That same 30-year-old, targeting retirement at 65, needs $1,000,000 ÷ 1.05^35 ≈ $181,300 invested today to coast. With $50,000 already invested they are not there yet, but at 40 the Coast FIRE bar for a 65-year-old retirement is $1,000,000 ÷ 1.05^25 ≈ $295,300.

Trimming the budget. Drop spending to $28,000 — Lean FIRE — and the target falls to $700,000, which the same saver reaches in year 19 instead of 24. Spending assumptions move the finish line far more than return assumptions do.

Tips

Model spending, not income. Your FIRE number depends on what you spend, so a careful budget is worth more than a clever return forecast.
Remember taxes and health cover. Withdrawals may be taxed, and in some countries insurance is a large line item before state pension age. Put them in the spending figure.
Do not forget other income. A state pension, rental income or part-time work reduces the portfolio you need; subtract it from annual spending before you calculate.
Re-run it once a year. Savings rates, spending and markets all move. The tool keeps your inputs in your browser so an annual check takes a minute.

Glossary

FIRE number – the invested amount that supports your spending at your chosen withdrawal rate.
Safe withdrawal rate (SWR) – the percentage of the starting portfolio withdrawn in the first year, then adjusted for inflation.
Real return – investment return after inflation.
Coast FIRE – the point where existing investments alone will grow into your FIRE number by your target age.
Sequence-of-returns risk – the risk that poor returns early in retirement do lasting damage, even if long-run averages are fine.

Frequently asked questions

How do I calculate my FIRE number?

Divide your expected annual spending in retirement by your withdrawal rate. At a 4% rate, $40,000 of spending needs $40,000 ÷ 0.04 = $1,000,000, which is the same as 25 times your annual spending.

Is the 4% rule still valid?

It is a useful starting point, not a guarantee. The original Trinity study tested US portfolios over 30-year windows from 1926 to 1995 and found a 4% initial withdrawal, adjusted for inflation, survived almost every window. Later work using lower expected returns, longer retirements or non-US data often suggests 3% to 3.5% instead.

What is Coast FIRE?

Coast FIRE is the amount that, left invested with no further contributions, would grow into your full FIRE number by your chosen retirement age. Once you pass it you still need income for today's bills, but you no longer have to save for retirement.

What is the difference between Lean and Fat FIRE?

They are informal labels for different spending levels. This calculator shows Lean FIRE at 70% of your stated spending and Fat FIRE at 150%, so you can see how sensitive the target is to your budget.

Should I use a real or nominal rate of return?

Use a real, inflation-adjusted return, which is what this tool expects. Then every figure it shows is in today's money and you do not have to inflate your future expenses separately.

Why do the yearly figures assume the same return every year?

A constant return keeps the model transparent. Real markets swing, so treat the year count as a central estimate rather than a date in your diary, and revisit it as your savings and spending change.

Related tools

Last reviewed: September 21, 2026

Year	Age	Start balance	Invested	Growth	End balance
1	31	$50,000	$20,000	$2,500	$72,500
2	32	$72,500	$20,000	$3,625	$96,125
3	33	$96,125	$20,000	$4,806	$120,931
4	34	$120,931	$20,000	$6,047	$146,978
5	35	$146,978	$20,000	$7,349	$174,327
6	36	$174,327	$20,000	$8,716	$203,043
7	37	$203,043	$20,000	$10,152	$233,195
8	38	$233,195	$20,000	$11,660	$264,855
9	39	$264,855	$20,000	$13,243	$298,098
10	40	$298,098	$20,000	$14,905	$333,003
11	41	$333,003	$20,000	$16,650	$369,653
12	42	$369,653	$20,000	$18,483	$408,135

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