How it's calculated
FIRE number = annual spending / withdrawal rate (4% → 25 × spending)
Years to FI = first month where B ≥ FIRE number, with B = B·g + (annual savings / 12)
g = (1 + real return)^(1/12)
Coast FIRE today = FIRE number / (1 + real return)^(coast age − current age)
- The withdrawal rate is an assumption. The "4% rule" comes from research on historical US stock and bond returns (William Bengen in 1994, and later the "Trinity study"), which looked at withdrawing 4% of a portfolio in the first year and raising it with inflation over roughly 30 years. It is not a guarantee. Retirements longer than 30 years, different investments, fees and taxes, or bad early returns can change the outcome. This calculator simply divides your spending by the rate you enter.
- Today's dollars. Using a real (after-inflation) return keeps spending, savings and the FIRE number in today's buying power, so no separate inflation input is needed.
- Coast FIRE is the amount that, with no further contributions, would grow to your FIRE number by your coast age at the same real return.
- Not modeled: taxes, Social Security or pensions, health insurance, changing spending, variable returns. Savings are invested monthly at the end of each month, and the return is the same every year.
Worked examples
1. $40,000 a year at 4%
FIRE number = 40,000 ÷ 0.04 = $1,000,000.00. Starting with $50,000.00 and investing $24,000.00 a year at a 5% real return, you would reach it in 20 years and 10 months, around age 50. Load this example
2. A more cautious 3.5% withdrawal rate
40,000 ÷ 0.035 = $1,142,857.14 (about 28.6× spending), which takes 22 years and 8 months with the same savings. Load this example
3. Coast FIRE
If you're 30 and would be happy to stop contributing and simply let the money grow until 65, you'd need 1,000,000 ÷ 1.0535 = $181,290.29 invested today (at a 5% real return). After that, your job only has to cover current expenses. Load this example
Frequently asked questions
How do I calculate my FIRE number?
Divide the yearly amount you expect to spend in retirement by your withdrawal rate. At 4% that is 25 times your annual spending: $40,000 a year needs $1,000,000; $60,000 needs $1,500,000.
Is the 4% rule safe?
It is a rule of thumb based on historical US returns over roughly 30-year retirements, not a promise. Early retirees may need their money to last 40–50 years, which is why many test lower rates like 3.25–3.5%. This calculator lets you change the rate and see the effect.
What is Coast FIRE?
Coast FIRE means you have enough invested that, even if you never contribute again, growth alone should reach your FIRE number by a normal retirement age. You still need income to cover current expenses, but not to save for retirement.
Does this FIRE calculator include inflation?
Yes, by using a real (after-inflation) return. All amounts, including your spending and FIRE number, are in today's dollars.
What about Social Security or a pension?
They aren't modeled, because they usually start years after an early retirement and depend on your work history. Some people reduce the spending figure by expected benefits, but that only works once those benefits begin.