Coast FIRE Calculator
"Coast FIRE" is the amount you'd need invested today so that, left alone to compound, it would grow to your retirement target by your target age with no further contributions. This is an educational estimate, not financial advice — actual returns vary.
How the number is worked out
This is a present-value calculation. It runs compounding backwards from the target you want at retirement to the balance that would get there on its own:
Coast FIRE number = target / (1 + return)^yearsWith the defaults - a $1,000,000 target, 30 years to go and 7% a year - 1.07^30 is 7.6123, so you need 1000000 / 7.6123 = $131,367 invested today. Wait ten years and the sum is 1000000 / 1.07^20 = $258,419, because the money has a decade less to work. At 5% instead of 7% over the same 30 years it is $231,377.
Reading the result honestly
- Match the return to the target. A 7% nominal return has to be paired with a nominal target - roughly what $1,000,000 of today's spending will cost in 30 years. Prefer to think in today's money? Enter a real return, around 4% to 5%, and read the target as today's dollars.
- One average, not a path. The tool applies the same return every year. For a lump sum with no contributions and no withdrawals the order of returns genuinely does not matter, only the total compounding - but the total itself is unknown, and 30 years of 7% is an assumption, not a fact.
- Edge cases. Zero years returns the target unchanged, and a 0% return does the same. The target must be above zero.
Frequently asked questions
What is Coast FIRE?
The point where your existing investments, left completely alone, would grow into your retirement target by the age you picked. You keep working to cover current spending, but you no longer have to add to the pot.
How much do I need to coast to $1 million in 30 years?
About $131,367 at a 7% annual return. At 5% it is $231,377, and with only 20 years left at 7% it is $258,419.
Why is my Coast FIRE number so sensitive to the return I type?
Because the return is raised to the power of the years. Over 30 years, moving from 7% to 6% raises the amount you need today by about a third.