How to use the coast fire calculator
- Enter the target amount you want to have when you reach retirement.
- Enter the years until then and a yearly return that you choose for the illustration.
- Optionally enter what you have invested today to compare it with the coast amount.
- Read the amount needed today and, if you entered savings, whether you are above or below it.
Formula
Growth factor = (1 + yearly return / 100)^years
Coast amount = target amount / growth factor
Your money if left alone = invested today x growth factor
Gap = coast amount - invested today
The coast amount is the present value of the target at the return you enter. A positive gap is what is still needed today, and a negative gap means you are already past it.
A $1,000,000 target in 30 years
With a $1,000,000 target, 30 years and a 7% yearly return, the growth factor is 7.6123, so the coast amount is $1,000,000 / 7.6123 = $131,367.12. Growth must supply $868,632.88 of the target.
If you already have $100,000 invested, it would grow to $761,225.50 on its own, which is 76.1% of the coast amount. You would still need $31,367.12 today. With $200,000 invested you would be above the coast amount by $68,632.88. The 7% is only an example.
What coasting means
Coast FIRE is the idea that once you have invested enough, you can stop adding to the account and let growth carry it to your target while you cover current expenses with work. The coast amount is simply the lump sum that grows into the target at your chosen return.
Because the result depends on the return, it swings widely. A lower return needs a larger coast amount, and the tool lets you try a few values side by side. A return of 0% means the coast amount equals the target.
Using real or nominal returns
If you set the target in today's dollars, enter a return after inflation. If you set it in future dollars, enter a nominal return. Mixing the two overstates or understates how much you need.
This is an illustration of compound growth, not a forecast. Markets rise and fall, and taxes, fees and spending needs are not modeled. To size the target itself, use the FIRE calculator, and for a plan with continuing contributions use the retirement calculator or the present value calculator.
Assumptions and limits
- The return is the same every year and compounds once a year.
- The target and the return use the same dollars, either both inflation adjusted or both nominal.
- No further contributions, taxes, fees or withdrawals are modeled.
- The return is an example you choose, and this page does not claim any rate is likely.
Frequently asked questions
How do I calculate my Coast FIRE number?
Divide your target by (1 + return) raised to the number of years. With a $1,000,000 target, 30 years and 7%, that is about $131,367 today.
Is the return in this calculator a prediction?
No. It is a number you choose to illustrate compound growth. Real returns vary from year to year and can be negative, so treat the result as a scenario.
What if I already have more than the coast amount?
The tool shows by how much you are above it and what your money would grow to if you left it alone, so you can see how far past the target it could reach.
Should the target be in future or today's dollars?
Either works if you stay consistent. Use a return after inflation with a target in today's dollars, or a nominal return with a target in future dollars.