Coast FIRE calculator

What your coast FIRE number is

Coast FIRE is the point where the money you have invested, left alone, grows to your full FIRE number by the age you want to retire. This Coast FIRE calculator finds your coast number: the balance that does that with no more contributions. If you have more than that, you have reached coast FI. If you have less, the gap shows how much work your future contributions still have to do.

How to calculate coast FI

There are two steps. First, find your FIRE number for the age you want to retire: a year of spending times a multiple of 25 to 31, depending on that age. Second, divide it by what your money will grow by in the years between. In short: coast number = FIRE number at your target age ÷ growth between now and then. The calculator does both and also shows the age your current balance reaches FI if you add nothing.

How to use this calculator

Enter your age, the age you want to retire, what you have invested today, and the monthly spending you expect in retirement. Spending sets the FIRE number that your balance is compared against. The calculator assumes a 6% annual return compounded monthly, runs in your browser and saves nothing.

A worked example

Say you are 34, want to retire at 60, have $120,000 invested and expect to spend $4,000 a month. The FIRE number for age 60 is $1,296,000. Over 312 months, money grows about 4.74 times, so your coast number is $273,397. You have $120,000, which is $153,397 short. Left alone, your balance reaches FI at age 72, 6 mo, later than 60, so contributions still have work to do.

How to read the result

Compare your invested balance with the coast number. Above it, you are past coast FI for that age. Below it, the difference is the size of the gap. The coast number moves a lot with the retirement age you pick: at $4,000 a month it is $273,397 for 60 and $187,675 for 65. Try a few ages before settling on one.

Common mistakes

• Using your current age instead of your target age for the FIRE number. The multiple depends on the age you retire.
• Comparing the coast number with net worth. Only invested money counts, not a home you live in.
• Entering today's spending when retirement will cost something different.
• Expecting a steady return. The calculator uses one average rate; real years differ.
• Forgetting that coasting only covers the retirement target. Spending before then still needs income.

Frequently asked questions

What is a good coast FIRE number?

There is no single good number, because it depends on your spending and on the age you plan to retire. At $4,000 a month, the coast number for retiring at 60 from age 34 is $273,397. Retiring at 65 instead lowers it to $187,675, because the money has 5 more years to grow, and a retirement from 65 uses 25× a year of spending instead of 27×.

How do you calculate coast FI?

Work out your FIRE number for the age you want to retire, then divide it by how much your money grows between now and then. With a 6% annual return compounded monthly, 312 months of growth multiplies a balance by about 4.74, so $1,296,000 needs $273,397 today.

Is coast FIRE the same as FIRE?

No. FIRE means your investments can cover your spending. Coast FIRE means your investments are on track to get there by themselves, so you can stop adding to them. You still need income to pay for life until then.

Does coast FIRE mean I can stop working?

Not by itself. It means the savings you already have are enough to reach your FIRE number by your target age without new contributions. Whatever you spend until then still has to come from somewhere.

What return does the calculator assume?

6% a year, compounded monthly, with no further contributions and no Social Security. Real returns vary from year to year, so treat the result as a projection, not a forecast.