Coast FIRE: how much you need by age

What coast FIRE means

Coast FIRE is the point where your investments, left alone, will grow to your FIRE number by a normal retirement age. From then on you can stop adding to the portfolio. You still need to earn enough to pay your living costs until you retire, but you no longer need to save for retirement, which is why some people use it to work fewer hours or switch to a job they prefer.

The formula

Coast FIRE number = FIRE number ÷ (1 + r)^{years to retirement}

r is the return after inflation. For a $1,000,000 goal at 65, starting at 35 with 5%: $1,000,000 ÷ 1.05³⁰ = $1,000,000 ÷ 4.3219 = $231,377.

How much you need by age

Coast FIRE number for a $1,000,000 goal at 65, at three returns after inflation:

At 5%, you need $142,046 at 25 and $376,889 at 45, so each year you wait raises the amount by about 5%. For a $1,500,000 goal multiply by 1.5: at 35 and 5%, $347,066.

How long it takes to get there from zero

Starting with nothing invested, the age you reach coast FIRE for a $1,000,000 goal at 65, at 5% after inflation:

Starting at 25 with $15,000 a year, saving can stop at 38.1. Starting at 35, $15,000 a year does not get there before 65; with $20,000 a year, saving can stop at 52.7.

Retiring before or after 65

The coast number depends on the age you plan to stop working. For someone who is 35 today with a $1,000,000 goal and 5% after inflation:

Retiring earlier also means the money has to last longer, which usually calls for a lower withdrawal rate and a bigger FIRE number. The 4% rule explained shows how the rate changes with the length of retirement.

Real vs nominal returns

The coast number is very sensitive to the return. If you enter 10% without saying whether it is before or after inflation, the number at 35 looks like $57,309. The goal is in today's dollars, so the return has to be after inflation as well: 10% with 3% inflation is 6.8% real, and you need $139,103. The coast FIRE calculator does that conversion when you choose "Before inflation".

Coast FIRE vs barista FIRE

Coast FIRE stops the saving and keeps the work: earnings pay all your spending until retirement. Barista FIRE stops full-time work: part-time income pays part of your spending and the portfolio pays the rest, from the start. Both are compared with the same household in lean vs fat vs coast vs barista FIRE.

Questions people ask

How much money do I need for coast FIRE?

Your FIRE number divided by the growth you expect until retirement. For $40,000 a year at 4% (a $1,000,000 FIRE number) and 5% a year after inflation, that is $181,290 at 30 and $295,303 at 40.

What is my coast FIRE age?

The age at which your portfolio reaches the coast number for that age. Worked example: at 30, with $50,000 invested and $15,000 saved a year at 5% after inflation, coast FIRE for a $1,000,000 goal at 65 arrives at 41.8. The $322,371 invested at that point grows to $1,000,000 by 65 with no more saving.

What is the difference between coast FIRE and traditional FIRE?

With traditional FIRE the portfolio already pays your spending. With coast FIRE it will by retirement age, so you keep working until then. For the household in the FIRE calculator, coast FIRE comes at 41.2 and full FIRE at 53.8, 12.5 years apart.

Calculate your coast number

Enter your age, retirement age, spending and savings in the coast FIRE calculator to see your coast number and the age you reach it.

Sources

• William P. Bengen, "Determining Withdrawal Rates Using Historical Data", Journal of Financial Planning, October 1994.
• U.S. Bureau of Labor Statistics, Consumer Price Index.