Let it grow

Coast FIRE calculator

Coast FIRE is the point where what you have already invested could grow to your FIRE number by retirement on its own, so you only need to earn enough to cover today's costs.

The outlook

To coast from today you would need $274,094 invested; you have $90,000, so $184,094 short. Left alone, your savings would reach the FIRE number at about age 93.

FIRE number: $1,000,000
Coast number today: $274,094
Years until 65: 33
Your savings alone reach it at: age 93

Needed to coast, and your savings, by age

Needed at each age to coast
Your savings, left to grow

Point at the chart, or focus it and use the arrow keys, to read any age.

The coast number

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

The FIRE number is your yearly retirement spending divided by the withdrawal rate you choose. The coast number is what that target is worth today: the sum that, with no further deposits, would grow to it by your retirement age at the real (after-inflation) return you enter.

The chart draws both sides. The rising line is the amount you would need at each age to coast from then on; it climbs because the time left to grow shrinks. The shaded line is your current savings left to grow. Where your savings sit above the rising line, they could reach the target on their own, on these assumptions.

Example: spending $40,000 a year at a 4% rate gives a $1,000,000 target. At 32, retiring at 65 with a 4% real return, the coast number is about $274,094. With $90,000 invested you are about $184,094 short; left alone, those savings would reach the target only around age 93.

Coasting is a planning idea, not a guarantee: a lower return than you assumed, a longer retirement or higher spending all raise the number. Recheck it as years pass.

Sources

U.S. Securities and Exchange Commission, Investor.gov Compound Interest Calculator.
William P. Bengen, “Determining Withdrawal Rates Using Historical Data”, Journal of Financial Planning, October 1994 (reprinted by the Financial Planning Association, 2004).
Philip L. Cooley, Carl M. Hubbard and Daniel T. Walz, “Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable”, AAII Journal, February 1998 (the “Trinity study”).

Questions

Do I stop saving when I reach coast?

That is the idea behind the name: you would still need to cover your current living costs, but not add to retirement savings. Whether that suits you depends on how sure you are of the assumptions; this page only does the arithmetic.

Why a real return?

The target is in today's money, so the growth has to be after inflation too. Subtract your inflation assumption from your expected return before entering it.

What if I retire earlier?

Fewer years to grow means a bigger coast number. Move the retirement age and watch the rising line shift; the FIRE number itself stays the same unless your spending or rate changes.