Coast FIRE is the amount you need invested today so that, with no further contributions, compound growth alone reaches your retirement nest egg by your target age. After hitting it, you only need to cover current expenses.

How is the Coast FIRE number calculated?

Take your retirement nest egg target and discount it back to today using your expected real (inflation-adjusted) return over the years until retirement. The result is what you need invested now.

Does the Coast FIRE number change with age?

Yes, dramatically. The younger you are, the smaller the number, because you have more years of compounding. Waiting even a decade can roughly double what you need invested today.

Retirement · Honest math, no agenda

Coast FIRE: the number that lets you stop saving

There is a number that, once you hit it, means you can stop saving for retirement entirely, keep working and spending your paycheck, but never contribute another dollar, and still end up with a full nest egg. It is called Coast FIRE, and for someone young it can be surprisingly small.

What Coast FIRE actually means

Normal retirement math asks how much you need saved by 65. Coast FIRE flips it: how much do you need invested right now so that, with zero further contributions, compounding alone carries you to your number by retirement? Once you have that amount, your future is on autopilot, you only work to cover today's life.

A worked example

Age 32, retiring at 65, spending $50,000/year in retirement (a $1,250,000 nest egg at a 4% withdrawal rate), assuming 7% returns and 3% inflation:

FI target (nest egg needed): $1,250,000
Coast FIRE number (invested today): $355,528
That amount, untouched, grows to your full nest egg by 65

So $355,528 invested now, with no further contributions, becomes $1.25M by 65, because you have 33 years for it to grow. Time does almost two-thirds of the work.

Find your Coast FIRE number →Free Coast FIRE calculator. No sign-up. Enter your age, spending, and assumptions.

Why age is everything

The Coast FIRE number is brutally sensitive to age, because it is all about how many years of compounding you have left. At 32 you might need about $355k; the same person at 45 needs roughly double, and at 55 nearly the whole target. This is the real reason "start early" is not a cliche, a dollar invested young is worth several times a dollar invested later.

The honest caveat

This assumes your money stays invested and earns something like your expected return, and markets do not move in a straight line. It frees you from saving more, not from working, you still cover today's expenses. Use a lower withdrawal rate for more cushion, and re-check every few years.

Figures from TheSharpDollar's Coast FIRE calculator using the sample scenario. Your result depends on your age, spending, and return assumptions.