Coast FIRE: when you can stop saving for retirement

What is Coast FIRE?

Coast FIRE is the moment your invested savings are large enough that, with no further contributions, they will grow to your full retirement target by the time you plan to stop working. FIRE stands for Financial Independence, Retire Early; "coasting" is the stretch after you've done the heavy saving, when compounding carries the load and you just leave the money alone.

The number that matters is your Coast FIRE number: the amount you need invested today to reach that target on autopilot. Hit it, and every dollar you would have saved for retirement is suddenly yours to spend, or to work less for. You haven't retired — you've just crossed the finish line on the saving part, decades before the money is due.

How is Coast FIRE different from retiring early?

This is where most people trip. Reaching Coast FIRE does not mean you can stop working. It means you can stop saving for retirement. You still need an income to cover this month's rent, groceries, and bills — you've just pre-funded your seventies, so none of today's paycheck has to go toward them.

Regular FIRE is the later milestone: your portfolio is big enough to pay your living costs outright, and you can walk away from work entirely. Coast FIRE usually arrives many years — sometimes decades — earlier, because the target it aims at is a future amount that compounding still has time to build. One frees your paycheck; the other frees your time.

How do you calculate your Coast FIRE number?

It takes two steps. First, find your FIRE number — the full amount you eventually need. The common rule is to divide your yearly retirement spending by a safe withdrawal rate, the slice of a portfolio you can pull each year without draining it. At the widely used 4% rate, $40,000 of annual spending needs $40,000 ÷ 0.04 = $1,000,000.

Second, work backward. Your money has years to grow before retirement, so you don't need the whole million today — you need however much will become a million by then. Divide the FIRE number by your expected growth over those years:

Coast number = FIRE number ÷ (1 + real return)^years

"Real return" means the growth rate after inflation is stripped out, which keeps every figure in today's dollars. Say you're 30, retiring at 65 — that's 35 years — and you expect a 5% real return. The math is $1,000,000 ÷ 1.05³⁵ = $1,000,000 ÷ 5.52, or about $181,290. Put that much in today, add nothing more, and it grows to the full million. Compounding supplies the remaining $818,710 — roughly 82% of your entire retirement — for free.

Why does starting younger matter so much?

Because the coast number depends largely on how many years of growth you have left, and those years are worth more than most people guess. Every year you wait is a year of compounding you can't get back, so the amount you need today climbs fast — not in a straight line, but a steepening curve.

Here's the same $1,000,000 target at a 5% real return, from different starting ages:

Look at the jump from 30 to 45. Waiting those 15 years more than doubles what you need today, from $181,290 to $376,889 — for the exact same finish line. The early saver isn't just ahead; the years themselves are doing most of the work, and there's no way to buy them back later.

Why does the number swing so wildly?

The single input that moves the coast number most is the return you assume — and it's where an honest estimate and a rosy one split apart. The rate has to be a real return, already adjusted for inflation, so it matches a target measured in today's dollars. A calculator quietly using a nominal figure like 10% against that same target would tell you you need far less than you really do.

Even the right kind of number can be set too high. A 100% stock portfolio has returned roughly 6–7% a year after inflation over the very long run, but that's a historical ceiling, not a promise — banking decades on it assumes the best average repeats with no rough patch, on a portfolio that's all stocks. Most planners coast on about 5% real instead, and anything less stock-heavy lands lower.

The gap isn't small. At 30, assuming 7% instead of 5% cuts the coast number from $181,290 to about $93,663 — nearly cutting it in half. So a rosier rate can tell you you're already coasting when a cautious one says you're only halfway there. When in doubt, use a lower, inflation-adjusted rate: the cost of being too cautious is saving a bit more than you had to; the cost of being too optimistic is finding out at 60.

What Coast FIRE quietly assumes

Coasting is a genuinely useful milestone, but it rests on a few assumptions worth saying out loud. It assumes you keep earning enough to cover today's expenses without touching the portfolio — the whole plan breaks the moment you dip into it, because you'd be spending the growth it needs. It also assumes your money actually earns the average return you planned on, in an order that cooperates; a rough first decade can leave you behind even if the long-run average holds.

And it assumes the target itself stays put. If your future spending rises, or inflation runs hot, or you retire earlier than 65, the million you're aiming at grows and your coast number grows with it. Treat the figure as a checkpoint to revisit every few years, not a switch you flip once and forget.

The engine under all of this is compounding — money earning returns on its own past returns. If that still feels abstract, spend two minutes with The Rule of 72, learned by doing to feel how a growth rate sets how fast money doubles.

Frequently asked questions

Last reviewed July 2026. Figures use a 4% withdrawal rate and a 5% real (after-inflation) return unless noted, compounded yearly, and are rounded to the nearest dollar. This guide is for education, not financial advice.