Coast FIRE Calculator
Coast FIRE is the balance at which you could stop contributing today and still reach your full FIRE number by retirement through growth alone. Enter your current balance, age, and target retirement to see whether you've hit it — and if not, what closes the gap.
After inflation. This growth has to do all the work once you stop contributing.
4% is the classic "4% rule" used to size your FIRE number.
Not coasting yet
Your Coast FIRE number is $93,663 — the balance that, left alone at a 7.0% real return for 35 years, grows into your $1,000,000 FIRE number by age 65. You're $43,663 short of that today.
COAST FIRE NUMBER
$93,663Needed today to coast to age 65
YOUR BALANCE
$50,000GAP TO COAST
$43,663One-time lump sum, today
$43,663
Add this once and you could stop contributing immediately.
Or, keep contributing monthly to age 65
$263/mo
Reaches your $1,000,000 FIRE number by age 65 without ever coasting.
Growth-only projection from your current balance — assumes zero further contributions, in today's (real) dollars.
Why the Coast FIRE number shrinks the more time you have
Coast FIRE takes the same FIRE number used everywhere else on this site — annual expenses divided by a withdrawal rate, most famously 4% (25x expenses), from William Bengen's 1994 research and the 1998 Trinity Study — and asks a present-value question instead of a future-value one. Instead of "how much do I need to contribute to reach this by retirement," it asks "how much would I need today, contributing nothing more, to grow into that number by retirement." The further away retirement is, the more years compounding has to work, so the same destination requires a smaller balance today.
That's why Coast FIRE resonates most with people early in their working years: someone at 28 targeting retirement at 65 has 37 years of growth doing the heavy lifting, while someone at 55 targeting the same retirement age has only 10. The math is identical — it's the exponent that changes.
The same honesty check applies here as with any FIRE number: this is a backtest-derived planning heuristic, not a guarantee. A real (inflation-adjusted) return assumption that turns out to be too optimistic, a change in target spending, or moving up your retirement date all shift the Coast FIRE number — recalculate periodically rather than treating a single run as final.
Frequently asked questions
What is Coast FIRE?
Coast FIRE is the point at which your current investments are large enough that, left to grow untouched, they'll reach your full FIRE number by your target retirement age through investment returns alone — no more contributions required. You could stop saving for retirement entirely (while still covering current living costs from income) and still get there.
How is the Coast FIRE number calculated?
First, your FIRE number is your target annual retirement spending divided by your withdrawal rate (25x at the classic 4% rate). The Coast FIRE number is that figure discounted backward to today at your expected real return, over however many years remain until your target retirement age — the balance that compounds, on its own, into the FIRE number by then.
If I've hit Coast FIRE, does that mean I should stop contributing?
Not necessarily — it's descriptive, not prescriptive. Hitting Coast FIRE means the retirement math no longer requires more contributions; it doesn't mean continuing to contribute is wrong. Many people who reach Coast FIRE choose to keep saving to retire earlier than their target age, build a larger buffer, or downshift to lower-paying, more flexible work instead of stopping outright — that flexibility is usually the actual point.
What if I haven't hit Coast FIRE yet?
The calculator shows two ways to close the gap: a one-time lump sum today that gets your balance to the Coast FIRE number immediately, or a level monthly contribution kept up all the way to your target retirement age that reaches the full FIRE number without ever technically coasting. Most people land somewhere in between — reduce contributions as the gap closes rather than picking one extreme.
Does a longer time horizon make Coast FIRE easier or harder to reach?
Easier, all else equal — more years until retirement means more time for compounding to do the work, so the Coast FIRE number (discounted back from the same FIRE number) is smaller. That's also why Coast FIRE is most often discussed by people in their 20s and 30s: the same balance simply has more runway to grow.
Should I use a different withdrawal rate for Coast FIRE than for a standard FIRE calculation?
The withdrawal rate assumption feeds the same FIRE-number math either way (see the /fire-calculator/ FAQ for the Trinity Study and Bengen research behind it, and its caveats over a long retirement). If your Coast FIRE plan implies retiring later at a traditional age, a rate near 4% is more defensible than for someone planning a 50-year retirement starting at 35, where a lower rate (3-3.5%) is more commonly used.
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