What is Coast FIRE?
Coast FIRE is the moment you've saved enough that your investments — left completely alone — will grow into a full retirement nest egg by the age you want to stop working. You keep earning a living, but you never need to save another dollar. The pressure lifts: you can downshift to a lower-stress job, take a sabbatical, start a business, or simply breathe, because compounding has taken over the heavy lifting.
The number that defines this moment is your coast number: the portfolio size at your current age that guarantees your target retirement fund, assuming a realistic market return and nothing but time. This calculator finds yours, tells you how far along you are, and gives you a verdict you can act on — coasting, on track, or behind with a concrete fix.
The Coast FIRE formula, explained honestly
The math has three steps.
- FIRE number = gross annual spending ÷ safe withdrawal rate. Spend $36,000 a year and withdraw 4%? You need $900,000 at retirement. If you set a retirement tax rate, we gross your spending up so the target covers pre-tax income. Add a pension or Social Security and we split the problem into a bridge phase and a post-pension phase, discounting each properly.
- Coast number = FIRE number ÷ (1 + r)years to retirement, where r is your real return. This is just the compound-growth formula run backwards: how much money today grows into the FIRE number by itself.
- Your progress = current investments ÷ coast number. Cross 100% and you're coasting. Below it, the solver finds the exact age at which your contributions and growth catch up — your coast age.
One detail most calculators get wrong: the real return. The correct conversion is r = (1 + nominal) ÷ (1 + inflation) − 1, not nominal minus inflation. With the classic 7% return and 3% inflation, the difference looks tiny (3.88% vs 4%) but compounds to roughly a 3–4% overstatement of your portfolio over 30 years — enough to make you think you've hit your coast number years early. Every projection on this page is computed in real terms, so all numbers are in today's dollars, and monthly contributions compound monthly at the equivalent real monthly rate.
A worked example
Maya is 32 with $150,000 invested. She spends $3,000 a month and plans to retire at 65. She assumes a 7% nominal return and 3% inflation, so her real return is about 3.88%.
- FIRE number: $36,000 ÷ 4% = $900,000 at age 65.
- Coast number at 32: $900,000 ÷ 1.038833 ≈ $256,000. Maya is about 59% of the way there.
- Contributing $700 a month, her portfolio crosses the moving coast number around age 50 — after that, every dollar she saves is optional.
Notice what the verdict does not say: it doesn't claim Maya can retire at 50. Coast FIRE means her retirement fund is locked in, not that she can stop covering her monthly bills. That distinction is the whole point.
Reading your verdict
✓ Coasting (coral): your investments already exceed your coast number. Compounding finishes the job on schedule; keep saving only if you want a buffer.
On track (emerald): you're not coasting yet, but at your current contribution rate you will be — the subline names the exact age. The chart shows both futures: the solid line if you keep contributing, the dashed line if you stop today, with your coast point marked where the dashed future stops being enough.
Behind (amber, never red): at this pace you'd fall short, so the panel shows what it takes — either an extra monthly contribution that lands you on time, or the later retirement age your current pace supports. We show whichever change feels cheaper. And because markets don't move in straight lines, flip the crash test to replay your verdict with your portfolio cut 30%: “if markets dropped tomorrow,” would the plan still hold?
When Coast FIRE doesn't work
Coast math assumes steady average returns over decades — it is weakest when your horizon is short (under about 10 years, a bad decade can dominate) or when your spending is high relative to what you can save. It also assumes you can actually stop saving; if your career income is volatile, treating your coast number as a floor rather than a finish line is the prudent move. Past returns don't guarantee future ones, and this page is education, not personalized investment advice — but the arithmetic of compounding is a reasonable place to start planning.
Frequently asked questions
What is the difference between Coast FIRE and regular FIRE?
Regular FIRE means your portfolio already covers your full spending today — you can stop working for good. Coast FIRE is the earlier checkpoint where you have just enough invested that compounding alone will grow it into your full FIRE number by your planned retirement age. You still work to pay your bills, but you no longer need to save.
How is the coast FIRE number calculated?
Your FIRE number is your gross annual spending divided by your safe withdrawal rate (spending $36,000 a year at a 4% SWR gives $900,000). Your coast number today is that FIRE number discounted back to the present: FIRE number ÷ (1 + real return)^years until retirement. With roughly 39 years of compounding ahead, $900,000 becomes about $190,000–$260,000 depending on the return you assume.
What return rate should I assume?
The calculator defaults to a 7% nominal return with 3% inflation — close to long-run global equities — but everything is adjustable in Advanced settings. The key detail: we convert nominal to real using (1 + nominal) ÷ (1 + inflation) − 1, not simple subtraction, so every number you see is in today's dollars.
Does the coast FIRE number include taxes and Social Security?
It can. Set a retirement tax rate and we gross up your spending so your portfolio targets the pre-tax income you actually need. Add an expected pension or Social Security amount and its start age, and the engine computes a two-phase FIRE number: a bridge fund that covers you until the pension starts, plus a smaller nest egg for the years after.
What if the market crashes right after I hit my coast number?
Flip the crash-test toggle to replay your verdict with your investments cut 30%. A crash delays compounding but contributions and time usually recover it — the toggle shows honestly whether your plan survives. If the amber verdict worries you, a lower assumed return or a later retirement age is the conservative fix.
More FireVerdict calculators
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