Coast FIRE Calculator
Find out if your current savings will coast to a full retirement with no further contributions — and your exact Coast FIRE number.
A Coast FIRE calculator tells you the amount you need invested today so that compound growth alone — with no further contributions — reaches your full retirement target by your retirement age. Coast FIRE is the point where the saving is done even though the working is not: you still need to earn enough to cover current living expenses, but every dollar of future retirement funding is already in the market compounding. People use it as a milestone that unlocks downshifting — part-time work, a lower-paying but preferred career, a sabbatical — without giving up the retirement date.
Enter your age, retirement age, current invested savings, expected spending, and return assumptions above. The tool computes your Coast FIRE number, projects what your current savings grow to by retirement, and gives a clear verdict: reached, or short by a stated amount.
How it's calculated
The calculation is the compound-interest formula run in reverse. First the full retirement target from the safe-withdrawal-rate framing:
FIRE target = annual spending ÷ withdrawal rate (4% ⇒ 25× spending)
Then that target is discounted back to today at your expected real return:
Coast FIRE number = FIRE target ÷ (1 + r)n
where r is the real (inflation-adjusted) annual return and
n the years until retirement. The projection of your current
savings is the same formula run forward: FV = savings × (1 +
r)n. Because n sits in an exponent, time
is the dominant variable — every extra year of compounding lowers the
number today meaningfully. Full formulas, including the
Bengen and Trinity-study origins of the 4% rule, are on our
methodology page.
Worked example: $50,000 spending, retiring at 65
Take the calculator's default scenario: retirement spending of $50,000 a year at a 4% withdrawal rate — a $1,250,000 target — with a 5% real return. Here is the Coast FIRE number at different starting ages, computed with the same engine as the tool above:
| Age today (retire at 65) | Years of compounding | Coast FIRE number | Share of $1.25M target |
|---|---|---|---|
| 25 | 40 | $177,557 | 14% |
| 30 | 35 | $226,613 | 18% |
| 35 | 30 | $289,222 | 23% |
| 40 | 25 | $369,128 | 30% |
| 45 | 20 | $471,112 | 38% |
| 50 | 15 | $601,271 | 48% |
The exponent does the work: a 25-year-old needs only 14% of the final target invested to coast, while a 50-year-old needs nearly half. The calculator's default case — a 32-year-old with $120,000 invested — has a Coast FIRE number of $249,841, so they are $129,841 short of coasting: their current savings alone grow to about $600,383 by 65, well under the $1,250,000 target. The verdict flips entirely on continued contributions until the balance crosses $249,841. Note also that the Coast FIRE number rises each year you age (there is less time left to compound), so it is a moving target that should be re-checked as your spending estimate and timeline evolve.
When should you use this calculator?
Use it to locate yourself on the timeline: given what you have invested today, is the retirement problem already solved by compounding, and if not, how far off is it? It is the right tool for testing a downshift before you take it — if you stopped contributing at the end of this year, what would your balance grow to by retirement, and does that clear your target? It also quantifies sensitivity: re-run it at a 4% real return instead of 5%, or with retirement at 60 instead of 65, and watch how much the required amount moves. Because the answer is so assumption-driven, the honest use is a range — optimistic and conservative inputs, bracketing your number — rather than a single figure. For the full target itself and the years-to-FIRE math with ongoing contributions, see the FIRE calculator.
The tool answers the arithmetic question only. Whether coasting is wise — job-market re-entry risk, healthcare coverage before retirement age, the possibility of spending changes — is outside the math.
Assumptions and limitations
- The return is a constant real (inflation-adjusted) rate, compounded annually. Real markets deliver volatile returns; the same average with a bad early sequence produces a different outcome.
- The 4% rule is a historical heuristic from U.S. stock-and-bond data over 30-year retirements, not a guarantee — early retirees with longer horizons often use 3–3.5%, which raises both the target and the Coast number.
- Enter returns net of inflation and fees. Using a nominal return (say 8–10%) silently understates your Coast FIRE number in today's dollars.
- Taxes are not modeled. Withdrawals from pre-tax accounts are taxable, so gross spending needs may exceed the figure you enter.
- No further contributions are assumed after today — that is the definition of coasting. Any continued saving only improves the outcome.
- Outside income in retirement (Social Security, pensions, rentals) is not modeled; it reduces the spending your portfolio must cover and therefore your target.
This page is educational content about the Coast FIRE calculation. It is not financial advice and does not consider your personal circumstances. For decisions that matter, consult a qualified professional.
Last reviewed: 2026-07-09