Coast FIRE Calculator

How much would you need invested today so that compounding alone — no more contributions — grows it into enough to retire on at your target age? That is your Coast FIRE number. Estimate only — not financial advice.

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How sensitive is that number?

The Coast FIRE number depends entirely on the real return you assume — and nobody knows future returns. The band below recomputes everything at two percentage points below and above your assumed real return, so you can see how much the answer moves when the assumption is wrong. A plan that only works at the optimistic end is a fragile plan.

A horizon of more than 60 years is unusually long; the result is highly sensitive to the real-return assumption.

Worked example

Worked examples, not your result — the figures below use the numbers stated in the example. Enter your own numbers in the calculator above for your figure.

Example — the calculator's defaults. Age 35, retiring at 65, $50,000 a year of spending in retirement, $0 saved so far, $1,000 a month in contributions, 10% investment return, 3% inflation, no fees, 4% withdrawal rate. The real return is 7%. The full FIRE number is $1,250,000, and the Coast FIRE number — what you need today — is $164,209. Keep contributing $1,000 a month and the portfolio is projected at $1,133,529 at 65, and you reach Coast FIRE in 10 years, at age 45. At a $30 hourly wage, the Coast number is 5,474 hours of work. If the real return were only 5%, the Coast number would be $289,222 and coasting would take 17 years; at 9% real it would be $94,214 and take 7 years.

What this assumes

• The real return (investment return minus inflation minus fees) stays constant over the whole horizon — no sequence-of-returns risk, no market crashes beyond what your inputs say.
• Contributions happen at the end of each year; your monthly contribution is annualised (× 12).
• No taxes of any kind are applied — no tax on gains, no tax on withdrawals, no tax-advantaged accounts. All figures are in today's dollars.
• Investment fees are limited to the fee percentage you enter, deducted from the annual return.
• The safe withdrawal rate is a fixed percentage of the retirement portfolio (the 4% rule from the Trinity Study, 1998) — adjustable above.

How this calculator works

Your full FIRE number is your annual retirement spending divided by your safe withdrawal rate. Your Coast FIRE number discounts that target back to today at the real return over the years until retirement: FIRE number ÷ (1 + real return)^years. The projected portfolio compounds your current savings and your monthly contributions at the same real return. Years-to-coast is the first year your projected portfolio reaches the Coast number. The sensitivity band repeats the same calculation at two percentage points below and above your real return. The math follows the open-source Coast FIRE calculator by CoastFIRE Hub (MIT licensed); FigWage's page, copy and layout are original.

Common questions

What is Coast FIRE?
Coast FIRE is the amount you need invested today so that investment growth alone — with no further contributions — grows it into your full retirement target by the age you plan to retire. Once you have reached your Coast FIRE number, you can stop adding to retirement savings and still expect to retire on schedule, as long as the assumed returns hold.

Why use a 4% safe withdrawal rate?
The 4% rule comes from the Trinity Study (Cooley, Hubbard & Walz, 1998), which tested how much a retiree could withdraw each year from a stock-and-bond portfolio without running out of money over 30 years. It is a widely cited rule of thumb, not a guarantee — you can change the withdrawal rate in this calculator to see how the answer moves.

What if my investment return is below inflation?
Then your money does not grow in real terms, and compounding cannot do any of the work for you. The calculator says so plainly and sets your Coast FIRE number equal to your full FIRE number — you would need the entire retirement target saved today.

Does this calculator include taxes?
No. It models no taxes of any kind — no tax on gains, no tax on withdrawals, no tax-advantaged accounts. Treat the figures as pre-tax planning estimates in today's dollars, and talk to a tax professional before making decisions that depend on the tax treatment.

Why does the answer show a range instead of one number?
Because the answer depends entirely on the real return you assume, and nobody knows future returns. The sensitivity band recomputes your Coast FIRE number at two percentage points below and above your assumed real return, so you can see how much the answer moves when the assumption is wrong. A plan that only works at the optimistic end is a fragile plan.

Sources

Math: Coast FIRE formulas as published in the open-source FIRE calculator by CoastFIRE Hub (coastfirehub/fire-calculator, MIT License). Default assumptions follow that calculator's stated sources: 10% investment return (S&P 500 historical nominal average since 1926), 3% inflation (US CPI historical average), 4% safe withdrawal rate (Trinity Study, Cooley, Hubbard & Walz, 1998). All three are adjustable on this page — they are starting points, not forecasts. FigWage calculations and assumptions are documented on our methodology & sources page. Page checked November 2026.

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Estimate for general information only — not tax, legal, or financial advice. No taxes are modelled on this page. Coast FIRE math adapted from the open-source FIRE calculator by CoastFIRE Hub (MIT License — see LICENSE.md in this tool's directory); FigWage code, copy and layout are original. See our methodology & sources.