Coast FIRE Calculator
Coast FIRE is the point where your existing investments, left completely alone, will grow into your full FIRE number by the time you retire — without adding another dollar. Enter your FIRE target, what you have invested today, your age, your planned retirement age, and an expected real return, and this calculator finds the present value that coasts to your goal, then shows the gap between that number and your current savings. It is a planning estimate, not financial advice.
Your plan
Use a real(inflation-adjusted) return with a target in today's dollars to keep the result in today's purchasing power.
Coast FIRE number
$131,367.12
Invested today, this grows to $1,000,000.00 in 30 yrs at 7.00% real
Still to invest
$51,367.12
Current savings grow to
$608,980.40
Coast FIRE detail
Growth to your FIRE number (no contributions)
Compare scenarios
Run the same calculation with two or three input sets side by side. Differences are highlighted; every number comes from the same tested formula as the calculator above.
| Input | Scenario A | Scenario B |
|---|---|---|
| Target Fire Number | ||
| Current Savings | ||
| Current Age | ||
| Retirement Age | ||
| Real Return Pct |
How it works
The coast number is the present value of your FIRE target discounted back over the years until retirement: coastNumber = targetFireNumber ÷ (1 + r)^years, where r is your expected real annual return and years is retirementAge − currentAge. This is just compound interest run in reverse. Once your invested balance reaches this figure, ordinary market growth alone is mathematically enough to reach your FIRE number by your target age — you no longer need to contribute new money to stay on track.
The gap is simply coastNumber − currentSavings. A positive gap is how much more you need invested today to be coasting; a negative gap means you have already passed the coast point and the calculator flags you as coasting. Reaching Coast FIRE does not mean you can stop working — it means you can stop investing for retirement. You still have to cover your living expenses out of current income until you actually retire and start drawing down the portfolio.
Because the coast number depends heavily on your assumed return and time horizon, small changes move it a lot. A longer runway or a higher return compresses the number sharply (more years of compounding do the heavy lifting), while a shorter runway pushes it toward the full FIRE target. The model assumes a single constant real return every year, which real markets never deliver — so treat the result as a directional target and revisit it as your assumptions and balances change.
Frequently asked questions
Does hitting Coast FIRE mean I can retire now?+
No. Coast FIRE only means your retirement investing is done — the balance you already have should grow into your FIRE number by your target age on its own. Until you actually retire, you still need income to cover your day-to-day living expenses, because you are not yet drawing from the portfolio. Many people at Coast FIRE keep working but redirect what they used to invest toward spending, part-time work, or a career change. Full FIRE, where work becomes optional, comes later when the portfolio itself can fund your lifestyle.
Why does the assumed return matter so much?+
The coast number is the FIRE target divided by (1 + return)^years, so the return compounds over your entire runway and the result is extremely sensitive to it. Assuming 9% instead of 5% real can cut the coast number substantially over 30 years. This calculator uses a single constant real return, but actual markets are volatile and average returns are uncertain, so a modest, conservative assumption (many planners use 4–7% real) gives you a margin of safety. If your real return comes in lower than assumed, you will reach your FIRE number later than the model suggests.
What about sequence-of-returns risk and inflation?+
This model uses a smooth constant return and cannot capture sequence risk — the danger that a poor run of returns early on, especially near retirement, leaves you short even if the long-run average is fine. Using a real (inflation-adjusted) return with a target expressed in today's dollars keeps the whole calculation in today's purchasing power, but it still ignores taxes, fees, and the real-world lumpiness of markets. Treat the coast number as a checkpoint to revisit regularly, not a guarantee, and build in a buffer rather than assuming the best case.