Coast FIRE Calculator
Find your Coast FI number, the savings you need today so compound growth alone takes you to retirement, even if you stop investing now.
Coast FIRE number by age
Your Coast FIRE number is the amount that, left invested with no further contributions, grows to your retirement target on its own. Example: to spend $40,000/year from age 65 (a $1,000,000 portfolio at a 4% withdrawal rate), assuming 5% real (after-inflation) growth, you’d need this much already invested at each age:
| Current age | Years of growth left | Coast FIRE number today |
|---|---|---|
| 25 | 40 | $142,046 |
| 30 | 35 | $181,290 |
| 35 | 30 | $231,377 |
| 40 | 25 | $295,303 |
| 45 | 20 | $376,889 |
| 50 | 15 | $481,017 |
| 55 | 10 | $613,913 |
Coast number = target ÷ (1 + real return)^(years to 65). Real return means after inflation, so figures are in today’s money. Set your own spending, ages, and rates in the calculator above, or work out the full target with the FIRE calculator.
Default inflation rate: 3.0% per year, based on long-run global CPI averages data (2026). You can override it in each calculator’s advanced options. See data sources for full citations.
How We Work It Out
The Coast FI Number is derived by discounting your full FIRE target back to today:
Where: SWR = safe withdrawal rate (e.g. 0.04 for 4%), i = annual inflation rate, r = annual investment return, n = years to retirement.
Real-World Examples
A 30-year-old targeting retirement at 55
With $50,000 in annual expenses, their FIRE number today is $1,250,000 (at 4% SWR). Inflated at 2.5% over 25 years, the target at retirement is about $2,316,000. Discounted back at 8% return, their Coast FI number today is around $339,000. If they have $339,000 saved at 30, they can stop contributing and just let it compound.
Frequently Asked Questions (FAQ)
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