Coast FIRE Calculator
Enter your age, portfolio and retirement target to find your Coast FIRE number — the amount that, left to grow with no further contributions, reaches your FIRE number by your target retirement age.
Use a return already net of expected inflation if your spending figure is in today's money.
Coast number if you start coasting...
How this is calculated
Your FIRE number is your target annual retirement spending divided by your withdrawal rate (spending ÷ withdrawal rate, e.g. $40,000 ÷ 4% = $1,000,000) — the portfolio size that supports that spending indefinitely at that withdrawal rate.
Your Coast FIRE number today is the amount that, growing at your assumed return with zero further contributions, reaches that FIRE number by your target retirement age. It's calculated by discounting the FIRE number backward at your expected return over the years remaining — more years remaining means a smaller number is needed today, since compounding has longer to work.
This runs a real month-by-month simulation rather than a single formula: it tracks your portfolio growing with your actual monthly contribution, and at every month it recalculates the required coast target against the years remaining at that point (which keeps shrinking as time passes). The month your simulated portfolio first meets or exceeds that moving target is the month contributions could stop and compounding alone would still get you there on schedule.
The 'coast number if you start coasting in 5 or 10 years' reference figures show the actual cost of waiting: because there's less time left for growth to do the work, the number needed to coast rises the longer you keep contributing before stopping — all else equal.
Frequently asked questions
What is Coast FIRE?
Coast FIRE is the point where your existing investments, left alone with no further contributions, are projected to grow (through compounding alone) into a full FIRE number by your target retirement age. Reaching it doesn't mean you stop working — most people keep working, just without the pressure to keep saving aggressively, since growth is already on track to finish the job.
What return rate should I use?
A commonly used starting point is a long-run diversified-portfolio average, adjusted down for inflation if your spending figure is already in today's money (a 'real' return). This calculator doesn't apply a separate inflation adjustment — whatever return you enter is applied directly, so make sure it matches how you entered your spending figure.
What if I've already passed my Coast FIRE number?
The calculator shows your surplus instead of a gap, and 'time to reach Coast FIRE' shows as already there. A surplus means compounding alone is on pace to exceed your FIRE number by retirement even without any further contributions — contributing anyway would get you there earlier, or support a higher retirement spending target.
Does this account for inflation?
Not separately — it applies your entered return rate directly to your entered spending figure. If your retirement spending figure is in today's purchasing power, enter a return rate that's already adjusted for expected inflation (a 'real' return) rather than a raw nominal market average.
Sources
- Trinity Study (1998) and related safe-withdrawal-rate research — basis for the common 4% withdrawal-rate convention
- Coast FIRE / Barista FIRE terminology as used across the FIRE (Financial Independence, Retire Early) community
Disclaimer
This tool provides an estimate for informational purposes based on the figures and return assumption you enter and isn't financial advice. Actual investment returns vary year to year and aren't guaranteed; a sustained downturn early in retirement can affect a fixed withdrawal-rate plan more than the average return alone suggests.
Last updated 2026-11-02.