What Is Coast FIRE?
Coast FIRE is the point at which your current retirement savings, left alone with no further contributions, will grow through compound investment returns into a full retirement nest egg by your target retirement age. Once you hit your coast FIRE number, you're technically done saving for retirement — you can "coast" the rest of the way on investment growth alone, and shift your income toward living expenses, a lower-stress job, or other goals, while your retirement accounts keep compounding in the background.
How the Calculator Works
Your FIRE number is the total nest egg needed to sustain your desired annual spending using the safe withdrawal rate (commonly 4%, based on the "Trinity Study" research on sustainable withdrawal rates — some planners now use 3.5% for extra safety on long retirements). Your coast FIRE number works backward from that target: it's the amount you'd need to have saved right now so that, growing at your expected real (inflation-adjusted) rate of return with zero further contributions, it reaches your FIRE number exactly when you plan to retire.
Worked Example
FIRE number: $50,000 ÷ 4% = $1,250,000
Years to retirement: 30
Real return (7% nominal − 3% inflation): ~3.88%
Coast FIRE number: $1,250,000 ÷ (1.0388)^30 ≈ $393,000
With $150,000 already saved, this person still has a gap to close before they can stop contributing — the calculator above shows exactly how large that gap is and, given a monthly contribution amount, roughly how long it would take to close it.
Why Use Real (Inflation-Adjusted) Returns?
This calculator works in today's dollars throughout — your desired spending is entered in today's purchasing power, and growth is calculated using the real rate of return (your expected nominal investment return minus expected inflation). This avoids the common mistake of comparing a future dollar figure grown at a nominal rate against a spending target that was never adjusted for inflation, which would understate how much you actually need.
Reaching Coast FIRE doesn't mean retiring immediately — it means you no longer need to add to retirement accounts to hit your number by your target age. Many people who reach Coast FIRE keep working, but shift toward lower-paying, more flexible, or more fulfilling work since the retirement-saving pressure is off.
Frequently Asked Questions
Regular FIRE means you've already saved your entire FIRE number and can stop working now. Coast FIRE means you've saved enough that it will grow into your FIRE number by a future retirement age on its own — you still need income to cover current living expenses until then, but you no longer need to add to retirement savings.
7% nominal is a commonly used long-term average for a diversified stock-heavy portfolio after accounting for typical fees, though actual returns vary significantly year to year and aren't guaranteed. More conservative planners use 5-6%. Try a range of assumptions rather than relying on a single number.
No — this calculator assumes your desired annual spending is funded entirely from your own retirement savings. If you expect Social Security or a pension to cover part of your retirement spending, you can enter a lower "desired annual spending" figure representing just the portion you need your savings to cover.
The 4% rule comes from historical U.S. market research (the Trinity Study) testing 30-year retirement periods. It's a widely used starting point, not a guarantee — some planners recommend 3.5% for extra safety margin, especially for retirements longer than 30 years, or adjust it based on market valuations at the time of retirement. Adjust the slider above to see how it changes your numbers.