This site’s FIRE calculator finds the number you need to retire on and how long reaching it takes if you keep contributing. Coast FIRE asks a narrower, often more useful question: what’s the smallest amount I’d need invested right now such that growth alone — with zero further contributions — gets me there?
How it works
The full FIRE number uses the same 25× annual-expenses rule (the inverse of a 4% withdrawal rate) documented on this site’s FIRE calculator. This calculator discounts that target backward, using ordinary compound-interest math, to find what would have to be invested today to reach it purely through investment growth by your target age. It then compares that “coast number” against what you actually have saved.
Why this is a different number than the FIRE calculator gives
Reaching a $1,000,000 FIRE number in 25 years at a 7% return doesn’t require $1,000,000 worth of contributions — it requires about $184,000 invested today and left alone, because $184,000 compounded at 7% for 25 years grows to roughly $1,000,000 on its own. Once someone has that “coast number” invested, every additional contribution is optional rather than required — they can stop saving for retirement specifically and still arrive on schedule, which is the entire appeal of the concept.
What this does not include
This assumes a constant annual return for the entire period, which real markets never actually deliver — a real portfolio’s path is uneven even when its long-run average matches the rate entered here. It also doesn’t account for inflation eroding the real value of a fixed future dollar target, or for taxes on investment growth along the way. And like the FIRE calculator it borrows its 25× figure from, the 4% rule behind it is a historical observation over one dataset, not a guarantee.
How to use this calculator
- Enter your expected annual expenses in retirement — this sets your full FIRE number.
- Enter what you have invested today and how many years until your target retirement age.
- Enter an expected annual return; the calculator shows your coast number and whether your current savings already clear it.
Frequently asked questions
Does Coast FIRE mean I can stop working entirely?
No — it means you could stop contributing toward retirement specifically and your invested savings would still reach your FIRE number through growth alone. Most people using this concept keep working to cover current living expenses, just without also needing to save for retirement.
What if my current savings are already above the coast number?
The gap shown turns negative, reported here as a surplus — you’re already past the point where continued contributions are mathematically required to hit your target, though nothing stops you from adding more.
Why does a lower expected return raise the coast number?
A lower return compounds your current savings less over the same stretch of years, so a larger starting balance is needed to still land on the same target — the coast number and the assumed return move in opposite directions.
Is this the same as the FIRE calculator on this site?
No — the FIRE calculator answers what to save toward and how fast with continued contributions; this one answers the smaller number needed today to stop contributing altogether and still arrive through growth alone.
