Coast FIRE is the point where compounding takes over: invested assets that will grow into a full retirement without another dollar added. Find your number and your gap.
The milestone before the milestone
Full financial independence takes most people decades. Coast FIRE is the earlier, stranger milestone: the day your invested assets are projected to finish the job on their own. Every dollar invested young works longer than a dollar invested later — Coast FIRE is where those early dollars, compounded to your retirement age, cover the whole target.
The formula
- FI number = annual retirement spending ÷ safe withdrawal rate
- Coast number = FI number ÷ (1 + real return)^(years until retirement)
- You've reached Coast FIRE when your invested assets ≥ your Coast number.
How to use the result
The gap to your Coast number is the most motivating figure in personal finance: it shrinks from both sides, as you save and as time passes. Knowing it changes decisions — how hard to push savings now, whether a lower-paying job you'd love is affordable, when downshifting becomes possible. Revisit yearly with updated balances and assumptions; it's a projection, not a promise.
Frequently asked questions
- What is Coast FIRE, exactly?
- It's the point where your existing investments, left completely untouched, are projected to grow into a full retirement fund by your target age. After that point you only need to earn enough to cover current living costs — retirement saving itself is optionally done.
- Why use a real (after-inflation) return?
- Because your retirement spending is entered in today's dollars. Using an inflation-adjusted return keeps both sides of the equation in the same units, so the projection means what it appears to mean. A common approach is to subtract expected inflation from your nominal return assumption.
- Is the 4% withdrawal rate safe?
- It's a research-derived rule of thumb, not a guarantee — based on historical US market data over 30-year retirements. Longer retirements and more cautious assumptions argue for 3–3.5%. Try both in the calculator; the Coast number is quite sensitive to it.
- I've hit my Coast number. Should I actually stop saving?
- Reaching Coast FIRE means you could — it doesn't mean you must. The projection assumes decades of average returns that markets won't deliver smoothly. Many people keep saving at a relaxed pace and treat the milestone as what it really is: the point where work becomes more of a choice.