Enter your numbers
The age your portfolio must reach full FIRE by.
In today's dollars. This sets your FIRE number.
After inflation. 7% is the long run US stock market average.
4% is the classic rule. Lower is more conservative.
Your Coast FIRE results
Your trajectory vs the Coast line
Year by year projection
| Age | Your balance | Coast number at that age | Gap |
|---|
Balances assume zero new contributions and a constant real return. The Coast number at each age is the FIRE number discounted back at the same return. Where your balance meets the Coast line is your Coast age.
The math behind Coast FIRE
Coast FIRE answers one question: what lump sum today, with no further contributions, grows into your full retirement number by your target age? That is a present value calculation.
Where:
- FIRE number = annual retirement spending ÷ withdrawal rate. At a 4% withdrawal rate this is the familiar 25× rule.
- r = expected real (after inflation) annual return, so everything is in today's dollars.
- n = years from your current age to your target retirement age.
Example: $60,000 of annual spending at a 4% withdrawal rate gives a $1,500,000 FIRE number. A 35 year old retiring at 65 with a 7% real return has n = 30, so the Coast number is $1,500,000 ÷ 1.0730 ≈ $197,000. With $197,000 invested at 35 and no new contributions, compounding alone delivers $1,500,000 by 65.
Assumptions this calculator uses: returns are constant real returns with no sequence of returns risk; amounts are in today's dollars; annual spending never changes; no taxes, fees, pensions, or Social Security; contributions stop at the Coast number; the withdrawal rate funds spending forever.
Coast FIRE vs Lean FIRE vs Fat FIRE
- Coast FIRE means you have saved enough early that compounding alone reaches your full retirement number by traditional retirement age. You keep working, but retirement saving becomes optional. You only need to cover current living expenses.
- Lean FIRE means retiring early on a minimalist budget. The FIRE number is smaller because spending is smaller, so it can be reached sooner, but it requires real lifestyle cuts that last.
- Fat FIRE means retiring early with a generous lifestyle. The FIRE number is much larger, so it takes far longer to save, but retirement spending is high and flexible.
- Standard FIRE is the middle path: save about 25× annual spending and stop working entirely once you get there.
Coast FIRE is different from the other three because it is not a retirement date. It is the moment your investments go on autopilot. Lean, Fat, and standard FIRE all describe when you stop working. Coast FIRE describes when you can stop saving.
Coast FIRE FAQs
What does it mean to be Coast FIRE?
It means your current invested savings will grow, with no further contributions, into your full FIRE number by your target retirement age. You still work and cover your bills, but you no longer need to direct income into retirement accounts.
How is the Coast FIRE number calculated?
First compute the traditional FIRE number: annual retirement spending divided by your withdrawal rate. Then discount that number back from your target retirement age to your current age at your expected real return: FIRE number ÷ (1 + real return)years remaining.
What is a good real return to assume?
7% per year is the commonly used long run real return for a US stock heavy portfolio, after inflation. If you hold more bonds or want to be conservative, 5% or 6% is reasonable. A lower return assumption raises your Coast number, which is the safer direction.
Can I stop contributing entirely once I hit my Coast number?
In theory yes, that is the definition of Coast FIRE. In practice many people keep contributing for a margin of safety, because real returns vary and spending plans change. Treat the Coast number as a milestone, not a guarantee.
What if my savings are already above my Coast number?
You are already Coast FIRE. The calculator will show 0 years until Coast and tell you the age at which you hit it. Every dollar above the line shortens nothing about the math, it just adds a buffer.
Does Coast FIRE account for inflation?
Yes, by using a real (after inflation) return rate. Because both the growth and the discounting use real returns, all dollar figures are in today's dollars. Your nominal account balance will be higher, but its purchasing power matches the numbers shown.