If you’ve spent time in the FIRE community, you’ve heard about Lean FIRE and Fat FIRE. But Coast FIRE might be the most powerful — and most overlooked — milestone of all.
What Is Coast FIRE?
Coast FIRE is the point at which you’ve saved enough that your portfolio will grow to your full FIRE number on its own, without any additional contributions, assuming a reasonable long-term growth rate.
In other words: you can stop saving for retirement entirely and still retire on time — as long as you cover your current expenses from earned income.
How to Calculate Your Coast FIRE Number
The formula works backwards from your full FIRE number:
Coast FI Number = Full FIRE Number ÷ (1 + growth rate)^years to retirement
For example: if your full FIRE number is $2,000,000, you plan to retire in 25 years, and you assume 7% real returns:
$2,000,000 ÷ (1.07)^25 = ~$370,000
Once you have $370,000 invested and don’t touch it, it will grow to $2M by retirement — even if you contribute nothing else.
Why Coast FIRE Changes Everything
Hitting your Coast FIRE number is transformative because it fundamentally changes the pressure you’re under. At that point, you can:
- Take a lower-paying job you actually enjoy
- Go part-time or freelance
- Take an extended career break
- Work for meaning instead of money
You still need to cover your living expenses — but you’ve removed the need to save aggressively. That’s a form of freedom most people don’t realize is available to them decades before traditional retirement age.
The Catch
Coast FIRE assumes you don’t touch the invested principal. It also depends heavily on your assumed growth rate and time horizon. A longer runway makes the Coast FI number dramatically lower — which is why starting early matters so much more than saving more later.
Modeling your exact Coast FIRE number requires accounting for your current portfolio, expected contributions, target retirement age, and expected expenses at retirement. A multi-year financial model — not a simple calculator — is the right tool for this.