Calculator
Coast FIRE Calculator
Your Coast FIRE number is the amount you need saved today so that compound growth alone reaches your full FIRE number by retirement — no more contributions required.
Your numbers
How much you plan to spend per year
$
4.0%
2% (conservative)6% (aggressive)
7.0%
Inflation-adjusted annual return
3%12%
For timeline calculation
$
$
Your Coast FIRE Number
—
Full FIRE number
—
Years of runway
—
Discount factor
—
Progress to Coast FIRE 0%
$0 saved — needed
Timeline
—
years to coast
—
coasting age
—
est. at retirement
Coasting age explorer
How your portfolio and the required coast number compare at each age milestone
| Age | Coast number needed | Gap / Surplus |
|---|
How it works
The math behind Coast FIRE
1
Enter your annual retirement expenses
How much do you plan to spend per year in retirement? This drives your full FIRE number, which the Coast number is derived from.
2
Set your safe withdrawal rate
Defaults to 4%. Use 3–3.5% for very long retirements. This determines your full FIRE number.
3
Enter your current and retirement ages
The gap between these two ages is the runway your investments have to grow. A longer runway means a smaller Coast FIRE number today.
4
Set the expected real return
The annual return your portfolio is expected to earn, adjusted for inflation. 7% is the historical average for a diversified index fund portfolio.
5
Add your current savings and contribution
Your current savings shows how close you are to the Coast number. Your annual contribution determines how quickly you get there.
Coast FIRE formula
Coast = FIRE Number ÷ (1 + r)^n n = years until retirement · r = annual real return
Example
$1.25M ÷ (1.07)^35 = $130,320 $1.25M FIRE number · 7% return · 35 years runway
Frequently asked questions
What is Coast FIRE?
Coast FIRE is the point at which your invested assets will grow to your full FIRE number by traditional retirement age — without ever investing another dollar. Once you hit your Coast FIRE number, you only need to earn enough to cover current living expenses. No more aggressive saving required.
How is the Coast FIRE number calculated?
Coast FIRE Number = FIRE Number ÷ (1 + r)^n, where r is your expected annual real return and n is the number of years until your target retirement age. The further away retirement is, the smaller the Coast number — because compound interest has more time to do the work.
What happens after I reach Coast FIRE?
You can stop making investment contributions and simply let your existing portfolio grow. You still need to earn enough to cover your current living expenses — but you no longer need to save aggressively. Many people use this milestone to shift to lower-stress work, part-time employment, or pursue a passion project.
Is Coast FIRE risky if markets underperform?
It carries more sequence-of-returns risk than continuing to contribute, since you are relying entirely on growth. Building a small buffer above the calculated Coast FIRE number (say, 10–20%) before stopping contributions is a common risk mitigation strategy. Continuing to save even a small amount also helps.
Can I use a retirement age younger than 65 for Coast FIRE?
Yes. Coast FIRE is flexible about the target retirement age. If you plan to fully retire at 50 instead of 65, your Coast FIRE number will be higher (less time for compound growth). Many people calculate multiple Coast numbers — one for age 50, one for 60, one for 65 — to understand the tradeoffs.