Coast FIRE Calculator
Coast FIRE is the point where your existing investments, left to compound on their own, will grow to your full FIRE number by traditional retirement age — no further contributions needed. Once you hit Coast FIRE, you only need to earn enough to cover your living expenses. Your retirement savings take care of themselves.
This is one of the most achievable milestones in the FIRE movement. You don't need $1M+ today — you just need enough that compounding can do the rest. A 30-year-old with ~$94K invested at 7% real returns will have $1M by 65 without adding another penny. This calculator finds your personal Coast FIRE number and tells you how close you are.
At age 30 targeting $1,000,000 by 65 at 7% real return, your Coast FIRE number is $93,663. You need $43,663 more to reach Coast FIRE (~$1,093/mo for 3 years).
Formula: Coast FIRE Number = FIRE Number ÷ (1 + r)^years, where r = 7% real return, years = 35
Your numbers
Results
Coast FIRE Number
$93,663
The amount you need today to coast to FIRE
Full FIRE Number
$1,000,000
At age 65 with 4% SWR
Projected at age 65
$533,829
Current savings compounded with no further contributions
Status
$43,663 gap
~$1,093/mo for 3 years to reach Coast FIRE
How to use this calculator
Current age — Your age today. The younger you are, the lower your Coast FIRE number because compounding has more time to work. A 25-year-old needs roughly half the Coast FIRE number of a 35-year-old targeting the same FIRE number.
Target retirement age — The age at which you want your investments to reach your full FIRE number. Traditional retirement is 65, but many FIRE seekers target 50–55. The further out this is, the lower your Coast FIRE number.
Current invested assets — Your total investable assets: 401(k), IRA, brokerage, HSA. Don't include your home equity unless you plan to sell and invest it. This is the balance that will compound on its own.
Expected real return — Your after-inflation annual return. 7% is a common assumption for a stock-heavy portfolio based on S&P 500 history. Use 5% for a more conservative estimate with bonds mixed in.
Annual expenses in retirement — What you expect to spend yearly once retired. Start with current spending and adjust for paid-off mortgages, healthcare, etc. This determines your full FIRE number.
Safe withdrawal rate — The percentage you'll withdraw annually. 4% is the classic rule. Use 3.5% for extra safety, especially for early retirees with 40+ year horizons.
Real-world examples
Age 25 with $50K saved, targeting $1M by 65
At 7% real return over 40 years, the Coast FIRE number is ~$66,800. With $50K saved, they're already 75% of the way there. Just $16,800 more and they never need to save for retirement again. This is why starting early is so powerful.
Age 35 with $100K saved, targeting $1.25M by 60
At 7% over 25 years, the Coast FIRE number is ~$230,000. With $100K saved, they need ~$130K more. At $2,000/month contributions, they reach Coast FIRE in about 5 years — then they can switch to lower-stress work and just cover living expenses.
Age 40 with $200K saved, targeting $800K by 55
At 7% over 15 years, the Coast FIRE number is ~$289,000. They need ~$89K more. At $2,500/month, they hit Coast FIRE in about 2.5 years. After that, they could take a lower-paying job they love and still retire at 55.
Formula & Methodology
Coast FIRE Number formula
- FIRE Number = Annual Expenses ÷ Withdrawal Rate
- r = Expected real annual return (e.g., 0.07 for 7%)
- years = Target retirement age - Current age
How it works
The formula reverses the compound interest calculation. Instead of asking "what will my money grow to?", it asks "how much do I need today so that compounding alone gets me to my FIRE number?" The longer the time horizon, the less you need today — because compounding has more time to work its magic.
Assumptions & limitations
- Returns are assumed constant. Real markets fluctuate significantly year to year.
- Inflation is not modeled separately — use real returns (~7%) for inflation-adjusted projections.
- Does not account for taxes on investment gains in taxable accounts.
- After reaching Coast FIRE, you still need to earn enough to cover living expenses — just not save for retirement.