Coast FIRE Calculator
Coast FIRE is the halfway milestone: the point where your savings are big enough to grow into your retirement number on their own — no more contributions needed. Find your coast age below.
Your inputs
Coasting trajectory: stop contributing, let it grow
The verdict
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What is Coast FIRE?
Coast FIRE is the point where you've saved enough that, even if you never contribute another dollar, compounding alone will grow your portfolio to your full retirement number by the time you retire. After coasting age, your only job is to cover your current living expenses — retirement funding runs on autopilot.
It's psychologically powerful: full FIRE can feel impossibly far away, but Coast FIRE often arrives a decade earlier. Many people hit it and downshift — less overtime, a lower-paying but happier job, more time with family — knowing the retirement math already works.
The math behind this calculator
Your FI number is 25× your annual retirement spending. Then we ask: how many years of compounding does your current savings need to reach it?
Coast age = retirement age − years needed
If the years needed are fewer than the years until retirement, you've already coasted. If more, the calculator shows how much you'd need saved today to coast: FI number ÷ (1 + r)years until retirement.
Worked example
You're 32 with $150,000 saved, plan to retire at 60, expect 7% returns, and will spend $60,000/year in retirement (FI number: $1.5M). Years needed = ln(1,500,000 ÷ 150,000) ÷ ln(1.07) ≈ 34. Years until retirement: 28. Since 34 > 28, you're not coasting yet — you'd need about $226,000 saved today to coast. But notice how close it is: every extra dollar saved now does 28 years of compounding.
Caveats worth knowing
- "No contributions" is the optimistic case. Job losses, emergencies, or lifestyle creep can raid the portfolio. Coast FIRE assumes the money stays invested and untouched.
- Returns are assumed constant at r%. A market crash right after you stop contributing hurts far more than the smooth average suggests.
- The 25× target has the same limits as the 4% rule — it's built for ~30-year retirements. Retiring at 60 and living to 95 is 35 years; consider a margin of safety.
- Inflation matters. Your FI number is in today's dollars; in practice, both your spending target and returns should be thought of in real (inflation-adjusted) terms.
Background: the 25× framework comes from financial planner William Bengen's 1994 research on sustainable withdrawal rates; see also our 4% rule calculator.