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Coast FIRE Calculator: When You Can Stop Saving

Use this Coast FIRE calculator to find the milestone where you can stop saving and let compounding do the work. Enter your retirement target and current age to see the dollar amount you need invested today.

$
yrs
yrs
%
$
Coast FIRE number (today)$0
Years to coast0
Gap (or surplus)$0
% of way there0.00%
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How this calculator works

Coast FIRE inverts the standard retirement-projection question. Instead of "how much should I save monthly to hit my number?" it asks: "how much do I need invested today so that compounding alone — zero further contributions — gets me there?"

coast = target / (1 + r)years
target
Your retirement portfolio goal. Default uses the 4% rule: 25× expected annual spending. So $60K/yr × 25 = $1.5M.
r
Expected real (inflation-adjusted) return. 7% is the long-term S&P average; use 5% for conservative.
years
Years until target retirement age

If your current portfolio ≥ the coast number, you've hit Coast FIRE — your remaining job income covers living expenses, but compounding alone funds retirement. You're free to switch to lower-stress work, take sabbaticals, or just stop stressing about saving rates.

Source: The 4% rule originated in the Trinity Study (1998). Real long-term U.S. equity returns — Federal Reserve Economic Research.

FAQ

What's the difference between Coast FIRE and regular FIRE?
Regular FIRE means you have enough to retire now — your portfolio funds your spending forever. Coast FIRE means you have enough that you no longer need to save more to retire on time — but you still need to earn enough to cover today's expenses until then. Coast FIRE is reached much earlier than full FIRE.
Is the 4% rule still valid?
It's a planning starting point, not a guarantee. Recent research (Big ERN, Bengen 2020) suggests 4% is reasonable for a 30-year retirement starting in normal markets, but 3.0–3.5% may be safer for early retirees with 50+ year horizons. To be conservative, multiply your annual spend by 30 instead of 25.
Should I really stop saving once I hit Coast FIRE?
You don't have to. Continuing to save buys you flexibility: earlier retirement, higher spend, larger inheritance, or a bigger margin against bad market sequences. Many Coast-FIRErs keep saving 10–15% but switch to less stressful work. Coast FIRE is permission to stop, not an obligation.
What is the difference between Coast FIRE and Lean / Fat FIRE?
Lean FIRE = retire on minimal expenses (<$40K/year); Fat FIRE = retire on luxury spending ($100K+/year); Coast FIRE = you have enough invested NOW that compounding alone gets you to retirement, but you still need current income for today's expenses. Coast lets you switch to lower-stress work without saving more.
How is the Coast FIRE number calculated?
It is the present value of your retirement target, discounted by your real return. coast = target / (1 + r)years. With a $1.5M target, 7% real return, and 35 years to retirement, you need ~$140K invested today and zero further contributions to land at $1.5M.
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