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Investing & Retirement
Coast FIRE Calculator — When You Can Stop Saving for Retirement
The point where compound growth alone carries you to retirement — no new savings required
Coast FIRE answers one specific question: can I stop contributing to retirement right now and still retire on schedule? It's not about projecting a balance or maxing an account — it's a yes/no milestone. The moment your existing investments are large enough that compound growth by itself will reach your full retirement target by your chosen age, you've hit Coast FIRE. You keep working to pay today's rent and groceries, but every future paycheck is freed from the retirement-savings obligation. Your nest egg simply "coasts" the rest of the way on its own.
The calculation works backwards from a future goal, which is what sets it apart from a forward-looking savings projection. Instead of asking "how big will my deposits grow?", Coast FIRE asks "how small can today's balance be and still arrive on time with no deposits at all?" That makes it a discounting problem — taking a future dollar amount and pulling it back to its present-day equivalent.
Two inputs feed it. Your FIRE number is the full retirement nest egg, sized by the 4% rule: if a portfolio can sustainably pay out about 4% a year, you need roughly 25× your annual retirement spending. Plan to spend $40,000/year in retirement and your FIRE number is about $1,000,000. Your real return is the inflation-adjusted growth rate that bridges today to retirement. The Coast FIRE number is then the FIRE number discounted back across the years you have left:
Coast FIRE number = FIRE number ÷ (1 + r)ⁿ
Worked example. You're 30, aiming to retire at 60, expecting a 7% real return, planning $40,000/year of spending. FIRE number: 40,000 × 25 = $1,000,000. With 30 years of runway the growth factor is 1.07³⁰ ≈ 7.612, so your Coast FIRE number is 1,000,000 ÷ 7.612 ≈ $131,367. Hit that balance today and you could literally never deposit another dollar yet still land at $1,000,000 by 60. Sitting at $90,000 instead? You're roughly $41,000 short of coasting — close, but not there yet.
Why this number lives or dies on the real return. Because the 4%-rule target is expressed in today's purchasing power, the growth rate you discount with must be inflation-adjusted too. Mixing a 10% headline return into a target sized in today's dollars is a category error: it shrinks the Coast FIRE number on paper and tricks you into declaring victory years early. A stock-heavy portfolio's real return has historically run nearer 6–7% once inflation is stripped out — pair like with like and the milestone tells the truth. If you instead want to project a balance forward from ongoing deposits, that's a job for a compound interest calculator; if you want to model employer-matched paycheck saving, reach for a 401(k) calculator. Coast FIRE deliberately assumes zero new contributions — that's the whole point.
This tool provides informational estimates only, not financial advice; real returns, inflation, and safe withdrawal rates vary, and your results aren't guaranteed.
Calculator
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📰 Formula
• FIRE number = annual retirement spending × 25 (the 4% rule) • Years to grow n = retirement age − current age • Growth factor = (1 + real return ÷ 100)ⁿ • Coast FIRE number = FIRE number ÷ growth factor • Gap = Coast FIRE number − current invested assets (positive = short, negative = surplus)
📰 Formula
• FIRE number = annual retirement spending × 25 (the 4% rule) • Years to grow n = retirement age − current age • Growth factor = (1 + real return ÷ 100)ⁿ • Coast FIRE number = FIRE number ÷ growth factor • Gap = Coast FIRE number − current invested assets (positive = short, negative = surplus)
🧪 Worked examples
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Example 2
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Example 3
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Example 4
⚠️ Common mistakes
- Using a nominal return (10%) instead of a real, inflation-adjusted return (6–7%).
- Forgetting that the FIRE number is spending × 25, not just one year of spending.
- Counting cash, home equity or a paid-off car as part of invested assets — use only investments.
- Treating Coast FIRE as permanent when your spending target or retirement age changes.
💡 Tips
- Use a real (inflation-adjusted) return — historically about 6–7% for a stock-heavy portfolio.
- Coasting only works if you keep covering today's expenses so you never tap the portfolio early.
- Re-run the number every year or two; a higher spending target raises the bar you must clear.
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❓ Frequently asked questions
What is Coast FIRE?
Coast FIRE is the point where you've invested enough that compound growth alone will reach your full retirement number by your target age — so you can stop contributing to retirement accounts. You still work to pay current bills, but you no longer need to save for retirement.
How is the Coast FIRE number calculated?
It's a discounting calculation — a future target pulled back to today. Take your FIRE number (annual spending × 25) and divide by the growth factor (1 + real return) raised to the years until retirement. Example: a $1,000,000 FIRE number, 30 years out at a 7% real return, divided by 1.07³⁰ (7.612) ≈ $131,367 you'd need invested right now. Hit that and growth alone finishes the job.
What is the difference between Coast FIRE and regular FIRE?
Regular FIRE means you have the full nest egg (about 25× spending) and can stop working entirely. Coast FIRE means you have enough invested that you can stop saving, but you still work to cover living expenses until your money grows to the FIRE number.
Why must I use a real return instead of a nominal one?
Because Coast FIRE discounts a future target back to today, and that target is already in today's purchasing power. To pull it back correctly the growth rate has to be in the same units — inflation-adjusted. A stock-heavy portfolio has historically grown about 6–7% in real terms. Feed in a 10% nominal rate and you'll discount too aggressively, shrinking the balance you 'need' today and coasting before you actually can.
Why is the FIRE number 25 times spending?
It comes from the 4% rule: if you withdraw 4% of your portfolio per year, the portfolio is 1 ÷ 0.04 = 25 times your annual spending. So $40,000 of spending implies a $1,000,000 target. Some planners use 3.5% (≈28×) for a more conservative cushion.
What balance counts toward the Coast FIRE test?
Only money that will compound at your assumed real return until retirement — your 401(k), traditional and Roth IRA, taxable brokerage, and similar long-horizon investments. Leave out your emergency fund, checking balance, primary-home equity, and vehicles. Those either won't grow at the return you discounted with or you can't tap them for retirement, so counting them would falsely declare you've coasted. If you want to project any one of those accounts forward on its own, a 401(k) or Roth IRA calculator is the better fit; Coast FIRE only checks the combined invested total against the discounted target.
Do I have to stop saving once I hit Coast FIRE?
No — that's the key distinction. Coast FIRE only tells you that you *could* stop contributing and still arrive on time; it doesn't say you must. Plenty of people keep saving to retire earlier, pad their cushion, or fund a bigger future lifestyle. The milestone hands you optionality — the freedom to redirect cash to a house, a sabbatical, or paying off debt without derailing retirement.
What happens if my returns come in lower than I assumed?
A lower real return makes the growth factor smaller, which pushes your Coast FIRE number higher — your money has less lift to do the same job. So a balance that looked like 'coasted' at 7% might be short at 5%. If markets underperform, you may have to resume contributing to get back on track. Re-running with a deliberately conservative return shows the more defensive balance you'd want before you stop saving for good.
Once I've hit Coast FIRE, is the decision locked in?
No — it's a snapshot, not a guarantee. The number assumes your spending target, retirement age, and real return all hold. Raise your future lifestyle, retire earlier, or hit a weak market decade and the bar moves. Treat Coast FIRE as a green light to stop saving *if nothing major changes*, and re-test it every year or two. The further you are from retirement, the more a small drift in assumptions shifts the discounted target.