What is Coast FIRE?
Coast FIRE (Financial Independence, Retire Early) is the milestone where the money you've already invested is enough — all by itself — to grow into your full retirement nest egg by your target retirement age. Once you reach Coast FIRE, you never have to save another dollar for retirement. You still work to pay your current bills, but the pressure to save disappears: compound growth is now doing the heavy lifting.
The concept builds on the famous 4% rule, derived from the Trinity Study. It says you can retire once your portfolio equals roughly 25 times your annual spending, because a diversified portfolio has historically supported 4% annual withdrawals for 30+ years. So if you plan to spend $40,000 per year in retirement, your FIRE number is $1,000,000. Coast FIRE simply asks: how much would I need invested today for that $1,000,000 to appear on its own by the time I retire?
Because compounding is exponential, the answer is often shockingly small for young savers. A 25-year-old needs around $218,000 invested to "coast" to a $1 million retirement at 65, while a 50-year-old needs more than half a million. That's why your Coast FIRE number is one of the most motivating metrics in personal finance — it converts a vague, decades-long goal into a single, concrete balance you can track your progress against.
How to Use This Coast FIRE Calculator
Six quick steps — click any step to jump straight to that field in the calculator above.
Coast FIRE Formula
The Coast FIRE formula combines two steps:
FIRE Number = Annual Spending ÷ Safe Withdrawal Rate
Coast FIRE Number = FIRE Number ÷ (1 + r)years
where r = real return = (1 + nominal return) ÷ (1 + inflation) − 1
Worked example
Meet Alex: age 30, wants to retire at 60, plans to spend $40,000/year, assumes 7% returns, 3% inflation, and a 4% withdrawal rate.
- Real return: (1.07 ÷ 1.03) − 1 = 3.88%
- FIRE number: $40,000 ÷ 0.04 = $1,000,000
- Years of growth: 60 − 30 = 30 years
- Coast FIRE number: $1,000,000 ÷ 1.038830 ≈ $319,000
If Alex already has $319,000 invested at 30, retirement at 60 is funded even with $0 in future contributions. If Alex has less — say $150,000 — the calculator shows exactly when continued monthly investing crosses the coast line, and what monthly contribution would close the gap.
Coast FIRE vs Barista FIRE vs Lean FIRE vs Fat FIRE
| Type | What it means | Do you still work? | Portfolio needed |
|---|---|---|---|
| Coast FIRE | Investments grow untouched to fund retirement at a traditional age | Yes — covers current expenses only | Lowest (grows on its own) |
| Barista FIRE | Part-time work supplements early, small portfolio withdrawals | Yes — part-time, often for benefits | Low–medium |
| Lean FIRE | Full retirement on a frugal budget (typically under $40k/yr) | No | Medium (small spending) |
| Fat FIRE | Full retirement with a luxurious lifestyle ($100k+/yr) | No | Highest ($2.5M+) |
Coast FIRE is the most accessible flavor of financial independence because it doesn't require a huge portfolio — it requires time. It's a perfect intermediate milestone on the road to full FIRE: hitting it proves your retirement is on track and buys you enormous career flexibility decades before you actually retire.
Coast FIRE Number by Age
Here's what you need invested at each age to coast to a $1,000,000 retirement at 65 ($40,000/year spending, 7% nominal return, 3% inflation, 4% withdrawal rate):
| Age | Coast FIRE number | Details |
|---|---|---|
| 25 | $217,840 | Coast FIRE at 25 → |
| 30 | $263,555 | Coast FIRE at 30 → |
| 35 | $318,862 | Coast FIRE at 35 → |
| 40 | $385,777 | Coast FIRE at 40 → |
| 45 | $466,733 | Coast FIRE at 45 → |
| 50 | $564,679 | Coast FIRE at 50 → |
Notice the pattern: every five years you wait, the required balance roughly increases by about 20–25%. That's the cost of lost compounding time — and the best argument for investing early, even in small amounts. Explore every age from 20 to 65 on our Coast FIRE by age pages.
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Frequently Asked Questions
What is Coast FIRE? +
Coast FIRE is the point where you have enough invested that, without adding another dollar, your portfolio will grow to fund your retirement by your target retirement age. Once you "coast", you only need to earn enough to cover your current living expenses — compound growth handles the rest.
How is the Coast FIRE number calculated? +
First find your FIRE number: annual retirement spending divided by your safe withdrawal rate (e.g. $40,000 ÷ 4% = $1,000,000). Then discount it back to today using your real (inflation-adjusted) return: Coast FIRE Number = FIRE Number ÷ (1 + real return)^years until retirement.
What is a good safe withdrawal rate? +
The classic "4% rule" comes from the Trinity Study and is the most common assumption. If you plan a very long retirement (40+ years) or want extra safety, many planners use 3.25–3.5%, which raises the portfolio you need.
Should I use nominal or real returns? +
This calculator works in real (today's) dollars: it converts your nominal return into a real return using real return = (1 + nominal) ÷ (1 + inflation) − 1. That way your retirement spending target stays in today's purchasing power and you don't have to adjust for inflation yourself.
What happens after I reach Coast FIRE? +
You can stop contributing to retirement accounts entirely if you want. You still need income to cover current expenses — many people switch to lower-stress or part-time work (similar to Barista FIRE) — but your retirement is mathematically funded as long as markets deliver roughly the assumed returns.
How is Coast FIRE different from Barista FIRE? +
In Coast FIRE your investments are left completely untouched to grow until traditional retirement age, and work only covers your day-to-day spending. In Barista FIRE you typically withdraw from your portfolio early and use part-time work (often for health insurance) to supplement smaller withdrawals.
Is Coast FIRE realistic with average returns? +
It depends on time. Because compound growth is exponential, young savers need surprisingly little: about $218,000 invested at age 25 (assuming $40k spending, 7% return, 3% inflation, 4% SWR, retiring at 65) can grow into a full $1,000,000 retirement portfolio. The later you start, the larger the required balance.
Does this calculator account for taxes or Social Security? +
No. It is a simplified educational model using constant real returns and does not model taxes, Social Security, pensions, or market volatility. Treat results as a planning estimate, not a guarantee, and consult a financial professional for personalized advice.
What does a Coast FIRE calculator tell you? +
A Coast FIRE calculator tells you the exact amount you need invested today so that compound growth alone can fund your retirement — without any further contributions. It also shows whether you have already reached that point, the age you will reach it at your current savings rate, and how your portfolio is projected to grow versus the target.
Is this the best coast FIRE calculator? +
We built it to be. Unlike most coast FIRE calculators, results update in real time as you type (no calculate button), the interactive chart lets you hover any year to see exact values, and it marks the precise point your portfolio crosses the coast line. It is completely free, has no sign-up, no ads, and works fully on mobile.
How does this coast FIRE calculator help with retirement planning? +
It turns a vague goal — “retire comfortably” — into one concrete number to track. You can test how retiring earlier, spending less, or investing more changes your coast age, and see the monthly contribution needed if you are not yet on track. Many people check in a few times a year to confirm they are still on course.
Can I use this coast FIRE calculator for couples? +
Yes. Combine both partners' invested assets (all 401(k)s, IRAs, and brokerage accounts), use your household annual retirement spending, and enter your combined monthly contribution. For age gaps, a common approach is to plan around the age at which the older partner wants to retire. Read our Coast FIRE for couples guide in the blog for a full worked example.
How do I use this coast FIRE calculator with Social Security? +
Subtract your expected annual Social Security benefit from your annual retirement spending, and enter only the remainder as spending. For example, if you plan to spend $40,000 and expect $24,000 from Social Security, enter $16,000. Keep in mind benefits usually start at 62–70, so your portfolio must bridge the gap years before they begin. Our blog guide on Coast FIRE with Social Security walks through the full math.
Can I use this coast FIRE calculator with a pension? +
Yes — treat the pension like Social Security: subtract the expected annual pension income from your retirement spending and enter the remaining amount. Note whether your pension has a cost-of-living adjustment (COLA); a fixed pension loses real value to inflation, so be more conservative. See the pension guide on our blog for a worked example.
Want the full story?
Read our in-depth guide: What is Coast FIRE? The Complete Guide — or scroll back up and plug your real numbers into the Coast FIRE calculator.