What is Coast FIRE? A plain-English definition
Coast FIRE (sometimes written "Coast FI") is the moment your retirement savings reach a tipping point: you have invested enough that, even if you never contribute another dollar, normal compound growth will grow that money into your full retirement number by the time you actually retire. You still have to pay for today's life — rent, groceries, the occasional flat white — but you no longer have to save a cent for retirement. Your future is, in effect, already funded. From here, you can coast.
That distinction is what makes Coast FIRE so popular on personal-finance forums like Reddit's r/financialindependence and r/coastFIRE. Traditional FIRE (Financial Independence, Retire Early) asks you to accumulate roughly 25 times your annual expenses before you stop working entirely. That is a huge, intimidating number. Coast FIRE reframes the journey: instead of asking "When can I quit forever?", it asks "When can I stop the relentless saving and let time do the heavy lifting?" For most people that milestone arrives years — sometimes a decade — earlier than full FIRE, and it unlocks real options: switching to a lower-stress job, going part-time, taking a sabbatical, or starting a business without the pressure of funding a 401(k) every month.
The engine underneath Coast FIRE is compound interest, and specifically the long runway that younger investors have. A dollar invested at 30 has 35 years to roughly multiply itself several times over before a typical retirement at 65. That is why a 30-year-old might reach Coast FIRE with far less than a 50-year-old needs: the younger saver is buying time, the single most valuable ingredient in compounding.
How the Coast FIRE number is calculated
There are two numbers worth knowing. The first is your full FIRE number — the nest egg you ultimately want. The second is your Coast FIRE number — how much you need invested today so that growth alone reaches that nest egg by retirement.
The formula
Start with your FIRE number. If you plan to spend S per year in retirement and use a withdrawal rate w (the 4% rule means w = 0.04), then:
FIRE number = S ÷ w (for the 4% rule, that's S × 25)
Now discount that target back to the present using your real (inflation-adjusted) rate of return r over the number of years until retirement n:
Coast FIRE number = FIRE number ÷ (1 + r)n
If your current invested assets are already equal to or greater than that Coast FIRE number, congratulations — you have reached Coast FIRE and can, in theory, stop contributing. If not, the gap tells you how much further you have to go, and this calculator estimates the age at which continued contributions will close it.
A worked example
Imagine you are 30, want to retire at 65, and expect to spend $40,000 a year (in today's dollars). Using the 4% rule, your FIRE number is $40,000 × 25 = $1,000,000. Assume a real return of 5% per year after inflation. There are 35 years until retirement, so:
Coast FIRE number = $1,000,000 ÷ (1.05)35 ≈ $1,000,000 ÷ 5.52 ≈ $181,000
In other words, if a 30-year-old can amass about $181,000 and then never invest another dollar, compound growth at 5% real should carry that balance to roughly $1,000,000 by age 65. Everything they earn afterward can go toward living, fun, or working less. Change any input — retire earlier, spend more, assume a lower return — and the Coast FIRE number moves accordingly. That sensitivity is exactly why an interactive calculator beats a static rule of thumb.
Coast FIRE by age: why starting early matters so much
Because compound growth needs time, the single biggest factor in your Coast FIRE number is how many years stand between you and retirement. The earlier you start, the smaller the amount you need invested today — and the gap is dramatic. The table below assumes the same $1,000,000 FIRE target (a $40,000 annual budget at the 4% rule), a 5% real return, and retirement at 65.
- Coast FIRE at 25: with 40 years of growth, you would need roughly $142,000 invested to coast.
- Coast FIRE at 30: with 35 years, about $181,000.
- Coast FIRE at 35: with 30 years, about $231,000.
- Coast FIRE at 40: with 25 years, about $295,000.
- Coast FIRE at 45: with 20 years, about $377,000.
- Coast FIRE at 50: with 15 years, about $481,000.
Notice how the number more than triples between 25 and 50, even though the destination is identical. That is the time value of money in action: a younger investor's dollars simply have more years to double and re-double. A 25-year-old who reaches roughly $142,000 can, in principle, stop contributing entirely and still retire a millionaire (in today's dollars) at 65. Someone who waits until 50 has to bring more than three times as much capital to the table to buy the same outcome, because they have given up the most powerful compounding years.
This is also why personal-finance writers are so insistent that young people invest something, even small amounts, as early as possible. Front-loading your investing — saving aggressively in your twenties and early thirties to hit Coast FIRE quickly — can let you ease off later, precisely when many people face higher expenses from housing, children, or caregiving. The calculator above makes this trade-off concrete: lower your current age or raise your starting balance and watch the Coast FIRE number fall; push retirement earlier and watch it climb. Run a few scenarios and you will quickly develop an intuition for how powerful an extra five years of runway really is.
How to factor inflation into your Coast FIRE number
This is the single most common complaint about low-quality Coast FIRE calculators, and it comes up constantly on Reddit: "Does this thing even account for inflation?" Many do not, and that omission quietly wrecks the result. If a calculator grows your money at a 10% nominal return but never adjusts your target for rising prices, it will tell you that you are far closer to retirement than you really are. A million dollars in 35 years will not buy what a million buys today.
The clean way to handle inflation is to work entirely in today's dollars using a real rate of return. The real return strips inflation out of your nominal return:
real return ≈ (1 + nominal return) ÷ (1 + inflation) − 1
For example, a 7.7% nominal return with 3% inflation is a real return of about 4.6%. A quick-and-dirty version just subtracts (7.7% − 3% = 4.7%), which is close enough for planning. This calculator uses the precise formula and lets you set inflation with a slider, so you can immediately see how a higher-inflation world raises the bar. Because we project in real terms, every figure on the screen — your FIRE number, your Coast FIRE number, the chart — is already expressed in money you understand today. There is no mental gymnastics about what "$2.3 million in 2061" might be worth.
How much inflation should you assume? Central banks in most developed economies target around 2%, and the long-run historical average in the United States is roughly 3%. Many cautious planners use 3% as a baseline and stress-test at 4%. If you live somewhere with structurally higher inflation, raise the slider. The point is not to predict the future precisely; it is to make sure your plan does not silently assume prices stand still.
What investment return should you assume?
Your assumed return is the most powerful lever in the whole calculation, so be deliberately conservative. Over the last century, a broadly diversified US stock portfolio has returned roughly 10% per year nominally, or about 6.5%–7% per year after inflation. A globally diversified portfolio that includes bonds will typically expect less. Because Coast FIRE leans heavily on decades of compounding, even a one-percentage-point difference in assumed return swings the result dramatically.
A few sensible guardrails: prefer real returns in the 4%–6% range for an all-equity portfolio, trim that if you hold significant bonds or cash, and remember that future returns may be lower than the past — valuations, interest rates, and demographics all matter. It is far better to reach Coast FIRE a couple of years "late" because you assumed 4.5% than to coast on a fantasy 9% real return and discover the shortfall at 60. When in doubt, run the calculator twice: once with an optimistic return and once with a pessimistic one, and plan around the gap between them.
Does the 4% rule still apply in 2026?
The "4% rule" comes from the 1990s Trinity Study, which found that a retiree who withdrew 4% of their starting portfolio in year one, then adjusted that dollar amount for inflation each year, had a very high probability of not running out of money over a 30-year retirement. It became shorthand for "you need 25 times your annual expenses." But it was always a guideline, not a law of nature, and three questions decide whether it fits you.
How long is your retirement?
The Trinity Study modeled a 30-year horizon. Someone retiring at 40 might need their money to last 50+ years, which strains the 4% rule. Long horizons are why many in the early-retirement community plan with a 3.25%–3.75% withdrawal rate — equivalent to 27×–31× expenses. This calculator lets you dial the withdrawal rate up or down so you can see exactly how a more conservative rate raises your FIRE number and your Coast FIRE number.
Sequence-of-returns risk
The order of returns matters enormously in the first decade of retirement. A nasty bear market right after you stop working can permanently shrink a portfolio you are simultaneously drawing down — even if average returns over the full retirement look fine. This is "sequence-of-returns risk," and it is the main reason cautious retirees keep a cash buffer, hold some bonds, or stay flexible about spending in down years.
Flexible withdrawal strategies
Modern research (Bengen's later work, the Guyton-Klinger "guardrails," and variable-percentage withdrawal methods) suggests that retirees who are willing to trim spending after bad years can often start higher than 4% and still be safe. The takeaway is not a single magic number but a principle: a static rule is a starting point, and real plans bend with the market. Use the withdrawal-rate slider to find a number you can sleep with, then revisit it as your situation changes.
What about health insurance before Medicare?
For Americans, health insurance is the most underestimated line item in early retirement, and it is a recurring source of anxiety on Coast FIRE threads. Employer coverage usually disappears when you stop working, and Medicare does not begin until age 65. That leaves a gap — potentially decades long for early retirees — that you must fund yourself.
The most common bridge is the ACA marketplace (healthcare.gov or your state exchange). Crucially, marketplace premium subsidies are based on your modified adjusted gross income, not your net worth. Many early retirees deliberately manage their taxable income — living partly from cash and Roth contributions, harvesting capital gains carefully — to qualify for substantial premium tax credits. With planning, a couple can sometimes insure themselves for a few hundred dollars a month rather than the unsubsidized sticker price of well over a thousand.
The practical move for your Coast FIRE math is simple: add an explicit health-insurance estimate to your annual spending figure. If you budget $40,000 a year but expect $9,000 of marketplace premiums and out-of-pocket costs before Medicare, model $49,000 instead. That raises your FIRE number and your Coast FIRE number honestly, rather than leaving a five-figure surprise lurking in your plan. Outside the US, factor in private supplemental coverage or the realities of your national system, but apply the same principle: price healthcare in, don't wish it away.
Coast FIRE vs Barista FIRE vs Lean and Fat FIRE
The FIRE world has a whole vocabulary, and the labels overlap. Coast FIRE means your retirement is fully funded by growth alone, so you only need to earn enough to cover current expenses. Barista FIRE is a close cousin: you work a lighter or part-time job — often for the health benefits, hence the "barista" nickname — that covers some of your living costs while your investments keep compounding. The difference is subtle: Coast FIRE focuses on whether retirement is funded; Barista FIRE focuses on how you bridge current expenses with reduced work.
Lean FIRE describes financial independence on a frugal budget (say, under $40,000 a year), while Fat FIRE describes independence with a comfortable, even luxurious, budget (often $100,000+ a year). These are about the size of the destination; Coast and Barista are about the path. You can absolutely pursue "Coast to Fat FIRE" — reach the coasting point for a generous future budget and then ease off the savings throttle. This calculator works for any of them: set your annual spending to match the lifestyle you are targeting and the math adapts.
How to use this Coast FIRE calculator
Getting an answer takes about thirty seconds:
- Enter your age and target retirement age. The gap between them is your compounding runway — the longer it is, the lower your Coast FIRE number.
- Add your current invested assets. Include retirement accounts (401(k), IRA, pensions you control), taxable brokerage balances, and other long-term investments. Leave out your emergency fund and the equity in the home you live in.
- Set your monthly contribution. This is how much you are currently investing. The calculator uses it to estimate the age at which you will reach Coast FIRE if you keep going at this pace.
- Estimate your annual retirement spending in today's dollars — and remember to include healthcare.
- Tune the sliders: expected annual return, inflation, and your safe withdrawal rate. Watch the chart and the numbers update instantly.
- Read your results. The status banner tells you whether you have already hit Coast FIRE; the cards show your FIRE number, your Coast FIRE number today, the age you can stop saving, and your projected balance at retirement.
- Save or share. Copy a link that encodes all your inputs, or download a clean PDF report to revisit later or discuss with a partner or advisor.
Common Coast FIRE mistakes to avoid
A few errors show up again and again. Ignoring inflation is the biggest — always plan in real terms. Assuming heroic returns is a close second; a 9% real return makes any plan look great on paper and terrible in practice. Forgetting healthcare and taxes understates your true annual spending, which cascades into a Coast FIRE number that is too low. Treating Coast FIRE as the finish line is a mindset trap: it frees you from saving for retirement, but you still need income for today, and life events can change the target. Finally, setting and forgetting is risky — markets, inflation, and your own goals drift, so revisit the calculation once a year and after any big life change. Coast FIRE is a checkpoint, not a guarantee, and the people who benefit most treat it as a living plan rather than a one-time verdict.
Frequently asked questions
What is Coast FIRE in one sentence?
Coast FIRE is having enough invested that compound growth alone will reach your retirement number by your target age, so you no longer need to save for retirement — only cover your current living costs.
Is Coast FIRE realistic, or just internet hype?
It is genuinely realistic, and the math is simply compound interest applied to your own numbers. The catch is that it depends heavily on your assumptions: a sensible return, honest inflation, and complete spending (including healthcare and taxes). Plug in conservative figures and the result is a sound, defensible target rather than wishful thinking.
How is Coast FIRE different from regular FIRE?
Regular FIRE means you have enough to live off your portfolio and never work again. Coast FIRE is an earlier milestone: your retirement is fully funded by future growth, but you still earn enough to pay today's bills. You reach Coast FIRE years before full FIRE.
Does this calculator account for inflation?
Yes. It converts your expected return into a real, inflation-adjusted return and keeps every figure in today's dollars. You control the inflation assumption with a slider, so you can see exactly how rising prices change your Coast FIRE number.
Can I change the 4% rule?
Absolutely. The safe-withdrawal-rate slider lets you choose any rate from 2.5% to 6%. Lower rates (more conservative) raise your FIRE and Coast FIRE numbers; higher rates lower them. Long early-retirement horizons often call for 3.25%–3.75%.
Should I really stop investing once I hit Coast FIRE?
You can, but you do not have to. Many people who reach Coast FIRE keep investing a little to build a buffer, retire even earlier, or upgrade from a lean to a fat retirement. The milestone gives you options; what you do with them is your call.
Is my data private?
Yes. All calculations run entirely in your browser. Nothing you type is sent to a server. The "copy share link" feature simply encodes your inputs into a URL that you choose whether to share.