Coast FIRE Calculator
Find out how much you need saved today so compound growth alone reaches your FIRE number — no further contributions required. All calculations happen locally — nothing leaves your browser.
What is Coast FIRE? Coast FIRE is the portfolio balance at which compound growth alone reaches your full retirement number by your target age, with no further contributions. It is your FIRE number discounted back to today at your real return: Coast Number = FIRE Number ÷ (1 + real return)years. Reaching it does not mean you stop working — it means you stop saving for retirement and only need to cover current living costs.
How to Use the Coast FIRE Calculator
- Enter your current and target age — The gap between the two is the compounding runway. Target age is when you want the portfolio to be fully funded — often 60 or 65 rather than an early-retirement date, because Coast FIRE deliberately leans on a long horizon.
- Enter what you have invested today — Count retirement accounts and taxable brokerage balances — money that is actually invested and will compound. Cash held for an emergency fund or a house deposit is not part of this figure.
- Set your annual retirement expenses — This drives everything downstream. Use today's spending in today's dollars, then subtract costs that end at retirement (a mortgage that will be paid off, commuting) and add ones that start, such as buying your own health cover.
- Adjust the return, inflation and withdrawal assumptions — The calculator converts your nominal return into a real return using the inflation figure, so the result stays in today's money. The withdrawal rate turns expenses into the full FIRE number — 4% implies 25× expenses, 3.5% implies about 28.6×.
- Read the Coast number and the progress bar — The headline figure is what you need invested right now. The bar shows your current balance as a share of it, and the subtitle estimates how long your current contributions take to close the gap.
- Add an annual contribution to see the gap close — Leave contributions at 0 to answer "am I there yet?". Enter a realistic yearly figure to see how many years of saving remain before you can stop — the dashed grey line on the chart shows that faster path.
How the Coast FIRE Calculation Works
Coast FIRE is compound interest run backwards. Instead of asking how big a portfolio grows to, it asks how small it can be today and still land on target. The calculation takes three steps, and every one of them is visible in the inputs above.
First the tool turns your retirement spending into a full FIRE number by dividing annual expenses by the safe withdrawal rate:
FIRE Number = Annual Expenses ÷ Withdrawal RateAt $40,000 of annual spending and a 4% withdrawal rate that is $1,000,000 — the familiar "25 times expenses" rule expressed as a division rather than a multiplication. Lower the withdrawal rate to 3.5% and the same spending needs about $1,143,000, because a more cautious rate demands a bigger portfolio.
Second, it converts your nominal return into a real return using the Fisher relationship rather than simply subtracting inflation:
Real Return = (1 + nominal) ÷ (1 + inflation) − 1A 7% return with 3% inflation gives 1.07 ÷ 1.03 − 1 = 3.88%, not the 4.00% you get by subtracting. The gap is small over one year and material over thirty, which is exactly the horizon this tool works on. Using the real return also means every dollar figure on the page stays in today's money, so a Coast number of $264,000 is comparable to the $264,000 in your account right now.
Third, it discounts the FIRE number back across the years remaining until your target age:
Coast Number = FIRE Number ÷ (1 + real return)yearsA worked example
Take the defaults on the page: age 30, target age 65, $40,000 of retirement spending, a 4% withdrawal rate, 7% returns and 3% inflation. The FIRE number is $1,000,000. The real return is 3.88%, and there are 35 years of runway, so the discount factor is 1.038835 ≈ 3.79. Dividing gives a Coast number of roughly $264,000. Someone with $150,000 invested is about 57% of the way there — the progress bar reads the same figure.
When your balance already exceeds the Coast number, the tool says so directly and reports zero years to coast. When it does not, it solves for the number of years your current contributions need to close the gap, using the same annuity-growth formula a savings calculator uses. If the contribution is zero and the balance is short, growth alone still closes the gap eventually, because the Coast number is a fixed target and the balance compounds toward it.
How Much of the FIRE Number You Need, by Runway
The single biggest lever in Coast FIRE is time, because the discount factor is exponential. The table below shows the Coast number as a share of a full FIRE target at a 4% real return — roughly what the default 7% nominal and 3% inflation produce.
| Years to target age | Coast number as % of FIRE number | If your FIRE number is $1,000,000 |
|---|---|---|
| 5 | 82.2% | $821,900 |
| 10 | 67.6% | $675,600 |
| 15 | 55.5% | $555,300 |
| 20 | 45.6% | $456,400 |
| 25 | 37.5% | $375,100 |
| 30 | 30.8% | $308,300 |
| 35 | 25.3% | $253,400 |
| 40 | 20.8% | $208,300 |
Read down the column and the argument for saving early becomes arithmetic rather than exhortation: a 25-year-old aiming at 65 needs about a fifth of the eventual target, while a 55-year-old with the same goal needs more than four fifths of it. Each decade of delay roughly halves the work the market does for you. It also explains why Coast FIRE feels achievable to people who find full FIRE out of reach — the number you are chasing is a fraction of the headline one.
Coast FIRE Compared With the Other Variants
The FIRE family differs mainly in how much you spend and how much you keep earning. Coast FIRE is the one that changes your relationship with saving rather than with work.
| Variant | What it asks | What changes when you reach it |
|---|---|---|
| Coast FIRE | Is my portfolio big enough to grow into the target on its own? | You stop saving for retirement; you still work to cover today's bills. |
| Standard FIRE | Do I have 25× my annual spending? | Work becomes optional entirely. |
| Barista FIRE | Can part-time income plus a partial portfolio cover my spending? | You work fewer hours, often for benefits rather than salary. |
| Lean FIRE | Can I retire on a deliberately small budget? | Nothing about work; the target is lowered instead. |
| Fat FIRE | Can I retire without cutting my lifestyle at all? | Nothing about work; the target is raised instead. |
These are not exclusive. Most people who reach Coast FIRE keep contributing anyway, because the same maths that says they could stop also says that continuing pulls the retirement date forward. The value of knowing your Coast number is the freedom it buys in between: it is the point where a pay cut for a better job, a sabbatical, or a few years of part-time work stops threatening your retirement. Compare the paths side by side with the FIRE Calculator and the Barista FIRE Calculator, or work backwards from a fixed retirement date with the Reverse FIRE Calculator.
What This Model Leaves Out
The projection uses one constant return every year. Real markets do not: they deliver long flat stretches and sudden recoveries, and the order in which those arrive changes the outcome even when the average is identical. For a saver still accumulating, that sequence risk is survivable — you are buying through the drawdown. Treat the Coast number as the centre of a range, not a threshold you cross once and never revisit.
The model also ignores taxes entirely. Money in a tax-deferred account is worth less than the same balance in a Roth or an ISA, because a withdrawal will be taxed as income, and a taxable brokerage account carries embedded capital gains. Two people with identical balances can therefore have genuinely different Coast numbers. Investment fees are absent too — a 0.9% fund fee against a 0.05% index fund costs roughly 0.85 points of real return, which over 35 years is a very large difference in the discount factor.
Two behaviours of the page are worth knowing. The growth chart plots the nominal balance while the Coast and FIRE numbers are in today's dollars, so the curve meets the FIRE line earlier than your real-terms coast date — read the headline figure, not the crossing point, as the answer. And your inputs are written into the page URL and saved in your browser's local storage so the FIRE tools share a profile; nothing is transmitted, but clear the fields before sharing the link if you would rather not pass your balances on.
This calculator is an educational estimate, not financial advice. It assumes a constant annual return and models neither taxes nor fees. Before changing your savings rate or leaving a job, check the numbers against your own accounts and consider talking to a licensed financial planner.
Frequently Asked Questions
The tool divides your annual retirement expenses by your safe withdrawal rate to get a full FIRE number, then discounts that back to today using your real return over the years remaining before your target age: Coast Number = FIRE Number ÷ (1 + real return)^years. The real return is (1 + nominal) ÷ (1 + inflation) − 1, so 7% returns with 3% inflation give 3.88%, not 4%. Every figure on the page is therefore in today's dollars.
No — that is full FIRE. At Coast FIRE your retirement is funded by compounding alone, but you still need income for current living costs: rent, food, insurance, everything you spend on now. What changes is that none of that income has to go into retirement accounts, which is why people use it to justify a lower-paid but better job, fewer hours, or a career break.
It is an arithmetic result from your assumptions, not a forecast. A single constant return is a simplification of a market that moves in irregular stretches, and the model excludes taxes, investment fees and any change in your spending. Shifting the expected return by one point moves a 35-year Coast number by roughly a third, so treat the output as a range and re-run it as your circumstances change.
No. Every calculation runs in JavaScript in your browser and nothing is uploaded. Your inputs are stored two ways locally: in the page URL, so a result can be bookmarked or reloaded, and in your browser's local storage under a shared FIRE profile so the other calculators on this site pre-fill with the same figures. Clearing site data removes both.
4% is the common default and comes from the Trinity study of historical US 30-year retirements; it implies a portfolio of 25 times annual spending. Many people retiring early use 3.25% to 3.5% because a 40- or 50-year horizon gives sequence risk more time to do damage, which raises the multiple to roughly 29× or 31×. Test both here, and use the Withdrawal Rate Calculator to see how long a portfolio lasts at each.
Coast FIRE is about contributions: your retirement fund is already on track, so you stop adding to it but still earn enough to cover today's expenses. Barista FIRE is about income: you draw partly on the portfolio and partly on part-time work, often taken for health coverage rather than pay. Coast FIRE typically comes first and needs a smaller balance, since it relies on decades of untouched compounding.
Because the discount factor is exponential in both the return and the number of years. Dropping the expected return from 7% to 6% cuts the real return from 3.88% to 2.91%, which over 35 years raises a $1,000,000 target's Coast number from about $264,000 to about $366,000. Pushing the target age out by five years moves it the other way just as sharply. If two of your inputs are uncertain, change them one at a time to see which one your plan actually hinges on.
Most people do, and the maths supports it. Coasting is permission to stop, not an instruction — every further contribution either brings the retirement date forward or raises the standard of living it funds. The practical use of the number is knowing you have a floor, so a redundancy, a sabbatical or a move into lower-paid work no longer puts retirement at risk.
Use Cases
Deciding Whether to Take a Pay Cut
A developer offered a role at a non-profit for 30% less checks whether the existing balance already exceeds the Coast number. If it does, the salary only has to cover living costs, and the retirement contributions being lost stop being the deciding factor.
Costing a Career Break
Before a year of parental leave or study, set contributions to zero and confirm the portfolio still reaches the target by 65. The gap between your balance and the Coast number is the real price of the year off, expressed in dollars rather than anxiety.
Setting a First Milestone in Your Twenties
A 25-year-old facing a seven-figure FIRE number gets a target around a fifth of it instead. Raising the target age to 65 gives a 40-year runway and a goal that a decade of consistent saving can genuinely reach.
Stress-Testing an Optimistic Plan
Run the same inputs at 7%, 6% and 5% expected returns and note how far the Coast number moves. If the plan only works at the top figure, that is the finding — and a reason to keep contributing past the point where the model says you could stop.
Running an Annual Review With a Partner
Combine both portfolios and both retirement budgets once a year, then compare the balance against the Coast number. The percentage on the progress bar is a single figure two people can agree on without arguing about individual line items.
Choosing Between Extra Saving and Paying Down a Mortgage
If the balance is already past the Coast number, further retirement contributions are optional — which frees the surplus for overpayments that cut the retirement spending figure itself, and with it the FIRE number this tool starts from.