What is Coast FIRE?
Coast FIRE, also called Coast FI, is the point where your existing long-term investments are mathematically large enough to grow to your retirement target by your chosen retirement age without any additional retirement contributions.
Reaching Coast FIRE does not mean you have enough money to stop working today. It means that, under the return, inflation and withdrawal assumptions you chose, future compound growth is expected to finish funding the retirement target while your current income only needs to cover your life before retirement.
The Coast FIRE formula
The calculation starts with a full retirement target:
Retirement target = annual retirement spending ÷ withdrawal rateThen it discounts that future target back over the years remaining until retirement:
Coast FIRE number = retirement target ÷ (1 + real return)years to retirementThis is present-value math. Instead of asking how much today's money will become, Coast FIRE asks how much must be invested today to grow into a specified future retirement portfolio.
Why this calculator uses real returns
If retirement spending is entered in today's purchasing power, the investment growth assumption should also be expressed in real purchasing-power terms. Otherwise nominal future dollars and today's dollars are mixed in the same calculation.
This calculator uses a compounded inflation adjustment:
Real return = (1 + nominal return − fee rate) ÷ (1 + inflation rate) − 1For example, a 7% nominal return and 3% inflation are not exactly a 4% real return. Ignoring fees, the compounded relationship gives approximately 3.88%.
Investment fees matter
Fees reduce the return that remains available to compound. Because Coast FIRE can involve decades of growth, even a small annual difference can materially change the balance required today.
The calculator therefore includes an optional annual fee assumption instead of silently assuming that the full market return reaches your portfolio.
How the retirement target is calculated
If you expect 50,000 of annual retirement spending and use a 4% withdrawal rate:
50,000 ÷ 0.04 = 1,250,000That 1.25 million is the full retirement target in today's purchasing power. A 4% rate is equivalent to 25 times annual spending. A 3.5% rate requires about 28.57 times spending, while a 5% rate requires 20 times spending.
The 4% rule is an assumption, not a promise
The familiar 4% withdrawal convention is rooted in historical retirement research, including work by Cooley, Hubbard and Walz. Their studies examined historical stock-and-bond portfolios across different withdrawal rates and retirement horizons.
Historical success does not turn 4% into a guaranteed future withdrawal rate. Portfolio allocation, retirement length, market valuations, taxes, fees, spending flexibility and future returns all matter. This calculator leaves the withdrawal rate editable for that reason.
Worked Coast FIRE example
Imagine someone age 35 who wants 60,000 of annual retirement spending at age 65. At a 4% withdrawal assumption, the full target is:
60,000 ÷ 0.04 = 1,500,000If nominal return is 7%, inflation is 3%, and fees are zero, real return is about 3.88%. There are 30 years until age 65:
Coast FIRE ≈ 1,500,000 ÷ 1.038830 ≈ 478,000If the person already has roughly that amount invested, the model says no additional contributions are required to reach the 1.5 million target in today's purchasing power by 65.
What counts as your current invested portfolio?
Use assets that are genuinely intended to fund the retirement goal and are expected to remain invested. Depending on your circumstances, that might include retirement accounts and long-term taxable investments.
Do not automatically count emergency cash, money earmarked for a home purchase, business working capital, or assets you expect to spend before retirement. The Coast FIRE calculation assumes the entered portfolio remains available to compound toward retirement.
Current portfolio versus Coast FIRE number
If your current invested balance is below the Coast FIRE number, the difference is your current gap:
Gap = Coast FIRE number − current invested portfolioIf the result is negative, you have a mathematical surplus relative to the Coast target under the entered assumptions.
What does “already Coast FIRE” mean?
It means your current portfolio is at least as large as the present-value Coast target. It does not mean future returns are guaranteed, that you can spend the portfolio now, or that you never need to revisit the plan.
Estimating your Coast FIRE age
If you have not reached Coast FIRE today and enter a monthly contribution, this calculator projects your balance forward using the same real-return assumption. At each future age, it compares that projected balance with the Coast target for that age.
The first age at which the projected balance meets or exceeds the target is the estimated Coast FIRE age. Because the model assumes smooth returns, treat the result as a scenario rather than a precise date.
Why the Coast number rises as you get older
At a fixed retirement age, a younger investor has more years for compound growth to do the work. As retirement approaches, fewer compounding years remain, so the balance required to coast becomes larger.
At the retirement age itself, the Coast FIRE number and full retirement target are the same because there is no remaining growth period.
How monthly contributions affect Coast FIRE
Your current Coast FIRE number is determined by retirement target, real return and years remaining. A contribution does not change that mathematical target today.
Instead, contributions change how quickly your portfolio may catch the moving Coast target. That is why this calculator treats monthly contributions as an optional path-to-Coast input rather than part of the Coast-number formula itself.
Coasting now versus continuing to contribute
The results show two separate projections. “Coast now” assumes zero future contributions and compounds only your current invested balance. The contribution projection assumes you keep adding the entered monthly amount through retirement.
Comparing them makes the opportunity cost of stopping contributions visible without claiming that either path is the right decision.
Why assumptions matter so much
Coast FIRE is unusually sensitive to long-term return assumptions because compounding is raised to the number of years remaining. A one-percentage-point difference repeated for 20, 30 or 40 years can substantially change today's required balance.
Withdrawal rate is also powerful because it directly changes the full retirement target. Inflation matters because it reduces purchasing-power growth.
Stress-test your Coast FIRE plan
Do not rely on a single optimistic scenario. Recalculate with:
- a lower nominal investment return;
- higher inflation;
- higher investment fees;
- a lower withdrawal rate;
- higher retirement spending;
- an earlier target retirement age.
If the conclusion changes dramatically under modest adjustments, the plan has little margin for error.
Sequence-of-returns risk
The calculator uses a constant annual real return for clarity. Real markets do not grow smoothly. A portfolio can experience losses, strong gains and long flat periods.
Before retirement, the order of returns can affect the path to the Coast target, especially when contributions are still being made. During retirement, sequence risk becomes even more important because withdrawals interact with market losses.
Why average return is not guaranteed return
A long-term average does not mean the portfolio earns that percentage every year. Two portfolios can have similar average returns but very different paths and outcomes.
Government investor education resources emphasize that compound growth can be modeled with an estimated interest rate, but an estimate remains an assumption. Past performance cannot promise future results.
Inflation and today's dollars
Expressing the model in today's dollars makes retirement spending easier to interpret. If you say you want 50,000 per year in retirement, the calculator treats that as 50,000 of today's purchasing power rather than the nominal number printed on future currency.
The real-return adjustment is what keeps the target and projected balances on the same purchasing-power basis.
Taxes are not modeled
Tax treatment depends on country, account type, contribution rules, withdrawals, income and future law. A universal calculator cannot responsibly assume one tax system.
If taxes will materially reduce the money available for retirement spending or investment growth, account for that in your own spending, return or portfolio planning with appropriate professional guidance.
Social Security, pensions and other retirement income
If you expect reliable retirement income from a pension, public retirement program, annuity or another source, you may choose to estimate only the spending that must be supported by the investment portfolio.
Do not subtract uncertain income as though it were guaranteed. Eligibility rules, taxation, inflation adjustments and benefit formulas vary by system and jurisdiction.
Coast FIRE versus traditional FIRE
| Concept | Main question | Can you stop working immediately? |
|---|---|---|
| Coast FIRE | Can current investments grow to the retirement target without more contributions? | Not necessarily |
| Traditional FIRE | Is the portfolio already large enough to support current retirement withdrawals? | Potentially, under the plan's assumptions |
Coast FIRE is therefore usually an earlier milestone than full financial independence.
Coast FIRE versus Barista FIRE
Coast FIRE focuses on stopping retirement contributions while still earning enough to cover current living expenses. Barista FIRE generally describes a situation where investments cover part of current expenses and part-time or lower-intensity work covers the rest.
The concepts can overlap in real life, but the mathematics and cash-flow questions are different.
Coast FIRE does not require quitting your career
Some people use Coast FIRE only as a resilience milestone. Reaching it may provide flexibility to save less, change careers, work fewer hours, prioritize family, or simply continue investing and build a larger margin.
The calculator should not tell you what lifestyle decision to make. Its job is to make the financial assumption visible.
Retirement spending is often the hardest input
A Coast FIRE result can look precise while being driven by an uncertain spending estimate. Consider housing, food, transportation, healthcare, insurance, taxes, travel, hobbies and support for dependents.
Some expenses may disappear before retirement while others may increase. Use today's realistic spending as a starting point and update it periodically.
Healthcare and long retirements
Healthcare costs, long-term care needs and unusually long retirement horizons can make a simple withdrawal-rate target less reliable. A person retiring very early may need the portfolio to support withdrawals for much longer than the 30-year horizons commonly discussed in classic withdrawal research.
That is another reason to keep the withdrawal rate editable and stress-test the plan.
Why fees deserve their own input
Many simple Coast FIRE calculators subtract inflation from return but omit investment costs. Over a long horizon, ongoing fund expenses, advisory charges or platform costs can reduce compound growth.
This calculator subtracts the entered annual fee rate from nominal return before converting to a real return. It is still a simplified annual model, but the assumption is transparent.
Can the real return be negative?
Yes. If inflation and fees exceed nominal investment return, purchasing power shrinks. The formula can still be evaluated as long as the resulting growth factor remains positive.
In a negative-real-return scenario, a future retirement target requires more purchasing-power capital today rather than less.
Common Coast FIRE mistakes
- Using nominal returns with spending stated in today's dollars.
- Assuming 4% is universally safe. Withdrawal-rate research depends on horizon and portfolio assumptions.
- Counting emergency savings as permanent retirement investments.
- Ignoring fees.
- Using an unrealistically low retirement-spending estimate.
- Treating average returns as guaranteed annual returns.
- Assuming reaching Coast FIRE means you can retire immediately.
- Ignoring taxes, pensions or other important personal cash flows.
- Never updating the calculation as age, spending and portfolio value change.
How to verify a Coast FIRE calculation
First calculate the full retirement target by dividing annual spending by the withdrawal rate. Then calculate years to retirement. Convert the nominal return to a real return using inflation and any modeled fees. Finally discount the retirement target back by that real return.
As a cross-check, compound the calculated Coast FIRE number forward for the same number of years. It should return to the full retirement target, apart from rounding.
Frequently asked questions
What is my Coast FIRE number?
It is the amount that would need to be invested today so that, under your assumed real return and with no further contributions, it grows to your retirement target by your target age.
Does Coast FIRE mean I can retire now?
No. It usually means future retirement contributions may no longer be mathematically required under the assumptions; you still need to fund your current living costs.
Why does the calculator ask for inflation?
Inflation converts nominal investment growth into real purchasing-power growth so today's spending can be compared consistently with future balances.
Is 4% the only withdrawal rate I can use?
No. The field is editable because an appropriate withdrawal assumption depends on the plan, retirement horizon, portfolio and risk tolerance.
Do monthly contributions change today's Coast FIRE number?
No. They affect how quickly your portfolio may reach the Coast target, not the present-value target itself.
Should I include my home in current investments?
Only if your retirement plan genuinely expects that value to fund the portfolio target. A home you intend to keep living in is not automatically an investable retirement balance.
Are taxes included?
No. Tax systems and account rules vary widely, so the calculator does not invent a universal tax assumption.
What if I have already reached Coast FIRE?
The calculator shows a surplus and projects what your current portfolio could become if no additional contributions are made. Whether you actually reduce saving is a separate planning decision.
How often should I recalculate?
Revisit the estimate when your portfolio, retirement age, spending target or long-term assumptions materially change.
Is Coast FIRE guaranteed?
No. It is deterministic compound-growth math based on assumptions. Actual markets, inflation, fees and life circumstances can differ substantially.
Final note: Coast FIRE is most useful as a transparent milestone, not a finish-line promise. Use realistic retirement spending, keep nominal returns and inflation consistent, include fees you expect to pay, and test less favorable scenarios. If your current portfolio remains above the Coast target across several reasonable assumptions, the result is more informative than a single optimistic calculation.