Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Result
Coast FIRE number
$246,382
Still needed to coast
$66,382
Progress to Coast FIRE
73.1%
Full FIRE number
$1,500,000
Projected balance at retirement
$1,095,858
Surplus or shortfall vs target
-$404,142
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How to use this
- 1Enter current invested balance ($).
- 2Enter current age.
- 3Enter retirement age.
- 4Enter annual spending in retirement (today's dollars) ($).
- 5Enter safe withdrawal rate (%).
- 6Enter real return after inflation (%).
- 7Read your coast fire number on the right — it updates as you type.
- 8Hit Share to keep the scenario or send it to someone.
About this calculator
Coast FIRE is the point where compounding alone gets you to your number. Hitting it does not mean quitting — it means you only need to cover current expenses from here.
Worked example
Using the values the calculator loads with:
Inputs
- Current invested balance: 180000 $
- Current age: 34
- Retirement age: 65
- Annual spending in retirement (today's dollars): 60000 $
- Safe withdrawal rate: 4 %
- Real return after inflation: 6 %
Results
- Coast FIRE number: $246,382.26
- Still needed to coast: $66,382.26
- Progress to Coast FIRE: 73.1%
- Full FIRE number: $1,500,000.00
- Projected balance at retirement: $1,095,858.12
- Surplus or shortfall vs target: -$404,141.88
What each field means
Inputs
- Current invested balance ($)
- The current invested balance used in the calculation, measured in $. Starts at 180000 $ so you have a working example on load.
- Current age
- The current age used in the calculation. Starts at 34 so you have a working example on load. Accepted range: 15–80.
- Retirement age
- The retirement age used in the calculation. Starts at 65 so you have a working example on load. Accepted range: 30–90.
- Annual spending in retirement (today's dollars) ($)
- The annual spending in retirement (today's dollars) used in the calculation, measured in $. Starts at 60000 $ so you have a working example on load.
- Safe withdrawal rate (%)
- The safe withdrawal rate used in the calculation, measured in %. Starts at 4 % so you have a working example on load. Accepted range: 2–8 %.
- Real return after inflation (%)
- The real return after inflation used in the calculation, measured in %. Starts at 6 % so you have a working example on load. Accepted range: 0–12 %.
Results
- Coast FIRE number
- Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Still needed to coast
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Progress to Coast FIRE
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Full FIRE number
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Projected balance at retirement
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Surplus or shortfall vs target
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the coast fire calculator work?
Coast FIRE is the point where compounding alone gets you to your number. Hitting it does not mean quitting — it means you only need to cover current expenses from here. The underlying maths is: Coast number = Target ÷ (1 + real return)^(years to retirement).
What do I need to enter?
6 values: current invested balance, current age, retirement age, annual spending in retirement (today's dollars), safe withdrawal rate, and real return after inflation. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the coast fire number result mean?
It is returned as a money amount in US dollars and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
Who is this tool for?
It's built for anyone comparing money scenarios before committing — budgeting a payment, sanity-checking a quote, or seeing what a change in rate or term actually costs.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Coast FIRE Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/coast-fire
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/coast-fire" target="_blank" rel="noopener">Coast FIRE Calculator — RevenueLab</a> (2026).</p>
Source: [Coast FIRE Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/coast-fire) (2026).