About
Coast FIRE: save enough today that compound growth alone funds retirement, no new contributions needed. Frees you to pursue lower-paying meaningful work, take time off, or downshift career. Typically 25-35% of full FIRE number.
The math sits on top of two anchors most FIRE plans share. First, the Trinity Study (Cooley, Hubbard and Walz, 1998) found a 4% inflation-adjusted withdrawal rate survived 30-year retirements in the majority of historical stock and bond windows. That gives the standard 25x annual spending FIRE target. Second, Mr Money Mustache's 2012 savings-rate-to-years table compresses the same math into a simple curve: a 50% savings rate retires in about 17 working years, 65% in about 10.5, and 75% in about 7. Coast FIRE inverts that table by asking what balance today will, with no further contributions, grow into the 25x target by your chosen retirement age. A 7% real return is the long-run US equity baseline that backs the 4% rule. Drop the return to 5% and your Coast number rises sharply, because the discount factor (1+r)^years gets weaker the further out compounding has to reach.
Formula
Frequently asked questions
How accurate is the Coast FIRE Calculator?
It applies the standard formula. Accuracy is limited only by your input precision. For decisions with material consequences (taxes, medical, legal, structural), use the result as a starting point and verify with a qualified professional in the relevant field.
Is the Coast FIRE Calculator free to use?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads around the tool but not inside the calculation flow.
Are my inputs saved anywhere?
No. All inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but the analytics never see what you type into the form.
Can I use the Coast FIRE Calculator on my phone?
Yes. The tool is responsive and tested on iOS Safari, Android Chrome, and major desktop browsers. Touch targets meet Apple's 44pt and Google's 48dp minimum.
Does the Coast FIRE Calculator work offline?
Yes. Once the page has loaded, it works without internet. The calculation runs in JavaScript on your device.
How do I report a bug or suggest improvement to the Coast FIRE Calculator?
Email hi@3tej.com with the URL of this page and a description of what you saw vs expected. We typically respond within 72 hours.
Can I share results from the Coast FIRE Calculator?
Take a screenshot or copy the output. The page doesn't generate shareable URLs for specific calculations - inputs stay in your browser only.
Why are the results different from another coast fire tool?
Most likely: different formula assumptions, different default values, different rounding rules, or different applicable rates. Check the methodology if both tools document it. Both can be valid for different scenarios.
Is the Coast FIRE Calculator accurate?
The Coast FIRE Calculator applies the standard formula for coast fire. Accuracy is limited only by your input precision. For decisions with material consequences, use the result as a starting point and verify with a qualified professional or the relevant official source.
Is the Coast FIRE Calculator free?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads that appear around the tool but not inside the calculation flow.
Are my inputs saved?
No. Inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but does not see what you type into the form.
Coast FIRE vs Lean FIRE vs Fat FIRE: which target should I aim for?
They are different goals, not different formulas. Lean FIRE targets a 25x multiple of a bare-bones annual budget (often $25k-$40k). Fat FIRE targets 25x of a high-spend lifestyle ($100k+ annual). Coast FIRE is a milestone on the way to any of the three: the balance today that, untouched, grows into your chosen 25x by retirement. Many planners hit Coast Lean first, keep working part-time, and ride compounding toward Coast regular or Coast Fat.
How to use the Coast FIRE Calculator
The Coast FIRE Calculator is a browser-based tool that runs entirely on your device. Inputs you enter never reach a server - all calculations happen client-side in JavaScript. This means:
- Privacy: nothing is logged, sent, or stored by 3Tej. Inputs disappear when you close the tab.
- Speed: results update as you type. No network round trip.
- Offline use: once the page is cached, it works without internet.
- No signup: no account, no email, no rate limits.
Step by step
- Enter your inputs in the form above. Each field is labeled with its unit (currency, percent, kg, etc.) and the expected range.
- Read the result as it updates. The number reflects the formula commonly accepted in Coast FIRE-related calculations.
- Adjust to see sensitivity: change one input at a time and watch how the output moves. This is the fastest way to understand which variable matters most.
- Copy or screenshot the result for later reference. The page state persists for the session if your browser allows it.
When you would use this
- Quick estimates: when you need a number now and don't want to open a spreadsheet.
- Sensitivity analysis: testing how a result changes as inputs vary, before committing to a real-world decision.
- Comparison: running the same calculation with different inputs to compare options side by side.
- Learning: building intuition for how the underlying math behaves.
- Documentation: capturing a snapshot of inputs and outputs at a point in time.