About this tool
The FIRE (Financial Independence, Retire Early) number is the portfolio size at which your investments can sustain you indefinitely. The original Trinity Study (1998) showed that withdrawing 4 percent annually has historically supported 30-year retirements with high success. Multiply your annual expenses by 25 (the inverse of 4 percent) to get your target.
How it works
FIRE = (annual_expenses × buffer) / SWR - Trinity Study supports 4% withdrawal for 30+ year retirement
Enter your monthly expenses. The calculator multiplies by 12 for annual, optionally adds a 15 percent inflation buffer, and divides by your chosen safe withdrawal rate. The result is the portfolio you need.
How to use the FIRE Number Calculator
The FIRE Number 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 FIRE Number-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.
Frequently asked questions
Why 25×?
Because 1 / 0.04 = 25. If you withdraw 4% per year and your portfolio earns more than 4% on average (after inflation), you never run out.
Is the 4% rule still valid in 2026?
Studies of post-2000 markets suggest 3.5% is more conservative for 40+ year retirements. Use 3% if you plan to retire in your 30s or 40s.
Lean FIRE vs Fat FIRE?
Lean = bare-minimum frugal lifestyle (often 50% of typical). Fat = 2× to support family, travel, and healthcare uncertainty.
What about healthcare in early retirement?
In the US, ACA subsidies depend on income. Many FIRE planners budget $1,000 to $1,500 per month for a couple under 65 in their plan.
Is the FIRE Number Calculator accurate?
The FIRE Number Calculator applies the standard formula for fire number. 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 FIRE Number 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.
Can I use the FIRE Number 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 guidance.
How do I report a bug or suggest improvement to the FIRE Number 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 and update calculators when rules or formulas change.
How accurate is the FIRE Number 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 FIRE Number 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.
Does the FIRE Number Calculator work offline?
Yes. Once the page has loaded, it works without internet. The calculation runs in JavaScript on your device.
Can I share results from the FIRE Number 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 fire number 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.
