About
Fat FIRE: maintain or upgrade lifestyle in early retirement. Annual spending $100K+. $2.5M minimum, $5M+ common. Travel, premium healthcare, dining all included. Often paired with lower withdrawal rate (3-3.5%) for safety.
Fat FIRE differs from Lean and regular FIRE on both the spending input and the safety margin. Bengen's 1994 paper, refined by the Trinity Study, established the 4% safe-withdrawal rule for 30-year horizons on a 50-75% US-equity portfolio. Fat FIRE plans usually run 50+ year horizons (retiring in your 40s) and weather sequence-of-returns risk by dropping the withdrawal rate to 3% or 3.5%. At 3%, your number is 33.3x annual spending, not 25x. So a $150,000 lifestyle plus $25,000 of pre-Medicare ACA healthcare and $20,000 of federal and state tax overhead becomes $195,000 of gross annual draw, which at 3% needs $6.5M, not the $4.875M a naive 4% multiple would give. The calculator above keeps SWR adjustable so you can compare both anchors and see how sensitive Fat FIRE is to the rate you trust.
Formula
Frequently asked questions
How accurate is the Fat 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 Fat 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 Fat 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 Fat 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 Fat 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 Fat 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 fat 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 Fat FIRE Calculator accurate?
The Fat FIRE Calculator applies the standard formula for fat 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 Fat 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.
How much should I add for pre-Medicare healthcare?
If you retire before age 65 in the US and lose employer coverage, ACA marketplace premiums plus deductibles for a family of four routinely land at $20,000 to $30,000 a year before subsidies, with $9,200 (individual) or $18,400 (family) out-of-pocket maximums in 2026. Subsidies phase out as MAGI rises, so high-spend Fat FIRE plans usually budget the full unsubsidized cost. Budget separately for dental, vision, and long-term-care, none of which Medicare covers.
Why use a 3% withdrawal rate instead of 4%?
The 4% rule was solved for 30-year horizons. Wade Pfau's and ERN's safe-withdrawal research show that for 50- and 60-year horizons, the 95th-percentile safe rate drops to about 3.0-3.25%. Fat FIRE retirees in their 40s face that longer horizon and richer baseline spending they would not want to cut in a downturn, so a 3% to 3.5% rate buys ~25% more headroom against a bad-sequence first decade.
How to use the Fat FIRE Calculator
The Fat 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 Fat 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.