A free, open-source FIRE (Financial Independence, Retire Early) calculator that runs in a single HTML file with zero dependencies.

Calculates your numbers for Coast FIRE, Barista FIRE, Fat FIRE, and Lean FIRE — instantly in your browser.

The math:
- FIRE Number = Annual Spending / 4% (Trinity Study safe withdrawal rate)
- Coast FIRE Number = FIRE Number / (1 + Real Return Rate)^Years

Default assumptions (all adjustable):
- Investment return: 10% (S&P 500 historical average)
- Inflation: 3%
- Safe withdrawal rate: 4%
- Real return: ~7%

No signup. No tracking. No server. Download the HTML file and run it offline.

Also available as a full web app at coastfirehub.com with interactive charts, Coast FIRE Grid, and a Chrome extension.

Features

  • Coast FIRE calculator — calculates how much to invest today
  • Barista FIRE calculator — part-time income + investments
  • Fat FIRE / Lean FIRE — different lifestyle spending levels
  • Coast FIRE Grid — lookup table by age
  • Real-time results — updates as you type
  • Zero dependencies — single HTML file, runs offline
  • Open source — MIT license
  • No account required — runs in browser, no data collection

Project Samples

fire-calculator Screenshot 1 fire-calculator Screenshot 2

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Registered

2026-04-12
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