How to Calculate Lean FIRE
What is Lean FIRE?
Lean FIRE is a form of financial independence achieved on a very frugal budget, typically below $40,000/year. It requires a smaller portfolio but demands strict spending discipline.
Formula
annual_spending = (annual_expenses / withdrawal_rate); FV_needed = annual_spending × 25 (4% rule)
- expenses
- Annual expenses ($) — Annual spending target
- wr
- Withdrawal rate (%) — Safe rate to withdraw yearly (typically 3–4%)
- portfolio
- Portfolio needed ($) — Total amount needed for retirement
Step-by-Step Guide
- 1FIRE Number = Annual Expenses × 25 (4% safe withdrawal rate)
- 2Lean FIRE targets expenses 20–40% below average
- 3Typical Lean FIRE budget: $25,000–$40,000/year
- 4Geographic arbitrage (lower cost of living) is common
Worked Examples
Input
$25,000/year lean expenses
Result
FIRE number $625,000
Input
$30,000/year
Result
FIRE number $750,000
Input
$20,000/year (very lean)
Result
FIRE number $500,000
Frequently Asked Questions
What is Lean FIRE?
Retiring early on low expenses (e.g., $25K–40K/year). Less savings needed than Fat FIRE.
Is the 4% rule safe?
The 4% rule (withdraw 4% annually, adjusted for inflation) has about 95% success over 30 years. More conservative: 3–3.5%.
How do I know my annual expenses?
Track spending for 6–12 months, include taxes, healthcare, insurance. Round up slightly for safety.
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