Lean FIRE 25x Target Calculator 2027

Calculate Lean FIRE number using 25x rule — minimum portfolio for sustainable 4% withdrawal at $25-45k/year lean lifestyle. Compare with Fat FIRE for 2027.

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Trinity Study Origin

Three Trinity University finance professors (1998) studied 1926-1995 returns. Found 4% initial withdrawal (inflation-adjusted) lasted 30+ years in 95%+ of historical periods. Hence the '25x rule' (1/4% = 25).

Lean vs Regular vs Fat FIRE

Lean: $25-45k/year (rural, no kids, minimal travel). Regular: $50-75k/year (suburb, one child, modest travel). Fat: $100-200k/year (city, kids in private school, frequent travel).

4% Rule Limitations

Trinity Study used 30-year horizon. For 50+ year retirement (FIRE early), safer to use 3.25-3.5%. Sequence-of-returns risk highest first 10 years. Build 2-3 year cash buffer to ride bear markets.

Geographic Arbitrage

Lean FIRE in low-cost-of-living areas. $35k/yr lives well in rural Tennessee, Portugal, Mexico, Thailand. Same income = poverty in San Francisco, NYC, London. Choose location strategically.

Source: Trinity Study 1998, updated 2026 ERN safe-withdrawal-rate research. Last updated: May 2026.