What's the difference between Lean FIRE and Fat FIRE?

Lean FIRE and Fat FIRE describe the spending level you're retiring into. Lean FIRE means living frugally, often on roughly $25,000–$40,000 a year, which keeps your target portfolio small — maybe $625,000 to $1 million at 25x. Fat FIRE means retiring without budget compromises, typically $100,000+ a year, requiring $2.5 million or more. Regular FIRE sits in between. The right one depends on your real values, family size, and where you live, not on what looks impressive online. Lean FIRE reaches the finish line years sooner but leaves little cushion for surprises like a medical bill or a bad market, so many people pair it with the ability to earn again. Fat FIRE costs more years of work but is far more resilient. Pin down your number first, then decide which camp fits.