I don’t believe there’s a consensus or standard definition of exactly what constitutes fatFIRE, so I get to go ahead and make my own.
The average American household spends somewhere between $50,000 and $60,000 in 2018. A leanFIRE budget is at most half of that. I’d say fatFIRE is somewhere in the neighborhood of double. Since we like round, even numbers, let’s call a fatFIRE budget $100,000 a year.