Coast FIRE vs Lean FIRE vs Fat FIRE: What's the Difference?

Not every FIRE journey looks the same. Once you understand the basic 4%-rule math, it helps to know the common variants people use to describe their specific situation.

Lean FIRE describes reaching financial independence with a relatively modest annual budget. It requires a smaller FIRE number but demands sustained frugality, both before and after retiring.

Fat FIRE is the opposite end of the spectrum: financial independence at a higher, more comfortable spending level. It requires a much larger portfolio but offers more flexibility and cushion.

Coast FIRE describes a middle milestone rather than a full retirement: the point at which your current invested portfolio, left alone with no further contributions, is projected to grow into your full FIRE number by your target retirement age through compound returns alone.

These labels are informal community terms, not strict financial definitions. What matters most is using the underlying math — your expenses, expected return, and withdrawal rate — to define your own version of FIRE.