Your FIRE number depends entirely on how much you plan to spend. See how a minimalist budget and a comfortable budget change your target and your retirement age, side by side.
Both are financial independence, but built around very different lifestyles. Lean FIRE targets a minimalist budget — often at or below typical living costs — which lowers your FIRE number and gets you there faster, but leaves less room for error or lifestyle changes. Fat FIRE targets a comfortable, even generous budget, which takes longer to reach but gives far more flexibility once you're there.
Because your FIRE number is spending × 25 (at a 4% withdrawal rate), every extra $10,000 of annual spending adds $250,000 to your target. Small lifestyle differences compound into very different timelines.
Many people aim for something in between — a number that covers their real expected spending, not an extreme in either direction. If you want a single target based on your actual planned spending rather than a lean/fat comparison, try the FIRE Number calculator.