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FIRE stands for Financial Independence, Retire Early. It’s both an idea and a community — a way to think about money that treats your portfolio as a source of income so work becomes optional, not required.
When your investments generate enough income to cover your annual expenses, you’ve reached financial independence. Whether you keep working, slow down, or fully retire is up to you — the math has bought you the choice.
“Enough” is the load-bearing word. A widely-cited rule of thumb — the 4% rule — says that a diversified portfolio can sustainably produce income equal to about 4% of its value each year. That means a portfolio 25 times your annual expenses is roughly the size you need. Research and real-world conditions move that number around (valuations, inflation, sequence of returns), but the logic is the same: your portfolio’s durable income has to cover how you live.
1 · Your FIRE number
The portfolio size that makes your current expenses sustainable — roughly 25× your annual spending at a 4% withdrawal rate.
How it’s calculated →2 · Your savings rate
What fraction of your take-home pay gets invested each year. Savings rate — not income — is what drives how fast FI arrives.
Why it matters most →3 · Years to FI
The output. Given your current portfolio, savings rate, and a reasonable return assumption, how long until the math works? Shorter is a lever, not a race.
Stress-test the result →The FIRE community uses “Lean FIRE” and “Fat FIRE” as shorthand for retiring on a smaller or more generous spending level. They’re popular terms, but they hide something important: what counts as “lean” or “fat” depends entirely on who you are and where you live. $40K/yr is spartan in San Francisco and comfortable in rural Mississippi. $150K/yr is affluent by US medians and modest by the lifestyle of a dual-income professional in Manhattan.
This calculator refuses to pigeon-hole you into those buckets. You set your retirement expenses directly; the math meets you at whatever number feels right for your life. If the community vocabulary helps you talk about it, the Lean FIRE and Fat FIRE articles are here as reference — but nothing in the app will tell you your plan is “Lean” or “Fat.”
Unlike Lean/Fat (spending-level labels), Coast and Barista FIRE are structural choices about how you get to FI. They change the sequence and composition of your plan, not just the dollar target. The calculator models both.
A sensible reading order if you’re new to all this:
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