FIRE: The Math Behind Early Retirement

This used to be a back-of-the-envelope job. Now it is one tap, but the logic has not changed. Financial Independence, Retire Early sounds like a lifestyle trend. It's actually a math problem with one clean answer: 25× your annual spending.

The 4% rule

Withdraw 4% of your portfolio in year one, adjust for inflation each year. Historically lasts 30+ years.

25× = financial independence

$40,000/year spending → need $1,000,000. $80,000 → $2,000,000.

Lean vs fat FIRE

Lean: small portfolio + frugal lifestyle. Fat: large portfolio + normal lifestyle. Coast: enough that compounding alone funds traditional retirement.

The savings rate that gets you there

50% savings rate → retire in ~17 years. 70% → ~9 years. Income matters; savings rate matters more.

Pro tips

• Lower your spending baseline before you grow your investments — it cuts the target and accelerates the savings rate.
• Always stress-test with sequence-of-returns risk; first-five-year crashes are the killers.

Frequently asked questions

Is the 4% rule still valid? Originally backtested on 30-year retirements. For 50+ year retirements, drop to 3.25–3.5% to be safe.

What about healthcare? Biggest variable, especially in the US. Plan separately, often outside the 4% draw.

Whatever number you land on, sanity-check it against a second method or a quick estimate in your head.