What Is FIRE? Financial Independence, Retire Early Explained

FIRE = Financial Independence, Retire Early. The idea: save aggressively (50–70% of income), invest it, and retire decades earlier than traditional retirement age.

The 4% Rule

If you've saved 25× your annual expenses, you can withdraw 4%/year forever (statistically). Annual expenses $40K → need $1M invested. That's your 'FIRE number.'

FIRE Variants

LeanFIRE ($25–40K/yr expenses, $750K–$1M number), FatFIRE ($100K+/yr, $2.5M+), CoastFIRE (saved enough that compound interest gets you to traditional retirement), BaristaFIRE (part-time work + savings).

The arithmetic in one line

Annual spending × 25 = the portfolio you need. Spend $40,000 a year and the target is $1,000,000. Spend $60,000 and it is $1,500,000. The multiplier is the inverse of a 4% withdrawal rate, which came out of the Trinity Study's finding that a 50/50 to 75/25 stock-and-bond portfolio historically survived thirty years of inflation-adjusted 4% withdrawals in the overwhelming majority of historical periods. Note what the sum depends on: spending, not income. Two people earning the same amount have completely different FIRE numbers.

Why the savings rate matters more than the salary

The years to financial independence depend almost entirely on the percentage of income you save, because saving more simultaneously builds the portfolio faster and shrinks the target it has to reach. Someone saving 10% of their income is looking at a working life measured in decades; someone saving 50% is looking at something closer to a decade and a half; someone saving 70% is looking at under a decade. A raise that all goes to spending moves the date not at all — it raises the target by 25× the new spending while adding nothing to the savings rate.

• FIRE number calculator
• Savings rate calculator
• Compound interest calculator

The four flavours people mean

Lean FIRE is the same maths on a deliberately small budget — a smaller number reached sooner, with less margin if anything goes wrong. Fat FIRE is the same maths on a comfortable budget, which takes materially longer. Barista FIRE means saving enough that a part-time job covers the gap, usually chosen for the health cover as much as the income. Coast FIRE is the one most people can actually reach: enough invested early that compounding alone gets you to the full number by retirement age, so you never have to save another dollar, only cover current spending.

What the 4% rule does not cover

It was derived from thirty-year retirements, and a retirement starting at 40 may run fifty. It assumes you hold through crashes rather than selling into them, which is a behavioural assumption, not a financial one. It says nothing about US health insurance before Medicare age, which is the single largest unbudgeted cost in early retirement. And sequence-of-returns risk is real: a bad first five years does far more damage than the same returns arriving later. Most people who have done it treat 4% as a planning anchor and then build flexibility — variable spending, a cash buffer, some earned income — around it.

Related reading: FIRE Movement Explained.