What is a FIRE number?
FIRE — Financial Independence, Retire Early — is the point where your invested assets are large enough that a safe annual withdrawal covers your living costs forever. The core formula is beautifully simple: FIRE number = annual expenses ÷ safe withdrawal rate. At the common 4% rate that's 25 times your annual spending. Spend $40,000 a year and you need about $1,000,000.
Where the 4% comes from
The 4% rule descends from the Trinity study, which found that withdrawing 4% of a starting portfolio (adjusted for inflation) survived 30 years in almost all historical periods. Early retirees planning for 40–50 year horizons often use a more conservative 3–3.5%, which raises the target to 28–33x expenses. Lower the withdrawal rate in the calculator and watch the FIRE number climb — that's the price of extra safety over a longer retirement.
Two levers, both powerful
- Spending is the master variable. Because the target is a multiple of expenses, cutting $5,000 of annual spending lowers your FIRE number by $125,000 (at 4%) — and simultaneously frees cash to invest. Frugality works on both sides of the equation.
- Savings rate sets the timeline. The single biggest determinant of how soon you reach FIRE is the percentage of income you save. A 50% savings rate gets most people there in around 17 years regardless of income level.
Beyond the number
Reaching your FIRE number gives you options, not obligations — many "retire" into work they actually enjoy. Pair this with our withdrawal calculator to stress-test how long the money lasts, and mind sequence-of-returns risk in the early years. FIRE is less about never working again and more about never having to.