FIRE Calculator

FIRE stands for Financial Independence, Retire Early. Your FIRE number is the portfolio size at which investment returns alone can sustainably cover your living expenses, so paid work becomes optional. It's calculated as your annual expenses divided by a withdrawal rate — at the classic 4% rate, that's annual expenses x 25.

The 4% rule traces to William Bengen's 1994 research and the 1998 Trinity Study (Cooley, Hubbard, and Walz), which backtested withdrawal rates against historical US stock and bond returns over rolling 30-year retirements. A 4% starting withdrawal, adjusted for inflation each year, survived nearly every historical 30-year period without depleting the portfolio. Since 1 divided by 0.04 equals 25, saving 25x your annual spending is the accumulation-side mirror of the same finding.

The original Trinity Study tested a 30-year horizon, but FIRE retirements are often much longer — someone retiring at 35 might need the portfolio to last 50-plus years. Later research (including updates from the original Trinity authors and others) suggests a lower rate, often 3-3.5%, has historically held up better over multi-decade horizons, while a higher rate can be reasonable for a shorter runway or if you're willing to cut spending in a bad sequence of early returns. This calculator lets you test 2.5% to 5% instead of assuming one number is right for everyone.

No. It's a backtest against a specific, historical dataset — mostly the 20th-century US market — not a mathematical guarantee. It doesn't account for taxes, fees, healthcare cost shocks, Social Security timing, sequence-of-returns risk early in retirement, or the possibility that future long-run returns are lower than the historical sample. Treat the FIRE number as a planning target to revisit periodically, not a number you calculate once and never touch again.

Enter a real (inflation-adjusted) return, since the FIRE number and projection are both in today's dollars. Historically, a diversified US stock-heavy portfolio has returned roughly 5-7% real over long periods; a 60/40 stock/bond mix has run closer to 3-5% real. Using a real return keeps every figure directly comparable to spending you're also thinking about in today's terms.

This calculator assumes you keep contributing every month until you hit your FIRE number. Coast FIRE asks a different question: is your current balance already big enough that you could stop contributing entirely, today, and still reach your FIRE number by a target retirement age purely through growth? See the /coast-fire-calculator/ for that version.