How this calculator works
Your FIRE number is annual spending ÷ withdrawal rate. At the classic 4% rate that means 25× your yearly costs; at a more cautious 3.5% it's about 29×. The timeline then simulates your portfolio month by month — existing investments growing at your expected return, plus your monthly contributions — until it crosses that line.
The 4% figure comes from research on US market history — William Bengen's 1994 study and the later "Trinity study" — which found that an initial 4% withdrawal, adjusted for inflation, survived most historical 30-year retirements. It is a rule of thumb built on one country's past, not a law of nature: many planners today test 3–4%, and longer retirements argue for the lower end.
Common questions
What is a FIRE number?
The portfolio size at which investment withdrawals could cover your living costs indefinitely, making paid work optional. It is usually calculated as annual expenses divided by a safe withdrawal rate — 25 times annual spending at the common 4% rate.
Is the 4% rule safe?
It is a research-based rule of thumb, not a guarantee. It came from studies of US historical returns over 30-year retirements. For earlier retirement, longer horizons, or non-US portfolios, many people test 3–3.75% instead. Lower withdrawal rates mean bigger targets but more resilience.
Should I use spending or income?
Spending. Your portfolio has to replace what your life costs, not what your employer pays. Most people spend meaningfully less than they earn, so using income inflates the target and the years to reach it.
What return should I assume on the way there?
Long-run global equity returns have averaged roughly 5% a year after inflation, with US markets historically higher in nominal terms. Testing 5–8% covers a sensible range; using after-inflation returns with today's spending keeps the whole calculation in consistent, real terms.
This tool is educational and not financial advice. Withdrawal-rate research is based on historical data and mostly US markets; your future will differ.
- 1.Determining Withdrawal Rates Using Historical Data (origin of the 4% rule) — William Bengen, Journal of Financial Planning, 1994
- 2.Trinity study (retirement savings withdrawal rates) — Cooley, Hubbard & Walz — overview, 1998