The safe withdrawal rate (SWR) is the percentage of your portfolio you can withdraw annually without running out of money. It determines your FIRE number. Here's everything you need to know.
If you have a $1,000,000 portfolio and withdraw $40,000/year, your withdrawal rate is 4%. The "safe" part means your portfolio historically survives this rate indefinitely — it doesn't run out, even across 30-year historical periods including market crashes.
The 4% rule was calibrated for 30-year retirements. If you retire at 35 and live to 90, you need your money to last 55 years. Historical data is thinner for such long periods, and some researchers argue 3–3.5% is more appropriate. The longer your expected retirement, the more conservative your withdrawal rate should be.
The 4% rule assumes fixed inflation-adjusted withdrawals every year. In practice, most retirees reduce spending in bad market years and increase it in good ones. This flexibility dramatically improves portfolio survival rates — a "guardrails" strategy (reducing spending if the portfolio drops below a threshold) achieves success rates over 95% even at higher withdrawal rates.