The 4% rule is a 1994 30-year starting rate (Bengen), not a law. Trinity 1998: a 50/50 mix at inflation-adjusted 4% lasted 30 years in 95% of 41 U.S. windows. FIRE lasts 40–50 years. Sequence risk is why a constant real withdrawal can fail when averages look fine.
Four sourced ways to adapt:
- Guardrails (Guyton–Klinger 2006): cut or raise 10% if the current rate drifts ±20%. 5.2–5.6% start, ≥65% equity, 40 years, 99% Monte Carlo confidence.
- VPW: age 40, 60% stocks = 4.1% of this year’s balance.
- Buckets: a cash sleeve. A wrapper, not a fourth engine.
- Floor plus upside (Kitces): lock 3.5–4.0%. Raise only when wealth is clearly ahead.
Write the trigger before a bad year. Run Target FIRE at 3.5%, 4.0%, and 5.2%.