How long will your money last? See your runway at any withdrawal rate.
Uses a single deterministic return rate. Real markets have sequence-of-returns risk: a 30% drop in year 1 of retirement is far more damaging than the same drop in year 20, even at the same average return. The 4% rule (Trinity Study) assumed a 50/50 stock/bond portfolio over 30 years. For aggressive withdrawal rates above 4%, run a Monte Carlo simulation before acting.
