Where does the 4% rule come from and what did the original research actually say?

The 4% rule traces to the 1994 study by financial planner William Bengen and the 1998 Trinity Study by three Trinity University professors. They tested historical U.S. market data and asked what starting withdrawal rate would have survived every rolling 30-year period. The answer was about 4% of the initial portfolio, adjusted upward each year for inflation.

So the rule means: withdraw 4% of your balance in year one, then increase that dollar amount by inflation annually, ignoring later market swings. It assumed a portfolio of roughly 50% to 75% stocks. Importantly, it was designed for a 30-year retirement, not the 40- or 50-year horizons many early retirees face, which is why FIRE planners often trim the rate. Model different rates with wealthserene.com/tools/fire-calculator.