Comes from the 1998 Trinity Study, which tested historical US stock/bond portfolios over 30-year retirements and found a 4% initial withdrawal, adjusted for inflation each year after, rarely ran out of money. It's a backtest of one country's market history, not a law of finance.

🇵🇹 European and Portuguese market returns don't match the US dataset the study used, and more recent research (including for lower-expected-return environments) often points to a more conservative 3% to 3.5% as a safer starting point outside the US. Confirm current thinking before relying on 4% for a real plan.