The 4% rule and its limits

The 4% rule says: withdraw 4% of your portfolio in year 1 of retirement, then adjust that dollar amount for inflation each year. Based on US historical data, this withdrawal rate survived every 30-year retirement window from 1926 onward, even including the Great Depression.

The origin

The rule comes from the Trinity Study (Cooley, Hubbard, Walz, 1998), which ran thousands of historical back-tests on different withdrawal rates and asset allocations. For a 50/50 stock/bond portfolio over 30 years, 4% had roughly a 95% success rate. It was a rule of thumb, not a guarantee.

Why it might be too high

• US market returns over the 20th century were historically exceptional — other developed markets produced lower results.
• If you retire at the start of a bad decade for stocks, sequence-of-returns risk can blow up the math (more on that elsewhere).
• Many people want retirement to last 40+ years, not 30. Longer horizons need lower withdrawal rates (3.3–3.5% is a common 'perpetual' number).

Why it might be too low

• The rule assumes you never adjust spending. In reality, people can cut back in bad years and add in good years.
• Social Security replaces part of your income, so your portfolio doesn't need to cover everything.
• Most 30-year simulations end with way more money than they started with — 4% was the floor, not the median.