Where does the 4% rule come from?
The 4% rule is the most famous rule of thumb in retirement planning. It says you can withdraw 4% of your portfolio in year one of retirement, then increase the dollar amount by inflation every year after that, and the money will most likely last 30 years. The rule is not a law of nature. It is a summary of historical US market behaviour.
Bengen and the Trinity Study
The rule has two parents. In 1994, financial planner William Bengen published a paper called "Determining Withdrawal Rates Using Historical Data." He tested stock and bond portfolios over US market history and found that a 4% initial withdrawal rate survived 30 years in almost every period. He also found that portfolios with some bonds performed better than all-stock portfolios, because the bonds reduced volatility.
In 1998, three professors at Trinity University published the study that gave the rule its name. Philip Cooley, Carl Hubbard, and Daniel Walz looked at US stock and bond data from 1926 to 1995. They tested withdrawal rates from 3% to 12%, with different stock and bond mixes. Their conclusion: a 4% initial withdrawal, followed by inflation adjustments, survived a 30-year retirement in 95% or more of the historical periods they tested.
The rule applies to the first year only. You withdraw 4% of the starting portfolio. Every year after that, you increase the withdrawal by the previous year's inflation. If the portfolio grows, your spending stays steady in real terms. If the portfolio shrinks, your spending still rises with inflation, which is what makes the rule dangerous in bad sequences.
Why it worked in the US
The US has a long history of strong equity returns. From 1926 to the present, US stocks delivered real returns well above inflation across most rolling 30-year periods. Bonds also did their job, providing stability and rebalancing ammunition. The worst historical periods were the Great Depression and the 1960s-1970s stagflation era. Even then, a 4% withdrawal survived most 30-year windows.
The rule does not work as well in every country. Researchers have tested the same approach using international data and found lower safe rates in markets such as the UK, Japan, and Germany. The US result is partly a result of US exceptionalism, not a universal rule.
Criticisms and updates
The biggest criticism is that the future may not look like the past. US stock valuations were much lower during much of the historical period. Interest rates were higher. A retiree starting in 2000 or 2007 faced a different environment. Sequence-of-returns risk means that the order of good and bad years matters more than the average return.
More recent research suggests that early retirees should use lower starting rates. For a 40 or 50-year retirement, 3.5% or 3.25% is often recommended. Flexible withdrawal rules, such as cutting spending after a bad year, also improve survival rates significantly. Some researchers argue that 4% is still fine for a traditional 30-year retirement, but too aggressive for anyone retiring before 60.
Our calculator lets you test the rule yourself. Set the withdrawal rate to 4%, then move it down to 3.5%. Watch the FIRE number change. The 4% rule is a benchmark, not a guarantee, and the best way to respect it is to understand where it came from.
Last updated: 2026-08-02. This article is educational and is not financial advice.