Where the 4% Retirement Rule Came From

The 4% rule often sounds like a verdict: spend more and you are reckless; spend less and you are safe. It is more useful as a starting point with a clearly defined set of assumptions. In his 1994 study, William Bengen tested retirement withdrawals against historical U.S. stock and bond returns and inflation. The question was whether a portfolio could support roughly 30 years of spending when the first withdrawal was a percentage of the initial balance and later withdrawals rose with inflation. His most difficult historical starting periods supported an initial rate of about 4.15%, commonly rounded to 4%.

That method is easy to misread. With a $1 million portfolio, the first year’s withdrawal would be $40,000. If inflation were 3%, the planned second-year withdrawal would be $41,200. It would not automatically become 4% of whatever balance remained after a market decline. Maintaining the spending amount in real terms is exactly what makes a bad opening stretch so consequential.

The order of returns matters

Imagine two portfolios with the same long-run average return. One rises early and falls later; the other falls sharply just as retirement begins, then recovers. A working investor who makes no withdrawals may see similar long-run results in both cases. A retiree must sell assets to pay bills. In the second scenario, those sales occur while prices are low, leaving fewer shares to participate in the recovery. This is sequence-of-returns risk.

It explains why a high average market return does not, by itself, justify a high fixed withdrawal rate. Markets do not deliver their average return every January. It also explains why a historically cautious rate may leave some retirees with far more money than they intended. A rule built to survive difficult starting years will often look conservative in easier ones.

Put the rule inside a household plan

The rule is about an investable portfolio. Home equity cannot pay a grocery bill until it is accessed or a home is sold. Rental property needs its own cash-flow forecast: rent less vacancy, maintenance, insurance, property taxes, and debt service, followed by realistic sale costs and taxes if a sale is planned. Social Security belongs on the timeline at the ages when benefits are expected to begin; the Social Security Administration offers personalized estimates.

A stronger retirement plan maps investable assets, income, spending, taxes, health costs, and possible property sales year by year. Then it tests uncomfortable possibilities: poor returns early on, higher inflation, or a longer life than expected. It also identifies spending that could be reduced temporarily if markets fall and spending that could rise if the portfolio does well.

The lasting lesson of the 4% rule is that average returns are an incomplete retirement plan. The number is neither a guarantee nor a universal ceiling. Understand the time horizon, assets, and withdrawal pattern behind it before deciding how much weight to give it in your own household.