What is a safe withdrawal rate?

Where the 4 percent rule came from

In October 1994 a financial planner named William Bengen published a study in the Journal of Financial Planning. He took a portfolio split evenly between the S&P 500 and intermediate term Treasuries, ran it through every thirty year retirement window back to 1926, and asked one narrow question. What is the largest first year withdrawal, raised each year with inflation, that never ran out of money in any window?

The answer was 4.15 percent. Bengen called it SAFEMAX. The worst window belonged to someone who retired in 1966, straight into a decade of poor returns and high inflation.

Somewhere between that paper and the internet, 4.15 became 4, and a worst case became a rule.

A floor, not a forecast

This is the part that gets lost. The figure was never a prediction of what your portfolio will support. It was the number that survived the ugliest stretch in the data. In most historical windows a retiree could have taken considerably more and still died with a larger portfolio than they started with.

Planning at the worst case is defensible. Believing the worst case is the expected case is not, and it will keep you working years longer than you needed to.

Why the order of returns decides everything

Two people retire with a million dollars and withdraw fifty thousand a year. Give them the same fifteen annual returns. Give one of them those returns in reverse order.

Same returns. Same average. Same withdrawals. The one who met the bad years first finishes with about $486,546. The one who met them last finishes with about $968,245, close to double.

The mechanism is not mysterious. Selling into a fallen market takes a bigger bite of the shares you hold, and those shares are not there to recover when the market does. While you are still adding money the effect works in your favor. Once you are withdrawing it works against you, hardest in the first few years.

That asymmetry is why retirement math is harder than accumulation math.

Why the number keeps moving

Bengen later raised his own figure to 4.7 percent, which he calls the Universal Safemax, after widening the portfolio to include small cap and international stocks. More diversification bought more room.

Morningstar publishes its own estimate every year and has generally landed lower. They are not contradicting Bengen. They are answering a different question with different inputs, using forward looking return assumptions rather than the historical record, so their number moves with equity valuations and bond yields.

We are deliberately not printing a current figure. Any specific rate published this year gets revised, and a page quoting one becomes wrong quietly. The reasoning is what lasts. Higher valuations and lower yields push the sustainable rate down. A longer retirement pushes it down. Broader diversification and a willingness to adjust spending push it up.

How to actually use this

Pick a rate, understand which assumptions it encodes, then plan to respond rather than comply. Retirees who trim spending a little after a bad year survive scenarios that break a rigid schedule. Flexibility is worth more than precision in the third decimal.

The multiple people reach for follows straight from the rate. At 4 percent you need 25 times your annual spending, because 1 divided by 0.04 is 25. At 3.5 percent the multiple is about 29. At 5 percent it is 20. Choosing a rate and choosing a savings target are the same decision written two ways.