The 4% Rule Isn’t a Plan. It’s a Worst Case Number.

If your advisor told you your retirement plan had a 90 percent chance of success, what would you think? Most people feel pretty good about 90 percent. It sounds like a strong grade. It sounds like permission to relax. But 90 percent chance of what, exactly?

A score is not directions

Imagine you fly into a city you have never been to, rent a car, and type your hotel into the app. Instead of directions it tells you that you have a 90 percent chance of arriving on time. You would be frustrated, and rightly so. That is not what you asked for. You wanted directions, not odds.

A probability of success is a score. It tells you the odds. It never tells you what to do next.

What the software means by success

Inside that planning software, success has exactly one definition. You did not run out of money before you died. That is the whole test.

So what is the surest way to pass it? Spend as little as humanly possible. Which means a 100 percent chance of success is also a 100 percent chance of underspending, and nobody ever describes it to you that way.

Where the 4 percent rule actually came from

The famous 4 percent figure was never designed as a spending plan. It was the answer to a worst case question, built to survive the worst starting years in the historical record. Using a worst case number as your everyday budget means living your whole retirement as though the worst case already happened.

Go deeper

Can bucket or guardrail strategies prevent spending cuts?

Is the 4% rule still safe?

Everything on this page is illustrative and hypothetical as of August 2026. It is education, not investment, tax, or legal advice. Any people shown are examples, not real clients, and your situation will differ. Withdrawal-rate rules of thumb are general guidance from published research and are not a prediction or a promise of any result. Protected Lifetime Income figures rely on the claims-paying ability of the issuing insurance company. Kurt H. Jackson is Life and Health Insurance Licensed in MO, NE, KS, IA, and FL, and is not a securities broker, registered investment advisor, or CPA.

Browse all of Kurt’s retirement videos on the Retirement Planning Videos page.