StrategyIntermediate· 8 min read

The 4% rule, and what it actually promised

The one thing to remember

The rule says a portfolio survived 30 years in the worst historical case. It does not say your money will last forever.

The question

Use the rule as the rough guide it is, rather than the promise it is not.

Figure

The same argument as the text, as a chain. Each step is what makes the next one possible.

Figure

Both lines earn the same 8%. One pays 0.07% a year, the other pays 2%. The gap is not a rounding error, it is most of the point of the exercise.

1
What the research actually said
Withdraw 4% of the starting value, raise it with inflation each year, hold a balanced portfolio, and historically you would not have run out of money over a thirty-year retirement, including if you retired at the worst possible moment.
2
Read the conditions, because they are load-bearing
Thirty years, not forever. A specific mix of shares and bonds. US historical data, which was an unusually good century. And no fees, which do not exist in real life.
Change any one of those and the number moves, sometimes a lot.
Retire early and 'thirty years' is not your horizon. A forty or fifty year retirement is a materially different and harder problem.
3
Rigid withdrawal is the flaw
The rule assumes you take the same real amount whatever happens. Real people can spend less in a bad year, and that flexibility is worth more than any amount of clever asset allocation. A small, temporary cut early on dramatically improves the odds.
4
So treat it as a starting estimate and revisit it
It is a superb rule of thumb for working out roughly how much you need to retire. It is a poor instruction manual for the thirty years afterwards, and it was never intended to be one.

Try it

Compound interest simulatorInteractive

Compounding Without compounding

Starting amount1000 £

Added each month200 £

Annual return7%

Years30

You put in

£73,000

Growth

£179,111

Final

£252,111

Drag the years slider. Notice the curve barely lifts for a decade, then goes near vertical. That is why starting early matters more than the rate.

You have got it when

You can say what your withdrawal rate would be, and what you would cut in a bad year.

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