The four per cent rule and what it was actually claiming

The four per cent figure is repeated constantly and understood rarely. Knowing what the original work actually tested makes it considerably more useful.

What the research did

The foundational work asked a specific question: what initial withdrawal rate, adjusted annually for inflation, would have survived every historical thirty-year period using US market data?

The answer, for a portfolio with a substantial equity allocation, was approximately four per cent.

Later work by other researchers examined portfolio composition more thoroughly and reached broadly similar conclusions, with the observation that some equity exposure was necessary — very conservative portfolios failed more often, not less, because they could not outpace inflation over thirty years.

The assumptions that matter

Thirty years. The rule was tested against a thirty-year horizon. Someone retiring at fifty-five with a plausible forty-year horizon is not covered by it, and sustainable rates for longer periods are lower.

US historical data. The twentieth-century United States was among the better-performing markets available. Studies applying the same method to other countries' historical data generally find lower sustainable rates.

This is a substantial caveat. The four per cent figure partly reflects a favourable sample.

Inflation-adjusted constant withdrawals. The method assumes you withdraw the same real amount every year regardless of what markets do.

Almost nobody actually behaves this way. Real retirees reduce spending in bad years, which materially improves outcomes.

No fees. The original work generally used index returns without deducting investment costs or advisory fees. Subtracting one per cent in fees reduces the sustainable rate meaningfully.

Success defined as not running out. A plan that ends with one dollar counts as a success, as does one that ends with several times the starting balance. The measure says nothing about whether the money was well used.

Sequence risk, which is the underlying issue

The reason a fixed withdrawal rate is difficult at all.

Two retirees can experience identical average returns over thirty years and have completely different outcomes depending on when the poor years occurred.

Poor returns early, combined with withdrawals, permanently reduce the capital base from which later recovery must occur. The same poor years occurring late do far less damage.

This is why the first several years of retirement carry disproportionate weight, and it is the argument behind most of the mitigation strategies that follow.

The approaches that improve on it

Variable withdrawals. Adjusting the amount taken based on portfolio performance, within defined limits.

Several published approaches formalise this — reducing withdrawals after poor years and permitting increases after good ones, with rules governing how large the adjustments are.

These generally support higher average withdrawals than a fixed rule, at the cost of variable income.

Guardrails. A specific variant where the withdrawal amount is adjusted only when the withdrawal rate drifts outside a defined band.

This produces stable income most of the time with occasional adjustments, which many people find more tolerable than annual variation.

A cash reserve. Holding one to three years of spending in cash or short-term instruments, to avoid selling equities during a decline.

The theoretical benefit of this is debated — the cash drag has a cost — and the behavioural benefit is real, since it makes it easier not to sell at the wrong time.

Separating essential from discretionary. Covering essential spending with guaranteed income sources and funding discretionary spending from the portfolio, where it can be reduced without hardship.

What figure to actually use

A reasonable planning range for a thirty-year horizon, after fees, with some flexibility, is somewhere between three and a half and four and a half per cent.

Lower for longer horizons, higher fee structures, or plans with no spending flexibility. Higher where there is substantial guaranteed income and genuine willingness to adjust.

What is not defensible is treating any figure as a guarantee. It is a planning assumption to be reviewed annually against what has actually happened.

General information only, not financial advice. Past market performance does not predict future results — consult a qualified adviser about your own situation.