A withdrawal rule that adjusts can start higher than one that cannot
The claim
Allowing withdrawals to respond to portfolio performance supports a materially higher initial withdrawal rate than a rule that raises spending with inflation regardless of what the portfolio does.
Why we rate it moderate
Demonstrated repeatedly in historical simulation and consistent across studies, but the size of the gain depends entirely on how much spending flexibility is assumed, and that assumption is rarely tested against how households actually behave.
The classic safe-withdrawal studies fix real spending at the outset and never change it. That assumption is what makes the answer conservative: the rule has to survive the worst sequence in the record while spending as if nothing had happened. No actual retiree behaves that way, and the ones who do would be making a mistake.
Guyton and Klinger formalised the alternative as decision rules: skip the inflation increase after a losing year, cut spending when the withdrawal rate drifts above a ceiling, raise it when the portfolio has done well enough that the rate falls below a floor. Simulated against the historical record, rules of this shape support initial rates well above the rigid benchmark for the same failure probability.
The gain is not free, and it is easy to overstate. It comes entirely from the willingness to spend less in bad states, which is a real welfare cost even when it does not appear as a failure in a simulation. A plan that 'never fails' because it cuts spending 30% in a downturn has not solved the problem; it has relabelled it.
The right way to use this is to separate spending into a floor and a discretionary layer. The floor should be funded by something that does not depend on markets — Social Security, a pension, an annuity, a bond ladder. The discretionary layer can flex, and it is that layer the decision rules should operate on. Stated this way, flexibility becomes a plan feature rather than an assumption smuggled into a simulation.
The corollary matters as much: if your spending genuinely cannot flex, the rigid studies are the right ones for you and the higher rates are not available. Knowing which case you are in is more useful than the third decimal place of any withdrawal rate.
Where this breaks down
- Flexibility is assumed rather than observed in most of this literature. Households facing a bad sequence may find far less of their spending is discretionary than they believed.
- Decision rules require discipline in exactly the conditions that erode discipline. A rule that is abandoned in the drawdown it was designed for is worse than a lower starting rate.
- Higher initial rates concentrate the risk early, where sequence risk is most damaging. The flexibility has to arrive quickly to work.
- Results are US-history-specific in the same way the fixed-rate studies are, and inherit the same optimistic base case.
Sources
Follow these rather than taking our word for the summary.
Jonathan T. Guyton and William J. Klinger (2006). Decision Rules and Maximum Initial Withdrawal Rates
Journal of Financial Planning, March 2006
Finding: Withdrawal rules that suspend inflation increases and adjust spending in response to portfolio performance sustained materially higher initial withdrawal rates than a fixed real rule.
Philip L. Cooley, Carl M. Hubbard and Daniel T. Walz (2003). Comparative Analysis of Retirement Portfolio Success Rates
Financial Services Review, 12(2), 115-128
Finding: Portfolio success rates vary sharply with withdrawal rate, equity share and horizon, with no single rate safe across all combinations.