Also called: Drawdown phase, Spend-down.
Accumulation and decumulation are different problems that happen to involve the same portfolio. Saving is forgiving: volatility helps, mistakes have decades to be absorbed, and the main variable under your control is the savings rate. Spending is unforgiving in every one of those respects.
The reversal is what catches people. In accumulation a crash means buying at lower prices. In decumulation it means selling at lower prices, permanently, to fund this year’s spending. The same event flips from opportunity to damage.
Decumulation also introduces decisions that simply do not exist while saving: the withdrawal rule, the order accounts are drawn from, how much cash buffer to hold, and when to take state or workplace pensions. Several of those are irreversible.
The industry has spent far more effort on accumulation than on this phase, which is why the tooling is thinner and the rules of thumb are shakier. It is also why testing a spending plan against real market history and against thousands of simulated ones is worth more here than anywhere else.
Research on this
- Is the 4% Rule Still Safe? We Ran 5,000 Simulated Retirements
- Sequence of Returns Risk: What If the Market Crashes the Year You Retire?
See also
- Sequence of returns risk — The risk that the order in which investment returns arrive damages a plan, even when the average return is unchanged. It matters most when money is being withdrawn.
- Safe withdrawal rate — The share of a portfolio’s starting value you can withdraw in year one of retirement, then raise with inflation each year, without running out over your horizon.
- Guardrails (Guyton-Klinger) — A withdrawal policy that starts from fixed spending, then cuts it when the withdrawal rate breaches an upper band and raises it when it falls below a lower one.
- Ruin rate — The share of runs in which a plan exhausts its portfolio before the horizon ends. A 5% ruin rate means the money ran out in one simulated run in twenty.