Dynamic withdrawal rules: guardrails, percentage-of-portfolio, floor-and-ceiling and CAPE-based rates compared
Apply four dynamic withdrawal rules to the same bad year, compare what each tells you to spend, and understand the trade-off between income stability and portfolio safety.
What you will learn
- How percentage-of-portfolio, floor-and-ceiling, Guyton-Klinger guardrails and CAPE-based rates are defined.
- What each rule tells the same retiree to withdraw after a 25 percent loss.
- The trade-off every dynamic rule makes: more stable income means more portfolio risk.
- Rules of thumb for choosing and documenting one rule.
Explanation
The constant inflation-adjusted rule (lesson 2) ignores the portfolio after day one. Dynamic rules let the withdrawal react to markets, the natural answer to sequence risk (lesson 3). The price is a less predictable income.
1. Percentage-of-portfolio. Withdraw a fixed percentage, for example 4 percent, of the current value each year. The portfolio can never be exhausted, but income swings with the market: a 30 percent fall means a 30 percent income cut.
2. Floor-and-ceiling. Start with the percentage-of-portfolio amount, but limit the yearly change in spending: never more than 5 percent above last year's withdrawal (ceiling) and never more than 2.5 percent below it (floor). This smooths income while the portfolio still steers spending over time; some large fund providers recommend "dynamic spending" in this form.
3. Guardrails (Guyton and Klinger, 2006). Set an initial rate, for example 5 percent, and guardrails 20 percent above and below it (6 and 4 percent). Each year compute the current withdrawal rate: above the upper guardrail, cut the withdrawal by 10 percent; below the lower guardrail, raise it by 10 percent. Skip the inflation increase after a negative portfolio year, and make no cuts in the final 15 years. Because cuts are allowed, a starting rate above 4 percent was historically sustainable in US data; the cuts are the price.
4. CAPE-based rates. CAPE is the cyclically adjusted price-earnings ratio: price divided by ten-year average inflation-adjusted earnings (its use in return estimates is covered in the course Portfolio Construction). A high CAPE has historically been followed by lower returns, so the rate is tied to it. Michael Kitces (2008) suggested, from US history, about 4.5 percent when CAPE is above 20, 5 percent between 12 and 20 and 5.5 percent below 12. A simpler linear rule of thumb is
withdrawal rate ≈ 1.5 % + 0.5 × (1 / CAPE)
which gives 4.83 percent at CAPE 15, 4.0 percent at CAPE 20, 3.5 percent at CAPE 25, 3.17 percent at CAPE 30 and 2.93 percent at CAPE 35. Applied yearly to the current value, it raises the rate after a crash and lowers it after a boom, the opposite of instinct. Look up the current CAPE of the index you hold and treat the formula as a guide, not a law.
Rules of thumb. Split spending into a floor of essential costs and discretionary spending; a rule may only cut the discretionary part. Choose the rule before retirement and write it down with exact thresholds (lesson 13). Test it on paper against a 40 percent fall in year one. Review once a year on a fixed date.
Worked example
Hypothetical example: portfolio €1,000,000, first-year withdrawal €40,000 (4 percent), inflation 2 percent. After a bad year the portfolio stands at €720,000 at the start of year two. What does each rule prescribe? Fees and taxes excluded.
| Rule | Year-two withdrawal | Calculation |
|---|---|---|
| Constant real | €40,800 | €40,000 × 1.02; current rate 40,800 / 720,000 = 5.67 % |
| Percentage-of-portfolio (4 %) | €28,800 | 0.04 × €720,000; a 28 % income cut |
| Floor-and-ceiling (+5 % / −2.5 %) | €39,000 | Target €28,800 is below the floor of €40,000 × 0.975 = €39,000, so the floor applies |
| Guardrails (4 % ± 20 %, 10 % cut) | €36,000 | Negative year: no inflation rise; 40,000 / 720,000 = 5.56 % exceeds the 4.8 % upper guardrail; cut 10 % to €36,000 (5.0 %) |
| CAPE-based (CAPE fell from 30 to 22) | €27,144 | Rate 1.5 % + 0.5 × (1 / 22) = 3.77 %; 0.0377 × €720,000; note that this rule would have started at only 3.17 % (€31,700) at CAPE 30 |
Reading the table: the constant rule protects income and pushes the current rate to 5.67 percent, the danger zone of lesson 3. Percentage-of-portfolio protects the portfolio and cuts income by 28 percent in one year, which few households can absorb. Floor-and-ceiling and guardrails sit in between, with cuts of 2.5 and 10 percent. The CAPE rule is the most conservative at high valuations. Which is "right" depends on how much of the €40,000 is essential spending.
Common mistake
Practice activity
On paper: Karim starts with €750,000 and a 3.6 percent initial rate (€27,000). Guardrails ± 20 percent, cut or raise 10 percent, inflation 3 percent. After a strong first year the portfolio is €900,000. (a) The guardrails. (b) Inflation-adjusted withdrawal and current rate. (c) What does the rule prescribe for year two? (d) What would percentage-of-portfolio at 3.6 percent give?
Show solution
(a) Upper guardrail 3.6 × 1.2 = 4.32 percent; lower 3.6 × 0.8 = 2.88 percent. (b) €27,000 × 1.03 = €27,810; 27,810 / 900,000 = 3.09 percent. (c) Between the guardrails, so no adjustment: withdraw €27,810. The raise would only trigger below 2.88 percent, that is above 27,810 / 0.0288 = €965,625. (d) 0.036 × €900,000 = €32,400, a 20 percent rise that the guardrail rule deliberately does not grant yet.
Limitations: one year only; the "no cuts in the last 15 years" clause and taxes on sales are ignored.
Key takeaways
- Every dynamic rule trades income stability against portfolio safety; there is no free option.
- Percentage-of-portfolio never fails but swings income; floor-and-ceiling and guardrails smooth it with limited cuts.
- CAPE-based rules start lower at high valuations and raise the rate after falls.
- Define essential versus discretionary spending and write the thresholds down before you need them.
Next step
Lesson 5 looks at bucket strategies and cash reserves and tests whether they actually beat plain rebalancing.
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