The Ultimate Guide to Safe Withdrawal Rates – Part 11: Six Criteria to Grade Withdrawal Rules

After a three week hiatus from our safe withdrawal rate research, welcome back to the next installment! If you liked our work so far make sure you head over to SSRN (Social Science Research Network) and download a pdf version. It’s a free 47-page (!) pdf working paper covering parts 1 through 8:

Our SSRN working paper

But let’s move on to part 11. In our previous posts (Part 9 and Part 10), we wrote about the Guyton-Klinger dynamic withdrawal rule and why we’re not great fans. Add to that our two-month-long bashing of the static 4% rule and people may wonder:

What withdrawal rule do we like?

True, we proposed a lower initial withdrawal rate (3.25-3.50% depending on future Social Security income), but that’s just the starting point. We have written here and elsewhere that this withdrawal rate is not set in stone. How do we go about adjusting the withdrawals in the future? How did different dynamic withdrawal rules perform in the past? How do we even measure how much we like a withdrawal rate rule? Today, we like to take a step back and gather a list of criteria by which we like to evaluate different (dynamic) withdrawal rules. Then simulate a bunch of withdrawal rules and assign grades.

Withdrawal rate rules we consider

1. The Fixed 4% rule: Set the initial withdrawal amount to 4% of the portfolio and then adjust by the CPI every month.
2. Guyton-Klinger with a 4% initial rate. +/-20% guardrails and 10% adjustments. For a primer on what this rule does and some of the skeletons in the closet, check our previous posts on that topic, Part 9.
3. The same Guyton-Klinger rule but with a 5% initial rate.
4. Constant percentage: withdraw a fixed 4% p.a. of the portfolio over time (i.e., 0.333% each month).
5. The Variable Percentage Withdrawal (VPW) rule, see the Bogleheads link on this, assuming a 40-year retiree (mid-point between Mr. and Mrs. ERN’s age at our planned retirement date). The same mechanics as the constant percentage, though we start at 4.6% and increase the rates based on the remaining life expectancy, calculated by smart folks at Bogleheads. In our simulations we cap the withdrawal rates at 8%, though, to ensure we don’t deplete the principal in year 60. We still like to leave a nice size bequest.
6. A rule based on the Shiller CAPE: Calculate the Cyclically-Adjusted Earnings Yield (=1/CAPE) and use this as a proxy for expected equity returns. Then set the withdrawal rate to W = a + b*CAEY with the appropriate parameters for a and b. The first time I encountered this rule was at the cFIREsim site where they use this exact parameterization as their default values: a=1% and b=0.5. (There is some science behind the parameter choice and we will deal with the details in a later post!)
7. Same as 6 but with a=1.5%, i.e., shift up the withdrawal rate in 6 by another 0.50% p.a.
8. Same as 7 but with a=2.0%.

 Here are our criteria to grade the different withdrawal rules:

1. Respond to changing fundamentals in financial markets and the economy
2. Provide guidance on the appropriate initial withdrawal rate
3. Withdrawal amounts should display low short-term volatility.
4. Withdrawal amounts don’t suffer significant and long-lasting drawdowns. 
5. Withdrawals have the potential to maintain purchasing power over at least 30 years
6. The initial withdrawal amount is not unnecessarily low. 

We will elaborate more below. For now, they should appear pretty intuitive, albeit a bit subjective. For example “low short-term volatility” means different things to different people. We will grade those criteria on a scale A = best, F = worst.

Simulation assumptions

• 80% equity, 20% bond share (S&P500 total return and 10-Year U.S. Treasury Benchmark Bond total return).
• 60 years horizon, with actual returns Jan 1957 – Dec 2016.
• Monthly simulations.

Simulation Results

Apparently, 1957 wasn’t such a bad year to start retirement. At least the 4% rule didn’t run out of money! But also notice the bumpy road during the first 30 years with a significant reduction for most of the withdrawal rules during the 1970s. In the table below we report some more stats on the final portfolio value and the withdrawals over time. Notice that the 4% rule would have accumulated a massive portfolio, more than 4 times the initial size. And that’s adjusted for inflation! So, there was ample opportunity for adjusting the withdrawal amounts upward.

And here’s the Report Card

The summary of the grades we assigned here is in the table above, completely subjective and open for discussion, of course! The explanation of the grades follows.

1: Respond to fundamentals in financial markets

The top performers here are the CAPE-based rules. We set our withdrawal amounts not just based on price movements but also based on economic fundamentals (earnings yield), which earns a big fat A.

The Constant percentage and VPW both get a B because they clearly react to changes in financial conditions. If your portfolio is down by x% your withdrawal amount goes down by roughly x%, so you can’t blame it for not being responsive. But both rules lose some points for chasing price movements only and ignoring economic fundamentals (earnings!). You will overreact with the withdrawal amounts during the late 1990s equity bubble and also slash withdrawals dramatically during an equity market downturn when prices overreact on the downside.

Another notch down is Guyton-Klinger. That rule responds to changing asset prices but potentially with a delay of multiple years. You wait until you hit one of guard rails! Sorry, you get only a C for that. Of course, the static 4% rule gets an F for being completely oblivious to what’s going on in the world out there.

2: Guidance in the initial withdrawal rate

Both the fixed 4% and Constant Percentage 4% rules get a D. The 4% Guyton-Klinger Rule gets a D as well. Just picking some arbitrary percentage number is not sufficient. As we showed before in part 3 of this series, the 4% rule has very different success probabilities depending on where we are in the earnings yield cycle. The Guyton-Klinger rule with a 5% initial rate gets an F for its deceptive marketing. Sorry, but this rule cannot magically generate 1% p.a. excess return (alpha), see our posts from the last two SWR posts, here and here.

The VPW gets a C. It’s still not very good guidance given their percentage is also oblivious to market conditions, such as equity earnings yields and thus runs the risk of being too low if stocks are cheap or too high when stocks are expensive. But the effort of setting the initial withdrawal rate in response to different asset allocations and ages definitely earns the VPW a nice solid C. The CAPE-based rules get a B for at least thinking about different initial equity P/E ratio regimes. But there’s still some ambiguity about what the appropriate values for a and b should be.

3: Short-term Volatility

In retirement, we obviously have some spending flexibility, but we don’t like to go from top to flop, e.g., from a very generous travel budget in one year to a zero travel budget in the next year. We like to keep year over year withdrawal amount fluctuations to a minimum.

The simple 4% rule gets an A for having, well, zero volatility in the withdrawals. Though, when you are unlucky enough to run out of money that would be the mother of all short-term volatility, i.e., -100%. We are generous and decided to penalize the 4% rule grade in categories 4 and 5, not the short-term volatility grade, though.

Guyton-Klinger gets only a C. There is some pretty significant volatility year over year and the worst Y/Y drop is more than 25%. The CAPE-based rules have much more subdued year-over-year volatility, by construction, and get a nice, solid B; a B+ for the less aggressive rule with a=1.0% and a B- for the more aggressive rule with a=2.0%.

Both the constant percentage 4% rule and VPW get a big fat D on this one. Your withdrawal amounts become just about as volatile as your portfolio. And keep in mind that these numbers are already smoothed 12-month average withdrawals. The drawdowns peak to bottom are the same or worse as the portfolio drawdowns. To us, this seems quite undesirable. Of course, someone at the Bogelheads forum seems to claim that the VPW actually smoothes the withdrawal amounts:

“Q: Why not simply use a Constant-Percentage withdrawal instead?
A: Because VPW takes into account your current age, and allows you to eat more and more into your capital, as you age, while trying to smooth out the withdrawals.”

Though the first two claims (taking into account the age and generating an orderly exhaustion of capital all the way to age 100) are true, the VPW doesn’t do much smoothing at all. It’s just as volatile and even slightly more volatile than the Constant-Percentage Rule, and hence gets penalized another notch to a D-! The VPW percentage withdrawals increase over time and, true, if you’re lucky and increase the age-dependent withdrawal rate in a year with negative returns you would cushion the drop a little bit. But if you increase the VPW value in a year with positive returns you’d exacerbate the volatility. Most of the variance in withdrawal amounts still comes from the portfolio returns and, for all practical purposes, this method generates highly volatile withdrawal amounts.

4: No significant drawdowns in withdrawals

This was our pet peeve with Guyton-Klinger. We don’t like a multi-year or even multi-decade reduction in our standard of living. It’s easy to smooth out yearly fluctuations with some smart budgeting and a side gig here and there. But significantly reducing spending for 10-20 years means going back to work. Something we like to avoid.

Well, the 4% rule never has a drawdown until it runs out of money. As we showed in previous posts, the risk of running out of money is a serious concern when targeting 50 or 60-year horizons and considering today’s lofty equity valuations. Only a D grade here. Even though the 1957 starting date saw a great success of the 4% rule!

Guyton-Klinger, the Constant 4% and VPW all get a D on this one. The 5% Guyton Klinger even a D-. Some of the stats like the drawdown peak to bottom are truly scary.

Finally, we were very positively surprised about how smooth the CAPE-based withdrawal amounts were. The drop in withdrawals also lasts long, but it is a lot more shallow than for the other rules. Example: The intermediate rule starts at 4.5 in 1957, goes to a bit over 5.0 during the first decade, drops to 3.6 during the late 1970s and 1980s and then recovers again. During the volatile years since 2000, the declines in the withdrawal amounts were also shallow and short-term in contrast to the other rules. Good job, CAPE! We assign a B, B- and C+ for the three CAPE-based rules.

5: Maintain purchasing power after 30+ years

This one has a similar flavor as item #4 but it still a slightly different animal. We want to avoid a slow and permanent erosion of purchasing power, see illustration below:

The 4% rule has a 2.5% probability of running out of money after 30 years (80% stocks, 20% bonds), but a 37.2% probability of not maintaining 100% of its purchasing power. That doesn’t get you more a D grade in our household, and that’s when we feel generous.

Guyton-Klinger definitely does much better. True, it suffers from potentially year-long, even decade-long drawdowns in withdrawals, but after 30+ years you’re likely back to the initial net worth and the initial withdrawal amounts. In fact, if anything, you might withdraw too little and over-accumulate because the withdrawal rate is likely to be stuck at the lower guardrail. GK gets a nice solid A for the 4% initial rate and a B when starting with a 5% rule.

The constant percentage 4% rule rate gets an A because over the very long haul the expected real return of your 80/20 portfolio is higher than 4%. VPW gets an A as well. It’s obviously designed to exhaust the capital but the withdrawal amounts definitely have an upward moving trend.

The CAPE rules get grades between A- and C, depending on how aggressive you structure the parameters. Especially, the rule with a=2.0% might be a notch too aggressive and could create a slow erosion of real withdrawals over time.

6: The initial withdrawal is not too low

Any rule that withdraws a crazy low initial amount might ace some of the other criteria above but is still useless. All rules with 4%+ initial withdrawal rates clearly pass this criterion. The CAPE rules will likely fall below that 4% withdrawal rate most of the time. They had pretty competitive initial withdrawal rates back in 1957, but today, we’d be looking at only 2.7% when using the most conservative parameters (a=0.01,b=0.50) to 3.7% with the more aggressive parameters (a=0.02, b=0.50). That’s quite unattractive. But intriguingly, the one with parameter a=1.5% generates an initial withdrawal rate almost exactly at the 3.25% we proposed earlier in Part 3, and its overall grade is the highest (tie with a=1.0%). So, this might be something we will apply in our own withdrawal strategy!

Conclusion

Today’s case study taught us a lot. For a change, we intentionally didn’t look at a worst-case retirement date. 1957 was a pretty decent starting date that would have preserved the purchasing power of the classic 4% rule. But the path was rocky! The recession in the 1970s, the dot-com bust, and the Global Financial Crisis would have caused some crazy swings in the withdrawal amounts of the dynamic rules.

The Guyton-Klinger rules, Constant Percentage 4% and VPW all beat the Fixed 4% Rule. The CAPE-based rules perform a lot better at least according to our subjective grading scheme. They may afford a slightly lower initial withdrawal amount but the lower volatility going forward might be worth that cost.

Thanks for stopping by today! Please leave your comments and suggestions below! Also, make sure you check out the other parts of the series, see here for a guide to the different parts so far!