Harvesting Gains from a TIPS ladder

I received this question as a comment to a past blog entry:

Very interesting discussion. One of the assets you mention for constructing the "floor" is a ladder of TIPS. A question about that:

What do you do when the TIPS you are holding increase significantly in value, as they would have done in 2011 for no particular reason (certainly not inflation)? Do you continue to hold them till maturity, or do you do something to harvest your good fortune?

Charlie B

Here is my answer (and please feel free to add comments):

Let me preface this with: I am not a financial planner, so this is just my opinion, and also you may have some unique circumstances which call for another answer...

But generally, I would advise against trying to harvest gains from your bond ladder.

You must have created a TIPS bond ladder because you wanted to safely protect a floor of spending.

By selling it off and not keeping it until maturity, you expose yourself to risk. If you sell and interest rates go up, then you will benefit from the move. But if you sell and interest rates go down, then you will lose from the move. That's because, you still want to protect your income floor, and rebuying the bond ladder after further interest rate declines will become even more expensive and you will be ensured a reduction to your future spending.

I think TIPS yields are just as likely to continue going down, as to go up. That's not a prediction, I'm just saying I wouldn't be surprised if TIPS yields continue decreasing. I wrote about this in a column at Advisor Perspectives:

Are TIPS Really Safe and Worry-Free?

When you talk about harvesting gains, you still have to buy something. TIPS have gained, but likewise any other fixed income product that you might switch to will also be rather expensive, so you don't get any particular benefit from the move.

You are just adding risk when you don't need to.

You were specifically talking about a TIPS ladder. If you own a TIPS mutual fund and it has grown to represent a higher percentage of your assets than you desired to have, then rebalancing some by selling some of the TIPS fund is no problem. But I don't think you were talking about this.

The Trinity Study and Portfolio Success Rates

The other main retirement planning study from the 1990s to enter the retirement research canon came four years after William Bengen’s initial work. The Trinity Study, a nickname for the article, “Retirement Spending: Choosing a Sustainable Withdrawal Rate,” by Philip L. Cooley, Carl M. Hubbard, and Daniel T. Walz (all professors at Trinity University in Texas), appeared in the February 1998 issue of the Journal of the American Association of Individual Investors. The innovation introduced in the Trinity study is ‘portfolio success rates.’ The authors updated their findings from time to time, most recently in the article, “Portfolio Success Rates: Where to Draw the Line” from the April 2011 Journal of Financial Planning.

Before proceeding any further, something must be clear. I will be discussing many different studies, each of which tends to come up with slightly different numbers. This is simply because they use different data sources or make different assumptions.

The only difference in assumptions between William Bengen’s work and the Trinity study regards the choice of bond indices. While Mr. Bengen’s original research combined the S&P 500 index with 5-year intermediate term government bond returns, the Trinity Study used long-term high-grade corporate bond returns instead. The different choice for bonds explains why the worst-case scenario for Mr. Bengen (his SAFEMAX) was a withdrawal rate of 4.15%, but why the original Trinity Study found that a 4% withdrawal rate only had a 95% success rate (with more volatile corporate bonds, the sustainable withdrawal rate dipped below 4% in 1965 and 1966).

Since keeping volatility low is just as important as obtaining high returns, I do think it makes more sense to use intermediate term government bonds than to use corporate bonds. So my re-creation here will follow Mr. Bengen’s choice and will also include the assumption that withdrawals are made at the start of the year rather than the end of the year.

William Bengen’s research gave us the SAFEMAX, which he defined as the highest sustainable withdrawal rate in the worst-case scenario from rolling periods of the historical data. The Trinity Study went a step further by tallying up the percentage of times that withdrawal rates fell below or above certain lines.

They calculated these portfolio success rates for different withdrawal rates (between 3 and 12 percent, both on a fixed and inflation-adjusted basis) and for different time horizons (15, 20, 25, and 30 years) and for different asset allocations (stock allocations of 100, 75, 50, 25, and 0 percent large-capitalization stocks, with the remainder in high-grade long-term corporate bonds).

To understand what they did, again consider Figure 2.1:

What is the success rate for a 5% inflation-adjusted withdrawal rate over a 30-year period with a 50/50 asset allocation?  Well, there are 56 rolling 30-year periods starting between 1926 and 2010.  These rolling 30-year periods begin in the years 1926 through 1981. Nothing is known yet for the 30-year results of more recent starting periods.  Of these 56 rolling periods, we can count up in Figure 2.1 the number of times that the withdrawal rate is above 5%. It is 37 times. That means the portfolio success rate is 100 x 37 / 56 = 66%. I’ve highlighted that number in yellow in the following Table 2.1, which shows the results for many other cases as well. And that is the Trinity Study. I’m not sure how particularly useful this table is for planning future retirements (more on that later), but enjoy looking at Table 2.1 nonetheless: