Will a Total Bond Fund Keep Up With Inflation?

In reply to the previous article about fixed-income options in a low-yield environment, a reader wrote in with the following question:

“Would Vanguard’s Total Bond Market fund (or the equivalent) be expected to match inflation over time?”

For a bond (or bond fund), the best estimate for its expected return is its yield. Right now, the SEC yield for Vanguard Total Bond Market Index Fund is 1.19% You can find this on either the “Overview” or “Price & Performance” tab on the fund’s page on the Vanguard site.

But there are two important points of note here.

First point of note: that’s the expected return over the fund’s average duration. We can click over to the “Portfolio & Management” tab to find the fund’s average duration: 6.5 years. So what we’re seeing here is that the fund’s expected return over the next 6.5 years is 1.19%.

For periods shorter or longer than 6.5 years, there’s a greater degree of uncertainty about what the actual return will be.

For shorter periods, 1.19% is still probably the best expected return estimate, but the actual return is going to be primarily affected by price movements (i.e., whether the bonds’ prices move up or down as a result of interest rate changes). See any of the following articles for a discussion of how bond prices respond to changes in interest rates:

• Bond Duration
• What Happens to Bond Funds When Interest Rates Go Up?
• Why Do Longer-Term Bonds Have Greater Price Volatility?

For longer periods, 1.19% is (again) likely the best guess, but we (again) have a lower degree of certainty. In this case, a major cause of the uncertainty is that, as we look at longer and longer periods, we simply don’t know what bonds are going to be in the fund’s portfolio. For example, imagine that we were concerned with the expected return over the next 20 years. Given the fund’s average effective maturity of 8.5 years, most of the bonds currently held by the fund will have matured before the 20-year period is even halfway over. In other words, the return earned by the fund over the next 20 years will be hugely affected by the yields on bonds that it hasn’t even bought yet — and which haven’t even been issued yet. And since those bonds don’t even exist yet, we have absolutely no way to know what their yields will be.

Second point of note: because this is a nominal bond fund, the 1.19% figure is a nominal yield (i.e., before inflation) and therefore a nominal expected return.

A good way to get a rough estimate of the market’s expectation for inflation over a given period is to find the difference in yields between TIPS and nominal Treasury bond for the period in question. For example, since our expected return is for a 6.5-year period, we could look at the yields for 7-year TIPS and 7-year Treasuries. Right now, the yield on 7-year TIPS is -1.10%, and the yield on 7-year Treasuries is 0.55%. That’s a difference of 1.65%, which tells us that the market is expecting inflation of roughly 1.65% over the next seven years.

So, in summary, with an expected nominal return of 1.19% over the next 6.5 years and expected inflation of roughly 1.65% over the next 7 years, we can say that the expected return for Vanguard Total Bond Market Index Fund is about 0.46% below inflation over the next 6.5 years.

But that’s just an expected return. The actual nominal return could be meaningfully different from the 1.19% figure. Or inflation could be meaningfully different from the 1.65% figure. And as discussed above, for periods shorter or longer than 6.5 years, there’s an even greater degree of uncertainty.