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What’s the Point of Bonds in a Portfolio? (And Why Individual TIPS, Held to Maturity, Are Unique)

Broadly speaking, bonds can be used to perform either of two distinct roles in a portfolio.

The first role: they are the “thing in the portfolio that’s safer than stocks but which still generally provides more return than cash.”

And for that role, as long as you stay away from bonds that are so risky that they actually aren’t safer than stocks (i.e., bonds with super long durations or extremely poor credit ratings), just about any bonds can do the trick. You can use individual bonds or a bond fund. And as long as it’s low-cost, any of several different types of bond fund would be fine:

  • Short-term Treasury fund,
  • Intermediate-term Treasury fund,
  • Total bond market fund,
  • Short-term TIPS fund, or
  • Intermediate-term TIPS fund.

Any of those will work. The intermediate-term funds are riskier than the short-term funds, and a “total bond” fund is riskier than a Treasury fund, but that, in itself, is neither good nor bad. We can adjust the overall risk level to whatever we want it to be by adjusting the overall stock/bond allocation as needed.

The second role that bonds can play is that they can be used to offset specific costs at a specific date in the future. (“Asset-liability matching” is the technical term for this concept.) For instance, if I expect my first year of retirement to be 10 years from now, and I want to have $60,000 of spending power available in that year, I could buy bonds that mature in that year, to provide me with a very safe way of satisfying that spending.

But here’s the key point: for this purpose (asset-liability matching), it is only individual TIPS, held to maturity, that can do the job.

It has to be TIPS* (rather than “nominal” bonds, which are not adjusted for inflation), because we want a certain amount of purchasing power at some point in the future, rather than a certain dollar amount.

And it must be individual TIPS, rather than a TIPS fund.** And that’s because the only way to have a certain amount of known spending power at some specific date in the future is to hold the TIPS to maturity. With a typical bond fund, the fund is constantly buying new bonds. (It must. Otherwise it would eventually hold nothing but cash as the bonds matured.) And as a result, whenever you sell shares of a bond fund, you’re effectively selling bonds prior to maturity. And so, at the time you buy the fund, you don’t know what it will be worth when you eventually sell it. (For example, if I knew that I wanted to have $10,000 of spending power 10 years from now, a TIPS fund doesn’t achieve that goal for me, because I don’t know what the fund will be worth 10 years from now.)

*I Bonds also work, though they have two major limitations in that they cannot be purchased inside retirement accounts and you’re limited to $10,000 per purchaser per year.

**One exception: BlackRock does offer ETFs that hold TIPS to maturity. For example, iShares iBonds Oct 2028 Term TIPS ETF (IBIE) owns nothing other than TIPS maturing in 2028. And the ETF will hold those TIPS until they mature, and then the fund will liquidate, distributing cash to shareholders. So it works very similarly to just buying 2028 TIPS on your own and holding to maturity.

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