Forget AGG in Retirement. MUB Does the Same Job With a Smaller Tax Bill

Most retirees holding bonds in a taxable brokerage account default to the same broad bond ETF they've always used, but that habit quietly hands a chunk of their income back to the IRS every single year.

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The Bloomberg U.S. Aggregate Bond Index is essentially the S&P 500 of the bond market. It provides broad exposure to the U.S. investment-grade fixed-income universe, including Treasury bonds, agency mortgage-backed securities, and investment-grade corporate debt across a range of maturities. For decades, it has been the default benchmark for investors who simply want their bond allocation to behave like the overall bond market.

The iShares Core U.S. Aggregate Bond ETF (AGG) packages that benchmark into a single diversified ETF. That’s appealing for retirees because you get thousands of bonds, regular income, high overall credit quality, and exposure to both government and corporate debt without having to build and maintain a bond ladder yourself.

The issue for retirees holding bonds in a taxable brokerage account is that diversification doesn’t necessarily translate into tax efficiency. Much of the income generated by an aggregate bond ETF remains taxable, and fixed income generally has less expected return than stocks to absorb that tax drag. For the right investor, I think a national municipal bond ETF can perform a similar portfolio role while potentially leaving more of the income available to spend.

Municipal bonds are issued by states, cities, counties, and other government-related entities to finance public expenditures. General obligation bonds are generally backed by the taxing authority of the issuer. Revenue bonds are instead supported by cash flows from a specific project or source, which could include toll roads, airports, hospitals, utilities, or public transportation systems.

For taxable investors, the major attraction is how the interest is treated. Interest from qualifying municipal bonds is generally exempt from federal income tax. That contrasts with corporate bond interest, which is generally federally taxable as ordinary income. Treasury interest is also federally taxable, although it generally receives an exemption from state and local income taxes.

There are exceptions to consider. Certain private activity municipal bonds can create exposure to the alternative minimum tax (AMT). Investors specifically concerned about AMT exposure should therefore check a fund’s mandate and holdings rather than assuming every municipal distribution receives identical treatment.

Municipal bonds also carry credit risk, but broad national muni portfolios tend to maintain relatively high overall credit quality. That makes them particularly interesting for retirees who aren’t necessarily trying to maximize yield, but instead want diversification, income, and a potential counterweight to equities.

The iShares National Muni Bond ETF (MUB) is one of the simplest ways to implement this strategy. It provides broad exposure to the investment-grade U.S. municipal market rather than concentrating on a single state. MUB charges a 0.05% expense ratio and currently offers a 3.84% 30-day SEC yield.

Looking only at that yield can make the fund appear less attractive than a taxable aggregate bond ETF. The more useful comparison in a taxable account is its tax-equivalent yield. This estimates how much a taxable bond investment would need to yield for an investor to retain the same income after federal taxes.

MUB’s current estimated tax-equivalent yield is 6.49%. In other words, for an investor subject to the max federal income tax rate assumed in that calculation, a taxable bond fund would need to yield approximately 6.49% to match MUB’s 3.84% federally tax-exempt yield after taxes.

That’s why I think retirees should be careful about automatically defaulting to AGG. AGG remains an excellent broad bond ETF, particularly inside an IRA where its distributions aren’t creating an annual taxable-income problem. But taxable brokerage accounts change the calculation.

MUB can provide many of the characteristics retirees actually want from fixed income, including diversification, relatively high credit quality, income, and lower volatility than equities, while potentially reducing the federal tax bill attached to those distributions.

It’s not an identical replacement because AGG has substantial Treasury and agency mortgage exposure. But for a retiree using bonds primarily for income and portfolio stability in a taxable account, I’d pay close attention to what remains after taxes rather than simply buying whichever ETF best represents the overall bond market.

Contact [email protected] for any questions or corrections.

Tony Dong is the founder of ETF Portfolio Blueprint. He also serves as Lead ETF Analyst for ETF Central, a partnership between Trackinsight and the NYSE.

Tony’s work focuses on ETF strategy, portfolio construction, and risk management, with an emphasis on making complex investment concepts accessible to everyday investors. His insights and analysis have also appeared in U.S. News & World Report, Kiplinger, MoneySense, and The Motley Fool.

Tony holds a Master of Science degree in enterprise risk management from Columbia University and the Certified ETF Advisor (CETF) designation from The ETF Institute.

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