What Is MUB? iShares National Muni Bond ETF

MUB is the iShares National Muni Bond ETF from BlackRock. It tracks the ICE AMT-Free U.S. National Municipal Index and holds thousands of investment-grade municipal bonds issued by states, cities, and local authorities across the country. The expense ratio is a very low 0.05%.

The defining feature of MUB is tax treatment. The interest municipal bonds pay is generally exempt from federal income tax, which makes MUB most valuable to investors in high tax brackets. Its stated yield near 3.4% therefore understates its appeal: on an after-tax basis, that income can beat a taxable bond fund yielding significantly more.

Approximate weights as of mid-2026; refresh quarterly from BlackRock iShares's fund page. Each ticker links to its individual stock guide in Walnut.

MUB holds thousands of investment-grade municipal bonds spanning general obligation and revenue debt from states, cities, school districts, and other local authorities. Large issuing states like California, New York, and Texas make up sizable portions simply because they borrow the most. The fund excludes bonds subject to the alternative minimum tax, and no single issuer dominates, so default risk is spread widely.

Two numbers matter for understanding the sleeve. The credit quality is investment grade, so default risk is low but not zero. The effective duration is about 6 years, which means MUB carries real intermediate-term interest-rate risk, comparable to a mainstream taxable bond fund. The tax advantage does not remove the price sensitivity to rates.

The right way to compare MUB with a taxable bond fund is the tax-equivalent yield. That figure converts MUB's tax-exempt yield into the taxable yield you would need to match it after taxes. If MUB yields 3.4% and you are in the 37% federal bracket, the tax-equivalent yield is roughly 5.4%, since 3.4% divided by (1 minus 0.37) equals about 5.4%.

This is why the audience for MUB is specific. A high-bracket investor holding bonds in a taxable account often nets more from MUB than from a higher-yielding taxable fund. A low-bracket investor, or anyone holding bonds inside an IRA or 401(k) where the tax shelter is already built in, usually does better with taxable bonds, because MUB's exemption is wasted there.

MUB's return combines its tax-exempt coupon income with price swings driven by interest rates and, to a lesser degree, muni credit conditions. Its intermediate duration meant it fell during the 2022 rate spike, like most bond funds, then recovered as conditions stabilized. Its steady tax-free income is the main draw for long-term holders.

The outlook depends on the direction of interest rates and the health of state and local finances. If rates fall, MUB's price tends to rise; if they climb, its intermediate duration works against it. Muni defaults have historically been rare among investment-grade issuers, so the dominant risk for MUB is rates rather than credit.

MUB fits high-bracket investors who want federally tax-exempt income inside a taxable account and can accept intermediate-term price movement. It is often used as the bond sleeve for taxable savings, where the tax exemption does real work. It is less useful in a retirement account, where a taxable bond fund typically delivers more after-tax income.

The tradeoffs are its rate sensitivity from a duration near 6 years and the fact that its benefit hinges entirely on your tax situation. Walnut is not an investment adviser and this is not a recommendation. Whether MUB suits you depends on your federal tax bracket, the type of account you would hold it in, and your tolerance for interim price swings.

MUB trades like any stock during market hours on brokers such as Robinhood, Fidelity, Schwab, and Public, many of which support fractional shares so you can invest a set dollar amount. As the largest muni ETF, it typically trades with tight spreads and deep liquidity.

If you hold other positions elsewhere, you can connect your brokerage to Walnut to track MUB alongside the rest of your portfolio and see how your tax-exempt bonds fit your overall allocation across taxable and tax-advantaged holdings. Trade execution always stays at your own broker; Walnut is the tracking and analysis layer.

MUB is a broad, low-cost municipal bond ETF whose federally tax-exempt income makes it most valuable to investors in high tax brackets. Its headline yield near 3.4% understates its appeal: the tax-equivalent yield can top 5.5% for top-bracket earners. With a duration near 6 years it carries intermediate rate risk. It plays a tax-efficient bond-sleeve role, best suited to taxable accounts.

Whether MUB is worth buying today depends more on your time horizon and what you already hold than on any single call. We walk through valuation, concentration, and what would have to be true for it to outperform from here in is MUB a buy?

MUB yields ~3.4% (30-day SEC yield, federally tax-exempt; tax-equivalent ~5.5%+ for top brackets) as of mid-2026, paid by passing through the dividends of its underlying holdings. For the payout schedule, history, and how the distributions are taxed, see MUB dividend: yield and schedule.