MUB ETF: A Low-Cost, Investment-Grade Municipal Bond Fund for US Market Exposure

The iShares National Muni Bond ETF (MUB) is a low-cost, investment-grade municipal bond fund with $39 billion in assets. It provides broad exposure to the US municipal bond market and is diversified, with nearly 100% of the portfolio being investment-grade.

The iShares National Muni Bond ETF (MUB) is a low-cost, investment-grade municipal bond fund with $39 billion in assets, providing broad exposure to the U.S. municipal bond market. With nearly 100% of its portfolio consisting of investment-grade bonds, MUB offers a diversified and tax-efficient option for investors seeking moderate risk with federal tax-exempt income.

MUB tracks the ICE AMT-Free US National Municipal Index, which includes general obligation bonds backed by states and municipalities, as well as revenue bonds tied to projects like hospitals, utilities, and transportation infrastructure. The fund's holdings are weighted towards revenue bonds, which make up about two-thirds of the muni market. The average duration of MUB's ~5,800 holdings is ~6.5 years, placing it in the intermediate-term category. This balance between income and interest rate sensitivity makes MUB an attractive choice for investors seeking stability and moderate returns.

The credit profile of MUB is high quality, with ~98% of its bonds rated A, AA, or AAA. The fund generally excludes below-investment-grade bonds and omits private activity bonds that could trigger the Alternative Minimum Tax. This stringent credit profile ensures a low default risk, as investment-grade municipals have historically shown near-zero default rates.

MUB offers a 30-day SEC yield of around 3.4% as of September 2025, which, when adjusted for federal tax exemption, increases to ~5.7% for investors in the top bracket. This compares favorably to corporate options like the Vanguard Intermediate-Term Corporate Bond Index Fund (VCIT). The fund charges a 0.05% expense ratio, one of the lowest in the category, and is highly tax-efficient with a portfolio turnover averaging between 10–20% annually and rare capital gains distributions.

MUB is commonly used in taxable brokerage accounts, particularly for investors in higher tax brackets, where federally tax-exempt income is a significant advantage. Over longer periods, MUB has produced the highest returns of its peers, with significantly better results for investors in moderate-to-high federal brackets. However, it is not the best match for tax-advantaged accounts like IRAs, where a taxable bond fund with a higher yield is preferred.

Institutions like banks and insurers often use MUB for liquidity, without the complexity of selecting and monitoring individual municipal bonds. Volatility, measured by standard deviation, normally hovers around 4–5%, placing MUB in the middle of the risk spectrum for fixed income.

MUB's performance across different market environments is noteworthy. In stable rate environments and soft landings, high-grade municipal bonds tend to perform well, benefiting from MUB's tax-exempt income and moderate volatility. During recessions or risk-off periods, investors often favor Treasuries, but high-quality municipal bonds have generally held up well and recovered as market conditions improve. Falling rates tend to lift bond prices, benefiting intermediate-duration funds like MUB, which avoid the reinvestment risk common to shorter-duration funds. However, MUB's price usually declines in rising-rate environments, though less severely than long-term muni funds.

MUB's peers include the Vanguard Tax-Exempt Bond ETF (VTEB), SPDR Nuveen Bloomberg Municipal Bond ETF (TFI), and VanEck Intermediate Muni ETF (ITM). These funds are also passively managed and federally tax-exempt, commonly used as core holdings in taxable portfolios. While MUB's performance has been in line with these peers, it has a slightly higher Sharpe ratio, indicating better risk-adjusted returns.

In summary, the iShares National Muni Bond ETF (MUB) is a passive, investment-grade municipal bond fund with a strong credit profile, offering federally tax-exempt income. Its low cost and intermediate duration make it a common choice for investors in higher tax brackets seeking tax-efficient income with moderate risk. MUB's performance and risk profile position it as a solid option for investors looking to diversify their fixed income portfolios.