iShares National Muni Bond ETF (MUB)

The iShares National Muni Bond ETF (MUB) holds a diversified portfolio of municipal bonds — debt issued by US states, cities, and local agencies to fund infrastructure, schools, hospitals, and other public needs. When you own MUB, you own a piece of hundreds of these bonds and collect interest payments that are free from federal income tax, a feature that makes municipal bonds attractive to investors in higher tax brackets.

What a municipal bond actually is

A municipal bond is a loan you make to a state or city. You give them money today, they pay you interest for a set number of years, and you get your principal back at the end. The catch is simple: the interest you earn is not taxed by the federal government. Many municipal bonds also escape state and local tax if you buy a bond issued in your home state. This tax advantage exists because Congress wanted to make it cheaper for states and cities to borrow money for public projects — a policy that has been in place since 1913.

MUB does the picking for you. Instead of having to research individual bonds and figure out which cities are financially stable, you buy shares in the fund and own a slice of hundreds of bonds across different states, cities, and sectors. This diversification means your return is not riding on whether one city hits a pothole in its finances.

How MUB is built

The fund tracks an index of investment-grade municipal bonds — that means bonds rated as low-risk by credit agencies like Moody’s or Standard & Poor’s. The portfolio holds bonds across the full maturity spectrum, from bonds due in a few years to bonds that will not mature for 30 years. It includes general obligation bonds (backed by a city’s full taxing power) and revenue bonds (backed by the income from specific projects, like toll roads or water systems). The fund holds roughly 2,000 different bonds at any time, so you are very diversified: a problem with one municipality is a tiny dent in your returns.

The fund rebalances regularly to match the makeup of its underlying index. It buys and sells as new bonds are issued and old ones mature. This is mostly invisible to shareholders, but it does mean the fund naturally has some turnover and some capital gains or losses as bonds are traded. Those gains pass through to shareholders, though they remain tax-free at the federal level (assuming you are a federal taxpayer holding the fund in a regular account).

The expense ratio — how much the fund charges you annually to own it — is very low, in the range of 0.05 percent. You pay roughly $5 per year to own $10,000 worth of the fund. That is cheap because MUB is mechanically managed: it is just tracking an index, not paying analysts to pick bonds.

Why you earn less than other bonds

A key thing to understand: municipal bonds pay lower interest than comparable corporate or Treasury bonds. A corporate bond and a municipal bond with identical default risk will nearly always pay less interest if it is a muni — sometimes a lot less. Why? Because the tax break is valuable. An investor in the 37 percent federal tax bracket will effectively get 37 percent more money from a municipal bond, after taxes, than from a taxable bond paying the same rate. So issuers can offer less and still attract buyers.

This means MUB makes sense only if you are paying federal income tax at a high enough rate that the tax savings beat the lower yield. If you are in a low tax bracket, a plain bond fund or Treasury fund will probably give you more money in your pocket after taxes. A rough rule of thumb: munis start to make sense in the 24 percent federal bracket or higher, though it depends on state taxes too.

The risks and where the value lives

Municipal bonds are generally safe — cities rarely default, and when they do it is usually unexpected. But they do carry interest-rate risk: if federal interest rates rise sharply, the market value of existing bonds falls, and if you need to sell before maturity you will sell at a loss. MUB is not a bond ladder (where you hold each bond to maturity) — it is a fund that trades, so its price fluctuates daily based on interest rates and the perceived health of issuers.

Credit risk exists, too. In rare cases, a city or state can get into real financial trouble. Detroit’s bankruptcy in 2013 and Puerto Rico’s debt crisis in 2017 both roiled the municipal bond market. MUB holds investment-grade bonds, which means higher-quality borrowers, but it is not risk-free.

The real value in MUB for a high-income earner is this: you get a diversified portfolio of bonds that will likely mature without incident, you pay almost nothing to own it, and you do not pay federal tax on the interest. If a major corporation offered you a bond paying 4 percent and Uncle Sam would let you keep it tax-free, that is a very good deal. That is what MUB offers, scaled across hundreds of municipalities.

How to use it and what to know

MUB works best as a core fixed-income holding for people in higher tax brackets. It is not a place to park money you need in a year — bond prices move with interest rates, and you could sell at a loss. It is better suited to someone with a five-year or longer horizon who wants steady income that avoids federal tax.

Before buying, check your tax bracket and calculate the equivalent taxable yield — the yield you would need from a taxable bond to net the same money after taxes. Compare that to what corporate bonds and Treasuries are paying. If munis are significantly cheaper to own, they make sense; if not, you might be better off in a regular bond fund.

The prospectus and fact sheet on the iShares website list the current yield (annual interest as a percentage of price), the average maturity of holdings, and the breakdown by state and sector. Monitor your state’s credit health if you hold a large position — major downgrades can affect prices. And remember: municipal bonds are tax-free federally, but not always state-free if you hold bonds from another state. Buy bonds from your home state if you can, or account for state tax when comparing yields.