The pitch for the iShares National Muni Bond ETF (NYSEARCA:MUB) is almost aggressively boring, and that is the point. While every brokerage feed screams about AI capex and $4 trillion market caps, MUB quietly sits on $45.7 billion in assets and does one thing.
It pays federally tax-exempt interest from a giant, diversified pool of U.S. municipal bonds. For a taxable-account investor in a high bracket, MUB is the plumbing you install once and stop thinking about. Which is exactly why it deserves a hard look rather than a fact-sheet skim.
What MUB Holds
MUB tracks an index of investment-grade U.S. munis and, per BlackRock, spreads its money across 6,721 bonds. That kind of breadth is why a single defaulting hospital authority or struggling school district barely nudges the NAV. The expense ratio is 0.05%, which for a fund of this size and complexity is close to free.
The return engine is straightforward. Coupon interest from state and local government bonds flows through to shareholders monthly, and because that interest is federally tax-exempt, the headline yield understates what a high-bracket investor actually keeps. The current 30-day SEC yield sits at 3.35%, and the tax-equivalent SEC yield is 5.66%. That gap is the whole game.
The Tax-Free Income Case, Made Concrete
Consider a married couple pulling income into the 37% top federal bracket, which kicks in above $768,700 for 2026. A 3.35% tax-free coupon lands in their pocket at full strength. A taxable bond would need to yield roughly 5.66% pre-tax to match, and the current 10-year Treasury pays 4.49%. Treasuries lose that comparison for this investor, and it is not close.
Muni supply is part of why yields still look this good. Lord Abbett has argued that municipal yields remain near the highest levels of the past decade, with a steep muni curve. Franklin Templeton notes that new tax-exempt issuance is running more than 9% above 2025’s record pace, though fund flows have absorbed it. Schwab’s midyear view is more measured, warning that elevated supply, rate uncertainty, and issuer dispersion are real risks alongside the tax-efficient income story.
Why MUB Is Not a Cash Substitute
This is where holders get in trouble. MUB carries an effective duration of 6.19 years, meaning a 100 basis point jump in yields would drag the price down roughly six points. Compare that to the 1.65% national average 12-month CD, which is boring in a different way. The CD cannot lose principal. MUB can, and did, during 2022.
The recent tape underscores the point. MUB is up 1.7% year-to-date and 6.2% over the past year, but the five-year total price return is only 4.55%. Rates matter. With the 10-year yield sitting in the 93rd percentile of its trailing-year range and the Fed funds rate held at 3.75% for seven months, the entry point today looks better than it did a year ago, but there is no free lunch on the duration.
Where MUB Fits in Your Portfolio
MUB belongs in the income and ballast sleeve of a taxable account for an investor in the 32% bracket or higher, ideally as a 10% to 25% allocation next to equities and shorter-dated cash equivalents.
It is a poor fit inside an IRA or 401(k), where the tax exemption is wasted, and a genuinely bad fit for anyone treating it as a savings account. If you need the money in 18 months, use T-bills. If you want tax-efficient, diversified, intermediate-term income and can stomach the occasional 5% drawdown when rates spike, MUB is one of the cleanest ways to buy that exposure at five basis points a year.
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