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If you own the iShares National Muni Bond ETF (NYSEARCA:MUB), you likely bought it for one reason: federally tax-exempt income at a rock-bottom price. MUB is the largest broad national muni ETF, charges a 0.05% expense ratio, and has thrown off $3.413726 per share in trailing distributions on a $105.68 share price. For a high-bracket investor in a taxable account, that math is legitimately attractive, and there is nothing wrong with wanting to own MUB.
The problem is what happens after that interest hits your Form 1040. Muni income does two unhelpful things at once: it is invisible to the tax break most retirees hope will offset their bond income, and it is fully counted against the one tax formula that determines how much of your Social Security check the IRS keeps.
Two Tax Traps Hiding Inside Line 2a
Tax-exempt interest lands on line 2a of the 1040. Under Internal Revenue Code Section 103, that interest is not includable in gross income for federal income tax purposes. Sounds clean. It isn’t.
First, the SALT problem. The state and local tax deduction is a deduction against income taxes you paid. Muni interest is income you did not pay federal tax on in the first place, so it produces no SALT deduction, no state-income-tax offset, and no interaction with the SALT cap. If part of your MUB thesis was that tax-free income would somehow ease your SALT burden, it does not. The two live in separate parts of the tax code.
Second, and more damaging, the Social Security provisional-income formula explicitly adds tax-exempt interest back in. Provisional income equals adjusted gross income plus one-half of your Social Security benefits plus your muni interest. Cross $25,000 single or $32,000 joint, and up to 50% of benefits become taxable; cross $34,000 or $44,000, and up to 85% do. MUB’s monthly checks quietly push you across those lines while pretending to be invisible (it is one of several IRS rules that quietly siphon money out of retirement accounts, and we charted the rest in a free guide here: The Retiree’s Tax Trap Map).
Where That Leaves the Incumbent
MUB is still doing its job. It delivered a 4.82% total return over the past year and a 19.35% ten-year return, with monthly federally exempt income. The fund is fine. The question is whether the wrapper still fits your tax picture, particularly if you are drawing Social Security or plan to within a few years.
A Cleaner Muni Swap: VTEB
If you want to keep passive, investment-grade national muni exposure, the direct swap is Vanguard Tax-Exempt Bond ETF (NYSEARCA:VTEB). VTEB tracks a comparable national investment-grade muni index and has produced a slightly better 5.07% one-year return and 20.5% ten-year return versus MUB’s numbers above. Its trailing 12-month distributions came to $1.6981 per share on a $49.66 price.
VTEB does not fix the Social Security trap. It is still muni interest, still line 2a, still added back into provisional income. What it does is deliver essentially the same exposure with a small, persistent structural edge that has shown up in trailing returns. If you have already decided the muni wrapper is right for your bracket, VTEB is the lower-friction way to own it.
When the Right Swap Is Out of Munis Entirely
For retirees pinned near the provisional-income thresholds, the better move may lie outside munis altogether. With the 10-year Treasury at 4.71%, a taxable Treasury paying interest that is exempt from state tax but taxed federally can beat a muni after you account for the Social Security phantom tax. Muni interest still counts in provisional income; a Roth IRA distribution does not. Shifting bond exposure into a Roth, or trading part of a MUB position for Treasuries held in a taxable account, can lower the tax that MUB is quietly creating on your benefits.
Leveraged closed-end muni funds such as Nuveen Municipal Credit Income Fund (NYSE:NZF) and PIMCO Municipal Income Fund II (NYSE:PML ) pay more but make the Social Security problem worse, not better, because higher tax-exempt interest means a bigger provisional-income add-back. PML’s five-year price return of -34.35% is a reminder that leverage cuts both ways.
How to Decide Before Year End
Pull your last 1040. Add your AGI, half your Social Security, and the line 2a number. If you are comfortably below $32,000 joint or well above $44,000, MUB or VTEB continues to make sense and the swap decision is really about fees and tracking. If you are sitting inside those bands, the tax-exempt label is doing less for you than the ticker implies, and the practical fix is to move part of the position into a Roth or into Treasuries, not to chase yield in a leveraged muni CEF.
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