Not Always Tax-Free: 7 Municipal Bond Tax Traps

April 6, 2021 Cooper Howard
If you're interested in tax-free municipal bonds, you might want to keep an eye out for these seven tax traps.

Investors often think of municipal bonds, which are sold by local and state governments to fund public projects like building new schools and repairing city sewer systems, as being totally tax-free—but that's not always the case.

While the interest payments on munis are usually exempt from federal income taxes, other taxes may apply. It's important to know the rules, because municipal bonds are one of the few investments available to income-oriented investors looking to reduce their income tax bills. Here are seven types of taxes that could apply if you buy muni bonds.

1. De minimis tax. The de minimis tax applies to munis that you acquired at a market discount. The de minimis rule says that for bonds purchased at a discount of more than 0.25% for each full year from the time of purchase to maturity, gains resulting from the discount are taxed as ordinary income rather than capital gains. The ordinary income tax rate is generally greater than the capital gains rate, which could result in a greater bite out of your yield.

The NutFor example, take a bond that matures in 10 years with a face value of 100. The de minimis "breakpoint" on this bond is 97.5 (100 – [0.25 × 10 years]). If you bought this bond for less than 97.5, you would be required to pay ordinary income tax on the discount.

De minimis thresholds for a $10,000 face value muni

De minimis thresholds for a $10,000 face value muni
Years to maturity Acquisition threshold Years to maturity Acquisition threshold Years to maturity Acquisition threshold
1 $9,975 11 $9,725 21 $9,475
2 $9,950 12 $9,700 22 $9,450
3 $9,925 13 $9,675 23 $9,425
4 $9,900 14 $9,650 24 $9,400
5 $9,875 15 $9,625 25 $9,375
6 $9,850 16 $9,600 26 $9,350
7 $9,825 17 $9,575 27 $9,325
8 $9,800 18 $9,550 28 $9,300
9 $9,775 19 $9,525 29 $9,275
10 $9,750 20 $9,500 30 $9,250

What you can do: To avoid the de minimis tax rule, consider purchasing bonds priced at par or at a premium to their face value. Paying a premium may mean having to make adjustments to your tax filing, but the associated tax benefits more than offset the added complication, in our view. In addition, if a bond is selling at a premium, it's likely because it is offering a high coupon rate.

2. Alternative minimum tax. There are two parallel income tax systems in the United States: ordinary income tax and alternative minimum tax (AMT), which disallows a number of deductions that are allowed in the ordinary income tax code. Taxpayers must calculate their tax under each system, then pay whichever is higher—ordinary or AMT.

Income from some municipal bonds—for example, those that fund stadiums, airports or more businesslike enterprises—might be subject to AMT. If you have to pay AMT and hold such a bond, your interest income would generally be taxed at the applicable AMT rate—which could be 26% or more, if you're in the AMT exemption phase-out range. Effectively, that means the yield on a municipal bond paying 2.00% would drop to 1.48%. The 2017 tax law increased the phase-out thresholds for AMT meaning fewer filers will be subject to AMT under the new tax laws. The phase-out threshold is $1,047,200 for 2021 for married filing jointly.

What you can do: For bonds held at Schwab, you can find out if a municipal bond is subject to AMT by accessing the "Research" page after logging into, searching for a municipal bond and viewing its "Security Description" page. You can also contact a Schwab Fixed Income Specialist at 877-566-7982.

3. Increase in taxation of Social Security benefits. Although municipal bonds generally aren't subject to federal taxes, the IRS does include income from such bonds in your modified adjusted gross income (MAGI) when determining how much of your Social Security benefit is taxable. If half of your Social Security benefit plus other income, including tax-exempt municipal bond interest, amounts to more than $44,000 for a joint return ($34,000 for individual), up to 85% of your Social Security benefits may be taxable.

What you can do: If you are receiving Social Security benefits, we suggest reviewing IRS Publication 915, "Social Security and Equivalent Railroad Retirement Benefits," or this page from the Social Security Administration, which both discuss the taxation of retirement benefits, to determine how this might apply to your individual situation.

4. Increase in Medicare premiums. If you're covered by Medicare, the federally tax-exempt interest from municipal bonds may increase the amount you pay for Medicare Part B or Medicare prescription drug coverage. If you're married and filing jointly and your MAGI is more than $170,000 ($85,000 for single filers), you will be required to pay an additional amount for Medicare Part B and Medicare prescription drug coverage.

Income to determine monthly Medicare premiums may include municipal bond interest

Income to determine monthly Medicare premiums may include municipal bond interest
Modified adjusted
gross income (MAGI) - individuals
Modified adjusted
gross income (MAGI) - married couples
Part B monthly
premium amount
Prescription drug company monthly premium amount
Less than $88,000 Less than $176,000 2021 standard premium = $148.50 Your plan premium
$88,000 up to $111,000 $176,000 up to $222,000 Standard premium + $59.40 Your plan premium + $12.30
$111,000 up to $138,000 $222,000 up to $276,000 Standard premium + $148.50 Your plan premium + $31.80
$138,000 up to $165,000 $276,000 up to $330,000 Standard premium + $237.60 Your plan premium + $51.20
$165,000 up to $500,000 $330,000 up to $750,000 Standard premium + $326.70 Your plan premium + $70.70
Equal to or above $500,000 Equal to or above $750,000 Standard premium + $356.40 Your plan premium + $77.10

To determine your Medicare premiums, the Social Security Administration generally uses your most recent federal tax return. For example, to determine 2021 monthly adjustment amounts, the Social Security Administration would use your tax return for tax year 2019. You can learn more about Medicare premiums in the Social Security Administration publication "Medicare Premiums: Rules For Higher-Income Beneficiaries."

What you can do: We don't believe paying an additional Medicare premium justifies not investing in municipal bonds. Given that your MAGI will also include income from other sources, such as dividend income and interest income from taxable bonds, avoiding municipal bonds will not necessarily allow you to avoid the increase in Medicare premiums. Also, investing in zero-coupon bonds likely won't allow you to avoid paying higher premiums, because the part of the increase in the zero-coupon bonds' value may be included in the calculation to determine your Medicare premiums.

5. Capital gains tax. We generally suggest individual investors hold a bond until maturity. However, if you need to sell earlier and you receive a price greater than your cost basis—your acquisition price after adjusting for any premiums paid or discounts received—the gain will be subject to capital gains tax.

What you can do: Determining cost basis for an individual bond can get complicated, as there are special reporting rules that govern the adjustments to a bond's acquisition price. For bonds held at Schwab, you can find your adjusted cost basis on the "Positions" page after you log into

6. State income tax. If you purchase a bond from your home state, generally the interest payments you receive will be exempt from state income taxes. However, interest paid on bonds from outside of your home state typically will be subject to state income tax. Interest payments on some in-state munis may also be subject to state income taxes.

What you can do: If you live in a state with low tax rates or one that issues a minimal amount of municipal bonds, we would suggest looking outside your home state. The added benefits of diversification and potentially higher yields might make up for the hit you would take by paying state income taxes.

7. Taxable municipal bonds. Some munis are taxable. For example, roughly 30% of the munis issued in 2020 were taxable. Issuance of taxable munis has increased recently as a result of the 2017 tax law changes and low absolute yields. Taxable muni bonds generally yield more than tax-free bonds to make up for the difference.

What you can do: For investors in lower tax brackets and investing in taxable accounts, or those investing in either Roth or traditional IRA accounts, we believe taxable municipal bonds can make sense compared to other taxable bonds because, historically, munis have exhibited stronger credit characteristics than corporate bonds of comparable ratings.

The bottom line is that municipal bonds offer significant tax advantages and could make sense in the portfolios of many income-focused investors. However, the details matter. If you are highly tax-sensitive and would like to invest in these securities, you will want to make sure you understand how the tax traps mentioned above might affect your portfolio.

If you have questions about your portfolio, you could consult IRS Publication 550, "Investment Income and Expenses," or check in with your tax advisor.

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