Rising Bond Yields Will Tempt Her Into “Tax-Free” Municipal Bonds. $25,000 of Interest Can Make 85% of Her Social Security Taxable

A 70-year-old widow has $500,000 in certificates of deposit (CDs) coming due. High-quality, long-term municipal-bond yields have climbed above 5%, their highest since the financial crisis.

She moves the whole amount into municipal bonds yielding about 5% and expects $25,000 a year that the IRS will never touch. The interest itself escapes federal income tax, but it can make her Social Security taxable, a cost that will not show up on a brokerage yield screen.

Under IRS rules, combined income includes adjusted gross income, tax-exempt interest and half of Social Security benefits. Municipal-bond interest counts even when the interest itself is exempt from federal income tax.

Why “Tax-Free” Interest Still Counts Against Her Benefits

Municipal-bond interest is excluded from federal taxable income but still reported on Form 1040 as tax-exempt interest. When the IRS determines whether your Social Security is taxable, it adds that interest back in.

That check uses something called provisional income: your other income, plus tax-exempt interest, plus half of your Social Security. For a single filer, benefits start becoming taxable once provisional income passes $25,000. Above $34,000, up to 85% of benefits can be taxed.

How $25,000 of Interest Pulls $17,900 Onto Her Return

Say she collects $24,000 a year in Social Security benefits plus $18,000 from a pension. Before buying bonds, her provisional income is $30,000, and about $2,500 of her benefit is taxable.

Add the municipal interest and provisional income rises to $55,000. Now she’s at the ceiling: $20,400, or 85% of her benefit, is taxable.

So interest sold as tax-free just put another $17,900 of Social Security on her return.

What a 5% Yield Can Really Pay

During the phase-in range, each extra dollar of tax-exempt interest can make as much as 85 cents of Social Security taxable. If those newly taxable benefits fall in the 22% bracket, that creates as much as 18.7 cents of indirect federal tax per dollar of interest. At a 12% rate, the maximum is 10.2 cents. The bond’s advertised yield does not reveal which result applies to her.

Once 85% of her benefit is taxable, additional interest cannot expose any more of it. It’s one of several subtle IRS rules that drain retirement accounts, which we mapped in a free tax trap guide.

The standard tax-equivalent-yield comparison uses only her tax bracket and ignores the benefits the interest drags in, so the fair test is simple: rerun her full return under each option and compare the dollars she keeps.

Other Limits on “Tax-Free”

1. State taxes: Interest from another state’s bonds can face your home state’s income tax.
2. Alternative minimum tax: Interest from some private-activity bonds can count toward this parallel tax system.
3. Capital gains: If she sells a bond for more than she paid, the profit is taxable.
4. Price and call risk: Higher yields often mean longer due dates or weaker credit. Bond prices fall if market yields rise.

Medicare counts the interest too. Tax-exempt interest is added back when setting income-based surcharges on Medicare premiums. For single filers in 2026, the standard Part B premium of $203 applies up to $109,000 of income. Her roughly $63,400 stays well under that.

Numbers to Run Before She Commits $500,000

• First, run the expected interest through the worksheet in Publication 915 to see whether it puts her into the 50% or 85% range and what the bond really yields after the extra tax on her benefits. Her benefits are on track for a 3% inflation adjustment for 2027. The dollar thresholds don’t adjust for inflation, so she has less room each year.
• Second, decide how much to commit. A smaller purchase reduces the tax-exempt interest entering the calculation. A bond ladder will not erase that income, but it can spread maturity dates and keep her from locking the entire $500,000 into the market at one rate.

Municipal bonds may still give her the best income for the risk she’s willing to take. She just needs to judge the yield after the tax-free interest has worked its way through the rest of her return. If you collect Social Security, run that calculation before assuming a municipal bond’s advertised yield is entirely yours to keep.

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