10-Year Treasury Yields Move Above 5% as Income Seekers Pile In. Even Tax-Exempt Municipal Bond Interest Can Increase Social Security Taxes

Municipal bond interest is federally tax-free, but for retirees who receive Social Security, it can still unexpectedly create a tax bill that a taxable CD would not. The IRS formula behind that result can surprise even experienced savers.

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Imagine a retiree who gets $30,000 a year from Social Security and another $10,000 from an IRA. With bond yields rising, he decides to shift some savings into municipal bonds so he can collect interest the IRS will not tax.

The idea seems timely. In commentary published in late October 2026, Cooper Howard of the asset management arm of Charles Schwab (NYSE:SCHW | SCHW Price Prediction) said the 10-year Treasury yield had recently moved above 5%. He also noted that municipal bonds could look attractive to investors in higher tax brackets. At the same time, FDIC data showed the national average 12-month CD rate at 1.76% as of Oct. 19.

But retirees who collect Social Security face an important catch. Even though municipal bond interest is generally exempt from federal income tax, the IRS still includes it when determining how much of a person’s benefits are taxable. That can make the investment less rewarding than it first appears.

Tax-Free Interest Still Counts in the Social Security Formula

The IRS uses a measure called combined income to figure out how much Social Security is taxable. It includes adjusted gross income, tax-exempt interest and half of annual benefits. In other words, municipal bond interest is counted in the calculation even though the interest itself is generally exempt from federal income tax.

That total is then measured against a base amount of $25,000 for single filers or $32,000 for married couples filing jointly.

For retirees considering Howard’s muni-bond scenario, once combined income goes above $34,000 for individuals or $44,000 for joint filers, as much as 85% of benefits can become taxable.

Take Frank, a hypothetical retiree. Before he buys municipal bonds, half of his benefits plus his other income adds up to $25,000. That puts him right at the threshold for single filers, so none of his Social Security is taxable.

Then he purchases municipal bonds that pay $12,000 a year in tax-exempt interest. His combined income rises to $37,000, putting him above both thresholds. The bond interest remains federally tax-free, but $7,050 of his Social Security benefits now becomes taxable. He has not received any additional Social Security income, yet he may owe more federal income tax.

Between the two thresholds, each additional dollar of income can cause up to half a dollar of benefits to become taxable. Once income moves above the upper threshold, where Howard’s higher-bracket investors often fall, that share can rise to 85% of each extra dollar until the overall cap applies. Frank’s exact taxable amount would require the full IRS worksheet, but the municipal bond interest clearly pushes more of his benefits into taxable income.

It is important to separate the share from the tax rate. Even for the investors Howard was discussing, the 85% figure is only the maximum portion of benefits that counts as taxable income. That portion is then taxed at the ordinary rate, much like IRA withdrawals.

Why Middle-Income Retirees Can Be Blindsided

Municipal bond yields are often compared with taxable investments using taxable-equivalent yield, which estimates what a taxable bond would need to pay to match a muni’s after-tax return. But that comparison can miss the effect on Social Security. For someone like Frank, tax-free interest can still increase the amount of benefits subject to federal income tax.

Higher-income retirees may be less surprised. Once 85% of their Social Security is already taxable, additional municipal bond interest will not increase that share. But crossing the $34,000 threshold does not automatically mean reaching the maximum. The extra tax burden can be especially noticeable for retirees whose benefits are still moving into taxable territory.

This middle group is growing over time. The threshold amounts are fixed dollar figures in the law and are not adjusted for inflation. Benefits, meanwhile, rise with each cost-of-living increase. A 3.6% increase for 2027 would lift the average retired worker’s monthly check to about $2,170, pushing more people closer to the line.

This gradual threshold creep is one of several IRS rules that can quietly reduce retirement income without drawing much attention. It was included alongside eight others in a free tax trap guide for retirees.

Do the After-Tax Math Before Chasing Yield

Before buying municipal bonds, run two versions of your tax return through software or the IRS worksheet: one with the municipal-bond interest and one with a taxable alternative such as Treasuries or CDs. Then compare the total tax bill under each version. Pay close attention to how much of your Social Security becomes taxable, because that number can change more than expected.

The most difficult mistake to undo is locking a large share of savings into long-term bonds based on a yield that ignores this interaction. Selling bonds early can also mean taking a loss if rates rise.

Filing status, state taxes and other sources of income can all change the outcome, so it is worth testing your own numbers. For a retiree like Frank, the best yield is the one that leaves the most money after taxes. Sometimes that ends up being the bond with the less exciting label.