Interest on most state and local government bonds is exempt from federal income tax under Section 103 of the Internal Revenue Code, and this is what people mean when they talk about the tax-free municipal bond interest exemption. The exclusion is real, but it is narrower than the phrase “tax-free” suggests. Municipal bond interest can still trigger the alternative minimum tax, increase how much of your Social Security benefits are taxed, push up your Medicare premiums, and be fully taxable on your state return. Understanding where the exemption stops matters as much as knowing it exists.
What Section 103 Actually Excludes
Gross income does not include interest on any state or local bond that meets the requirements set out in the tax code.1Office of the Law Revision Counsel. 26 USC 103 – Interest on State and Local Bonds A qualifying bond is one issued by a state, the District of Columbia, a U.S. territory, or a political subdivision such as a city, county, school district, or transit authority.
This is an exclusion, not a deduction. The interest never enters your gross income at all, so it does not sit inside your tax bracket calculation or push other income into a higher rate. That structural point drives the appeal. For a taxpayer in the 37% federal bracket, a 4% tax-exempt yield is worth roughly 6.35% on a taxable bond, which is why higher-income investors gravitate to municipals.
Three categories of bonds are carved out of the exemption. Private activity bonds that do not qualify as “qualified bonds” under Section 141 lose it.2Office of the Law Revision Counsel. 26 USC 141 – Private Activity Bond; Qualified Bond Arbitrage bonds, where the issuer reinvests proceeds into higher-yielding investments, are disqualified under Section 148.3Office of the Law Revision Counsel. 26 USC 148 – Arbitrage Bonds that fail the procedural and information-reporting rules of Section 149 are also disqualified. You do not need to evaluate any of this yourself as a bondholder. The offering documents state whether interest is federally tax-exempt, and your brokerage will label the security accordingly.
Which Bonds Qualify
Municipal bonds come in two broad forms, and both can carry tax-exempt interest.
General obligation bonds are backed by the full faith and credit of the issuing government, meaning the issuer pledges its taxing power to repay. They typically fund schools, roads, and civic buildings, and because repayment draws on broad tax revenue, they generally carry lower credit risk.
Revenue bonds are repaid from income generated by a specific project, such as highway tolls, water utility fees, or hospital revenue. They often pay slightly more to compensate for the narrower repayment source. If the project underperforms, bondholders bear more risk than they would with a general obligation bond.
Both types get the Section 103 exemption if they meet the statutory requirements. Original issue discount on a tax-exempt bond is itself treated as tax-exempt interest, so you do not owe federal tax on the accretion of a bond you bought at a discount at original issuance.4Internal Revenue Service. Tax-Exempt Interest
The Private Activity Bond Exception
Not every bond issued by a government body counts as a governmental bond. When more than 10% of proceeds fund a private business use, the bond is classified as a private activity bond under Section 141 (the threshold drops to 5% for unrelated or disproportionate private use). Stadiums with naming-rights deals, privately managed convention centers, and airport terminals leased to airlines are common examples.
Some private activity bonds still qualify for tax-exempt interest as “qualified bonds,” including bonds for affordable housing, student loans, certain nonprofit hospitals, and qualified transportation facilities. If a private activity bond does not meet those criteria, its interest is fully taxable federally.
The AMT Trap on Private Activity Bonds
Even when a private activity bond is a qualified bond with tax-exempt interest under Section 103, that interest is treated as a tax preference item for the alternative minimum tax.5MSRB. Tax Treatment If you are subject to the AMT, this “tax-free” interest gets added back into your income for AMT purposes and can generate a bill you did not expect.
For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married couples filing jointly, with phase-outs beginning at $500,000 and $1,000,000 respectively. Official statements and brokerage security descriptions disclose whether a bond is AMT-subject. If your income is anywhere near the phase-out range, check the label before you buy.
Capital Gains and the De Minimis Rule
The Section 103 exclusion covers interest and nothing else. Sell a municipal bond on the secondary market for more than you paid and the profit is a capital gain, taxed federally like any other investment gain. For 2026, long-term rates run 0%, 15%, or 20% depending on taxable income.
Bonds bought at a discount on the secondary market bring an extra complication. The de minimis threshold is 0.25% of face value for each full year until maturity. Discounts below the threshold are taxed at capital gains rates when the bond matures or is sold. Discounts above the threshold produce ordinary income on the discount portion, which is a materially worse outcome for most investors.
Take a bond maturing in 10 years. The de minimis threshold is 2.5% of face value, or $25 on a $1,000 par bond. Buy it for $980 and your $20 discount stays under the threshold, so the gain at maturity is a capital gain. Buy it for $970 and the $30 discount exceeds the threshold, converting the discount-related gain into ordinary income. This is the sort of detail that can quietly erode the tax advantage of a “tax-free” bond.
What This Costs Retirees Through Social Security and Medicare
Tax-exempt interest stays out of your adjusted gross income but appears in two other calculations that catch retirees off guard.
Social Security Benefit Taxation
The IRS uses “combined income” to decide how much of your Social Security is taxable. That figure equals your adjusted gross income, plus half your Social Security benefits, plus your tax-exempt interest. Cross $25,000 as an individual filer or $32,000 as a joint filer and up to 50% of benefits become taxable. Cross $34,000 or $44,000 and up to 85% is taxable. Municipal bond interest pushes you toward those thresholds even though the interest itself is not taxed.
Medicare Premium Surcharges
Medicare Part B premiums rise for higher-income beneficiaries through the Income-Related Monthly Adjustment Amount. The Social Security Administration calculates IRMAA using modified adjusted gross income, which explicitly includes tax-exempt interest. For 2026, individual filers with MAGI above $109,000 (or joint filers above $218,000) pay a surcharge running from $81.20 to $487.00 per month on top of the standard Part B premium.6CMS. 2026 Medicare Parts A and B Premiums and Deductibles A large muni portfolio generating substantial tax-exempt interest can bump you into a higher IRMAA bracket, adding thousands in annual Medicare costs that offset some of the tax savings.
State Tax Treatment
Federal tax exemption does not carry over to your state return automatically. Most states exempt interest on bonds issued within their own borders but tax interest from out-of-state municipal bonds at ordinary state income rates. If you live in a high-tax state and hold a nationally diversified muni bond fund, a real slice of that “tax-free” income may be taxable on your state return. A few states with no income tax make this a non-issue, and a few others exempt all municipal bond interest regardless of origin. Check your state’s rule before assuming anything.
How to Report Tax-Exempt Interest
You still have to report the interest even though it is excluded from federal tax. All taxable and tax-exempt interest must appear on your federal return, and reporting it is an information requirement that does not convert it into taxable income.7Internal Revenue Service. Topic No. 403, Interest Received
Your broker or the issuer sends a Form 1099-INT with tax-exempt interest in Box 8. AMT-subject private activity bond interest appears separately in Box 9. The Box 8 total goes on line 2a of Form 1040. If you own a mutual fund or ETF that holds municipal bonds, the fund reports exempt-interest dividends in Box 12 of Form 1099-DIV, and that amount also goes on line 2a.8Internal Revenue Service. 1040 (2025) Instructions
One detail trips people up. If you bought a tax-exempt bond at a premium, report only the net interest on line 2a: interest received minus the amortized bond premium for the year.9Internal Revenue Service. Instructions for Schedule B (Form 1040) Skip that adjustment and you overstate your exempt interest, which then inflates the MAGI figure used for IRMAA and Social Security taxation.