Tax-exempt bonds are debt securities, most of them issued by state and local governments, whose interest income is excluded from federal income tax under Internal Revenue Code Section 103.1Office of the Law Revision Counsel. 26 USC 103 – Interest on State and Local Bonds They’re commonly called municipal bonds, or “munis,” and they’re one of the few ways to collect investment income without an immediate federal tax hit. The treatment is narrower than “no taxes ever,” though. Capital gains when you sell are fully taxable, certain bonds trigger the Alternative Minimum Tax, and the interest can still raise a retiree’s Medicare premiums and the taxable portion of Social Security benefits.
How the Exemption Works
When you buy a muni, you’re lending money to a government entity in exchange for regular interest payments and the return of your principal at maturity. Most pay a fixed coupon rate twice a year, with maturities running from one to 30 years.2Municipal Securities Rulemaking Board. Municipal Bond Basics The borrowed funds pay for schools, highways, water systems, and similar public infrastructure.
Under Section 103, the interest you receive is simply left out of your gross income on the federal return. It isn’t added in and then subtracted; it never enters the calculation. That exclusion is effectively a subsidy. Because buyers don’t owe federal tax on the coupons, issuers can offer lower rates and still attract investors, which lowers borrowing costs for the public projects the bonds finance.
Comparing Muni Yields to Taxable Bonds
A 4% muni and a 4% corporate bond are not the same investment after taxes. To compare them fairly, divide the muni’s yield by one minus your marginal federal tax rate. The result is the tax-equivalent yield: the pretax return a taxable bond would need to match the muni’s after-tax income.
Take a 24% federal bracket investor looking at a muni yielding 3.5%. The math is 3.5% ÷ (1 − 0.24) = 4.61%. A taxable bond would have to pay at least 4.61% to come out even. For someone in the 37% bracket, that same 3.5% muni carries a tax-equivalent yield of roughly 5.56%. The higher your rate, the more the exemption is worth, which is why munis are most popular with investors in the top brackets.
If your state also exempts the interest, you can run the calculation with your combined federal and state marginal rate, which pushes the tax-equivalent yield higher still. In high-tax states, that often makes munis attractive at coupon rates that look mediocre on paper.
State and Local Tax Treatment
The federal exemption is only part of the picture. Whether you also skip state and local income tax depends on where you live and who issued the bond. Many states exempt interest on bonds issued inside their borders. If your city does the same for locally issued bonds, you get “triple tax-exempt” income, free of federal, state, and local tax. Buy a bond from another state and your home state will usually tax that interest like any other investment income.
Bonds issued by U.S. territories get special treatment. Interest on Puerto Rico government bonds is exempt from state and local taxes regardless of where the bondholder lives.3Office of the Law Revision Counsel. 48 USC 745 – Tax Exempt Bonds Guam, the U.S. Virgin Islands, and American Samoa have similar provisions, which makes territory bonds effectively triple tax-exempt for investors in every state.
What’s Still Taxable
The exemption covers interest income only. Sell a muni for more than you paid and the profit is a taxable capital gain, no different from selling stock.4Municipal Securities Rulemaking Board. What to Expect When Selling Municipal Bonds Before Maturity For 2026, long-term capital gains rates (on bonds held longer than a year) are 0%, 15%, or 20% depending on income. Short-term gains are taxed at ordinary rates.
Market Discount Bonds
Buying a muni on the secondary market below face value introduces a wrinkle. The IRS applies a de minimis test: multiply 0.25% of face value by the number of full years to maturity. If the discount you paid is below that threshold, appreciation at sale or redemption is a capital gain. If the discount exceeds the threshold, the appreciation is taxed as ordinary income.5Municipal Securities Rulemaking Board. Tax and Liquidity Considerations for Buying Discount Bonds
A $1,000 face value bond with 10 years to maturity has a de minimis threshold of $25 (0.25% × $1,000 × 10). Pay $980 and the $20 gain qualifies for capital gains treatment. Pay $950 and the full $50 must be reported as ordinary income at maturity.
Original Issue Discount
Some munis are issued below face value from the start. With a tax-exempt original issue discount bond, you don’t include the accrued discount in income as years pass. Instead, you add the accrued OID to your cost basis, which reduces any gain or increases any loss when you sell or redeem.6Internal Revenue Service. Guide to Original Issue Discount (OID) Instruments
Wash Sales
The wash sale rule applies to municipal bonds. If you sell a muni at a loss and buy a substantially identical bond within 30 days before or after the sale, you cannot deduct the loss.7Internal Revenue Service. Publication 550 – Investment Income and Expenses Losses on munis are otherwise deductible as capital losses. Two bonds from different issuers, with different coupons, or different maturities are generally not substantially identical, which leaves some flexibility for tax-loss harvesting.
How Muni Interest Can Raise Medicare Premiums and Social Security Taxes
This is where many retirees get caught off guard. Even though muni interest never appears on your taxable income, two income-based calculations fold it back in.
Medicare Premium Surcharges
The Social Security Administration sets Medicare Part B and Part D premiums using modified adjusted gross income, which is your AGI plus tax-exempt interest from Line 2a of Form 1040.8Social Security Administration. Medicare Income-Related Monthly Adjustment Amount – Life-Changing Event For 2026, single filers with MAGI above $109,000 and joint filers above $218,000 begin paying income-related monthly adjustment amounts (IRMAA) on top of the standard premium.9SSA – POMS. Modified Adjusted Gross Income (MAGI) The 2026 standard Part B premium is $202.90 a month. At the highest IRMAA tier it climbs to $689.90, more than triple the baseline. A sizable muni portfolio can push a retiree into a higher tier.
Taxation of Social Security Benefits
Under IRC Section 86, modified income for Social Security purposes also includes tax-exempt interest. If that modified income plus half your Social Security benefits exceeds $25,000 (single) or $32,000 (joint), up to 50% of benefits become taxable. Above $34,000 (single) or $44,000 (joint), up to 85% of benefits can be taxed.10Office of the Law Revision Counsel. 26 USC 86 – Social Security and Tier 1 Railroad Retirement Benefits Those thresholds have never been indexed for inflation. An investor collecting $40,000 in muni interest may owe zero federal tax on the interest itself while triggering thousands of dollars in added tax on Social Security benefits.
Bonds That Lose or Limit the Exemption
Section 103 carves out three categories: private activity bonds that don’t meet the qualified bond rules, arbitrage bonds, and bonds that fail certain registration requirements.1Office of the Law Revision Counsel. 26 USC 103 – Interest on State and Local Bonds
Private Activity Bonds and the AMT
A private activity bond is issued by a government but finances a project that mainly benefits a private business. Under IRC Section 141, a bond is classified this way when more than 10% of the proceeds are used for private business purposes and more than 10% of debt service is secured by or derived from private business payments.11Office of the Law Revision Counsel. 26 USC 141 – Private Activity Bond; Qualified Bond Airport terminals leased to airlines, industrial parks for private tenants, and stadiums operated by professional teams are common examples.
Private activity bonds lose tax-exempt status entirely unless they fit one of seven qualified categories: exempt facility bonds, qualified mortgage bonds, qualified veterans’ mortgage bonds, qualified small issue bonds, qualified student loan bonds, qualified redevelopment bonds, and qualified 501(c)(3) bonds.11Office of the Law Revision Counsel. 26 USC 141 – Private Activity Bond; Qualified Bond Bonds in those categories keep federal tax-exempt treatment, but the interest counts as a tax preference item for the Alternative Minimum Tax.12Office of the Law Revision Counsel. 26 USC 57 – Items of Tax Preference
The AMT is a parallel calculation that adds preference items back into income and applies its own exemption and rates. For 2026, the AMT exemption is $90,100 for single filers and $140,200 for joint filers, with phase-outs starting at $500,000 and $1,000,000.13Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026 Investors with meaningful private activity bond holdings and income near those levels should run the AMT calculation.
Arbitrage Bonds
Section 103 also denies the exemption to arbitrage bonds. Under IRC Section 148, a bond is an arbitrage bond if the issuer invests the proceeds in securities yielding materially more than the bond’s own rate. Issuers who earn excess investment income on proceeds must rebate it to the Treasury, and failing to do so causes the bonds to lose tax-exempt status.14Office of the Law Revision Counsel. 26 USC 148 – Arbitrage You don’t control an issuer’s compliance, but a violation can retroactively make bonds in your portfolio taxable. If you’re buying individual munis, the offering documents and bond counsel opinions address arbitrage compliance.
Call Risk
Many municipal bonds include call provisions that let the issuer repay early, typically when rates drop. If your bond is called, you get your principal back (sometimes at a small premium), and the stream of tax-exempt interest stops. The real cost is reinvestment risk. A bond paying 5% that gets called after five years might leave you reinvesting at 3.5%, costing $150 a year in lost income on every $10,000 of principal for what would have been the remaining term.15FINRA. Callable Bonds – Be Aware That Your Issuer May Come Calling Before buying a callable muni, look at its yield-to-call rather than just yield-to-maturity. On a bond trading at a premium, the yield-to-call will often be meaningfully lower than the headline number.
Reporting on Your Return
Tax-exempt interest must be reported on your federal return even though it isn’t taxed. The total goes on Line 2a of Form 1040.16Internal Revenue Service. Instructions for Form 1040 Your broker or the paying agent will send Form 1099-INT showing the tax-exempt interest in Box 8. Interest on private activity bonds subject to AMT is broken out separately in Box 9.17Internal Revenue Service. Instructions for Forms 1099-INT and 1099-OID Tax-exempt OID is reported on Form 1099-OID, Box 11.
Reporting isn’t a formality. The IRS pulls the Line 2a figure into the calculations that determine whether your Social Security benefits are taxable and whether you owe Medicare premium surcharges.16Internal Revenue Service. Instructions for Form 1040 Skipping the line because the interest “isn’t taxable” is a common mistake that invites IRS notices. If you hold muni bond funds rather than individual bonds, the fund reports exempt-interest dividends on Form 1099-DIV in Box 12, and that amount also goes on Line 2a.