Interest on municipal bonds is exempt from federal income tax under 26 U.S.C. § 103, and in many cases from state and local income tax as well.1Office of the Law Revision Counsel. 26 USC 103 – Interest on State and Local Bonds That exemption is why a municipal bond paying 3.5% can beat a corporate bond paying 5% after taxes. But the exemption has edges. Some bonds still trigger the Alternative Minimum Tax, the interest counts toward the income thresholds that decide whether Social Security benefits get taxed, and any profit from selling a bond before maturity is fully taxable.
What the Federal Exemption Actually Covers
Under federal law, interest on bonds issued by states, the District of Columbia, U.S. territories, and local governments is excluded from your gross income.1Office of the Law Revision Counsel. 26 USC 103 – Interest on State and Local Bonds You owe no federal income tax on it. The exemption applies to general obligation bonds backed by a government’s taxing authority, to revenue bonds funded by tolls or utility charges, and to most other bonds issued for public purposes.
The exemption also reaches the 3.8% Net Investment Income Tax. That surtax hits ordinary interest, dividends, and capital gains once income crosses certain thresholds, but tax-exempt municipal bond interest is carved out entirely. For a high-bracket investor, escaping both the regular income tax and the NIIT makes the effective savings larger than the headline rate suggests.
Three categories of bonds lose the exemption. Private activity bonds that do not qualify under specific congressional categories are taxable. Arbitrage bonds, where the issuer reinvests the proceeds at a higher yield than the bond pays, also lose their exempt status. Bonds that are not issued in registered form do not qualify either.1Office of the Law Revision Counsel. 26 USC 103 – Interest on State and Local Bonds For most individuals buying through a broker, bonds are registered and non-arbitrage, so the private activity question is the one that comes up in practice.
State and Local Tax Treatment
The federal rule is only part of the picture. Most states that levy an income tax also exempt interest on bonds issued within their own borders. When you live in the same state that issued the bond, you typically pay zero federal, state, and local tax on the interest. Investors in high-tax states like New York and California actively seek in-state bonds for this reason, and issuers there can offer lower coupon rates because the after-tax value still competes.
Buy a bond from a different state and the math changes. The federal exemption still applies, but your home state will generally tax that interest as ordinary income. State income tax rates run from zero to above 13%, so the drag varies widely. A diversified national municipal bond fund will distribute some out-of-state interest that is taxable on your state return even though it stays federally exempt.
Bonds From U.S. Territories
Bonds issued by Puerto Rico, Guam, the U.S. Virgin Islands, American Samoa, and the Northern Mariana Islands sit in their own category. The federal tax code defines “State” to include any U.S. possession, so interest on those bonds qualifies for the federal exclusion under the same statute that covers state and local bonds.1Office of the Law Revision Counsel. 26 USC 103 – Interest on State and Local Bonds Most states also exempt territory bond interest from state income tax regardless of where the investor lives, producing what is often called a triple tax exemption. The tradeoff is credit risk. Yields on some territory bonds, particularly from Puerto Rico, have historically run higher than comparably rated state bonds for that reason.
Private Activity Bonds and the AMT
A private activity bond is one where more than 10% of the proceeds fund private business use and more than 10% of the debt service is tied to that private use.2Office of the Law Revision Counsel. 26 USC 141 – Private Activity Bond; Qualified Bond Common examples include bonds financing a privately operated airport terminal or a stadium leased to a professional team. Congress has approved several categories of “qualified” private activity bonds whose interest still qualifies for the tax exemption, including bonds for affordable housing, nonprofit hospitals, and certain infrastructure projects.3Internal Revenue Service. Publication 4078 – Tax-Exempt Private Activity Bonds
Even when a qualified private activity bond’s interest escapes the regular income tax, it can still be a preference item for AMT purposes. Interest on most private activity bonds issued after August 7, 1986, gets added back to income when calculating AMT.4Office of the Law Revision Counsel. 26 USC 57 – Items of Tax Preference Exceptions apply to bonds financing qualified residential rental projects, qualified mortgage bonds, qualified veterans’ mortgage bonds, and bonds issued by 501(c)(3) nonprofits. A municipal bond fund’s annual statement breaks out how much of its income came from private activity bonds subject to AMT, and you need that figure when filing.
Tax-Exempt Interest That Still Raises Your Tax Bill
Because municipal bond interest does not count as gross income for the regular tax, it can feel invisible. Several other calculations pull it back in, and this is where planning around municipal bonds most often goes wrong.
Social Security Benefits
Whether Social Security benefits get taxed depends on “provisional income,” which is your adjusted gross income plus half your benefits plus any tax-exempt interest.5Office of the Law Revision Counsel. 26 USC 86 – Social Security and Tier 1 Railroad Retirement Benefits Above $25,000 for a single filer or $32,000 for a married couple filing jointly, up to 50% of benefits become taxable. Above $34,000 (single) or $44,000 (married filing jointly), up to 85% is taxable.6Internal Revenue Service. Social Security Income A retiree collecting $40,000 in municipal bond interest may assume it does not touch the tax return, but that $40,000 lifts provisional income and can pull thousands of dollars of benefits into taxable territory. The bonds themselves stay tax-free; the tax lands on the benefits.
Medicare Premium Surcharges
Medicare Part B and Part D premiums climb for higher-income beneficiaries through the Income-Related Monthly Adjustment Amount. That calculation uses your modified adjusted gross income from two years earlier, and tax-exempt interest is included. The surcharges start above $109,000 for single filers and $218,000 for married couples filing jointly in 2026, and each tier above those thresholds adds progressively higher monthly costs. A dollar over the threshold triggers the surcharge for the entire year, so a large municipal bond portfolio can push you into a higher premium bracket without adding anything to taxable income.
ACA Premium Subsidies
Eligibility for premium tax credits on the ACA marketplace also depends on modified adjusted gross income, which includes tax-exempt interest. Early retirees not yet on Medicare sometimes load up on municipal bonds for tax-free income without realizing that same income can reduce or wipe out their premium subsidy. The subsidy loss can outweigh the tax savings from the bonds.
Selling Before Maturity: Gains, Discounts, and Premiums
The exemption covers only interest. Selling a municipal bond for more than you paid produces a capital gain that is fully taxable at regular federal and state capital gains rates. Holding for more than one year gets you the lower long-term rate.
The De Minimis Rule on Market Discounts
Buying a bond on the secondary market below its face value creates a market discount, and the size of the discount changes how it is taxed. The threshold is 0.25% of face value multiplied by the number of full years remaining until maturity. If the discount is smaller than that amount, gain when you sell or redeem is treated as a capital gain. If the discount is larger, the gain attributable to the discount is taxed as ordinary income.
On a $10,000 bond with 10 years to maturity, the de minimis amount is $250. Buy at $9,800 and the $200 discount stays inside the cutoff, so it gets capital gains treatment. Buy at $9,700 and the $300 discount blows past the cutoff, and the full discount is taxed as ordinary income at redemption. Paying slightly more for a bond can leave you with more after taxes.
Bonds Bought at a Premium
When you buy a tax-exempt bond above face value, you must amortize the premium over the remaining life of the bond. Unlike taxable bonds, where you can elect to deduct the amortized premium against interest income, tax-exempt bonds give no deduction for the premium.7Office of the Law Revision Counsel. 26 US Code 171 – Amortizable Bond Premium Your cost basis still drops by the amortized amount each year, so if you sell later, your taxable gain will be larger (or your deductible loss smaller) than the original purchase price alone would suggest. Skipping premium amortization is a common and expensive mistake.
Comparing to Taxable Bonds
A 4% municipal bond and a 5% corporate bond are closer than they look. Because you keep all of the municipal interest but give up a share of the corporate interest to taxes, you have to convert the municipal yield to a comparable taxable number. Divide the municipal yield by one minus your marginal tax rate.
An investor in the 24% bracket holding a bond yielding 4% would calculate 4% ÷ (1 − 0.24) = 5.26%. The municipal bond matches a taxable bond paying 5.26%. A corporate bond of similar credit quality paying less than that leaves you worse off after taxes. For someone in the 37% bracket, the same 4% municipal equates to 6.35% taxable.
If you live in a state with income tax and hold an in-state bond, add state tax savings for a higher equivalent yield. The adjusted formula uses your combined marginal rate: municipal yield ÷ (1 − federal rate − state rate × (1 − federal rate)). In high-tax states, modest-looking municipal yields often produce equivalent taxable returns that investment-grade corporate debt cannot match.
Reporting on Your Tax Return
Your broker sends Form 1099-INT each year showing how much tax-exempt interest you received.8Internal Revenue Service. Topic No. 403, Interest Received Even though the interest is not federally taxed, the IRS requires you to report it. Tax-exempt interest goes on Line 2a of Form 1040, and any taxable interest on Line 2b.9Internal Revenue Service. Instructions for Schedule B (Form 1040) The IRS uses the Line 2a figure to check eligibility for various income-tested benefits and credits, which is exactly why the Social Security and Medicare effects described above can happen even when the interest itself is untaxed.
If any of your municipal bond interest comes from private activity bonds subject to AMT, that amount goes on Form 6251, Line 2g.10Internal Revenue Service. Form 6251 – Alternative Minimum Tax – Individuals Your 1099-INT breaks out AMT-subject interest in Box 9, so you do not have to sort the bonds yourself. If you also have a brokerage account generating more than $1,500 of taxable interest in the same year, file Schedule B with your 1040.