Tax-exempt interest income is interest paid on certain bonds — almost always state and local government bonds — that the federal government permanently excludes from your gross income under Internal Revenue Code Section 103.1Office of the Law Revision Counsel. 26 U.S. Code 103 – Interest on State and Local Bonds It is not deferred like a 401(k) withdrawal. It never enters your gross income in the first place. But it is not invisible. You still report it, and it still feeds into calculations that can tax your Social Security benefits, raise your Medicare premiums, and trigger the Alternative Minimum Tax.
Where Tax-Exempt Interest Comes From
Nearly all of it comes from the municipal bond market: bonds issued by states, cities, counties, school districts, and other political subdivisions to fund schools, highways, hospitals, and water systems. Section 103 defines a “state or local bond” as any obligation of one of those issuers, and the exclusion applies to the interest they pay.
General obligation bonds are backed by the issuing government’s full taxing power. Revenue bonds are repaid only from the income a specific project generates, such as bridge tolls or utility fees. Interest on both is generally exempt from federal income tax.
Two categories carry footnotes worth knowing.
Private activity bonds. Under IRC Section 141, a bond is a private activity bond when more than 10% of the proceeds fund a private business use and the bond also meets a private payment or security test.2Office of the Law Revision Counsel. 26 USC 141 – Private Activity Bond; Qualified Bond Bonds for a privately operated stadium, an industrial park, or certain housing developments are typical examples. Interest on qualified private activity bonds can still be exempt from regular federal income tax, but it becomes a preference item under the AMT.
U.S. territory bonds. Bonds issued by Puerto Rico, Guam, the U.S. Virgin Islands, and other U.S. territories are generally exempt from federal, state, and local income taxes nationwide.3Internal Revenue Service. Tax-Exempt Interest That triple exemption applies wherever you live.
The exclusion covers interest only. Selling a municipal bond for more than you paid produces a taxable capital gain at ordinary capital gains rates.4Municipal Securities Rulemaking Board. Understanding Taxable Municipal Bonds
How to Report It
Even though it does not count toward your gross income, the IRS still wants the number on your return.
If you hold individual municipal bonds, your bank or brokerage reports the interest on Form 1099-INT, Box 8, which is designated for tax-exempt interest.5Internal Revenue Service. Instructions for Forms 1099-INT and 1099-OID If you invest through a mutual fund or ETF, the fund reports your share as exempt-interest dividends on Form 1099-DIV, Box 12.6Internal Revenue Service. Instructions for Form 1099-DIV Box 13 of the same form breaks out the portion attributable to private activity bonds; keep that number, because you need it for the AMT calculation.
On Form 1040, total tax-exempt interest goes on Line 2a. Taxable interest goes on Line 2b. Skipping Line 2a does not save you any tax, and the IRS uses that figure to check AMT liability and to calculate how much of your Social Security is taxable.
Private Activity Bonds and the AMT
The Alternative Minimum Tax is a parallel calculation designed to keep high-income taxpayers from using exclusions and deductions to shrink their tax bill too aggressively. IRC Section 57 designates interest on specified private activity bonds as a tax preference item.7Office of the Law Revision Counsel. 26 U.S. Code 57 – Items of Tax Preference On Form 6251, that interest gets added back into your Alternative Minimum Taxable Income on Line 2g. If the resulting AMT exceeds your regular tax, you pay the higher amount.
The AMT applies at 26% on the first portion of income above the exemption and 28% on amounts above that.8Office of the Law Revision Counsel. 26 USC 55 – Alternative Minimum Tax Imposed For 2026, the AMT exemption is $90,100 for single filers (phasing out at $500,000 of AMTI) and $140,200 for married couples filing jointly (phasing out at $1,000,000).9Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026 For a taxpayer subject to the AMT, the tax-exempt status of private activity bond interest is effectively wiped out. Standard general obligation and revenue bond interest is not a preference item and does not trigger AMT.
How It Can Make Your Social Security Taxable
Under IRC Section 86, the IRS decides how much of your Social Security is taxable by computing what is commonly called provisional income: your adjusted gross income, plus half of your Social Security benefits, plus all tax-exempt interest.10Office of the Law Revision Counsel. 26 USC 86 – Social Security and Tier 1 Railroad Retirement Benefits Municipal bond interest counts here, even though it does not count toward regular income tax. That catches many retirees off guard.
The base amounts, set by statute and not indexed to inflation, are:
- $25,000 for single filers
- $32,000 for married couples filing jointly
- $0 for married individuals filing separately who lived with their spouse at any point during the year
Above those thresholds, up to 50% of benefits can be taxable. At the higher tier of $34,000 for single filers and $44,000 for joint filers, up to 85% becomes taxable.11Internal Revenue Service. Social Security Income A large muni portfolio can push you past those tiers without adding a dollar to your regular taxable income.
How It Can Raise Your Medicare Premium
Medicare Part B and Part D premiums are income-tested through the Income-Related Monthly Adjustment Amount, or IRMAA. The Social Security Administration calculates IRMAA using Modified Adjusted Gross Income, which is your AGI plus tax-exempt interest from Line 2a.12Social Security Administration. Modified Adjusted Gross Income (MAGI) The MAGI used for 2026 premiums comes from your 2024 tax return.
For 2026, the first IRMAA surcharge starts at $109,000 for single filers and $218,000 for joint filers. The standard Part B premium before any surcharge is $202.90 per month. At the highest tier, above $500,000 single or $750,000 joint, the combined Part B and Part D surcharges add hundreds of dollars per month. Retirees who hold substantial muni bond portfolios sometimes discover that their tax-free interest is producing real, monthly Medicare costs.
The One Place It Really Is Invisible: NIIT
The 3.8% Net Investment Income Tax does not apply to tax-exempt municipal bond interest. The IRS excludes it from the definition of net investment income.13Internal Revenue Service. Questions and Answers on the Net Investment Income Tax It is also not added to AGI when calculating the MAGI threshold that determines whether you owe NIIT at all.14Internal Revenue Service. Topic No. 559, Net Investment Income Tax For this calculation only, muni interest genuinely does not exist.
State Tax Treatment
Federal exemption does not automatically mean state exemption. Every state sets its own rule, and the answer usually turns on who issued the bond.
The general pattern: interest on bonds issued within your state of residence is exempt from that state’s income tax. A California resident who owns a bond issued by the City of Los Angeles typically pays no California tax on the interest. That “double exemption” from federal and state tax is why in-state munis are popular with investors in high-tax states.
Interest on bonds issued by other states is generally taxable in your home state. The same California resident holding an Arizona municipal bond would owe California tax on the interest, even though it stays federally exempt. A handful of states with no income tax make the in-state versus out-of-state distinction irrelevant. And bonds from U.S. territories, again, escape federal, state, and local tax anywhere in the country.
Capital Gains, OID, and Market Discount
The tax-exempt label applies to interest payments. Other income from a municipal bond position can be taxable, and one rule in particular catches people off guard.
- Capital gains. Selling a muni for more than your purchase price produces a taxable gain at ordinary capital gains rates, short-term or long-term depending on holding period.4Municipal Securities Rulemaking Board. Understanding Taxable Municipal Bonds
- Original issue discount. When a municipal bond is initially issued below face value, the difference accrues over the bond’s life. Under IRC Section 1288, accrued OID on a tax-exempt bond is treated as tax-exempt interest rather than taxable income.
- Market discount. If you buy an already-issued muni on the secondary market at a discount, the discount you later collect at maturity or sale is generally taxed as ordinary income. A de minimis rule applies: if the discount is less than 0.25% of face value multiplied by the full years remaining to maturity, the gain is treated as a capital gain instead.
If you buy discounted munis in the secondary market, run the de minimis calculation before assuming capital gains treatment.
Interest You Can’t Deduct
IRC Section 265 prohibits deducting interest on debt you incurred to buy or carry tax-exempt securities.15Office of the Law Revision Counsel. 26 USC 265 – Expenses and Interest Relating to Tax-Exempt Income The logic is that the government will not subsidize a deduction on borrowing costs when the resulting income is tax-free. If you take out a margin loan and use the proceeds to buy municipal bonds, the interest on that loan is not deductible. The rule applies broadly, including to financial institutions that hold muni inventories. As a practical matter, funding a muni purchase with borrowed money often produces non-deductible interest expense that swamps the tax advantage of the exempt income.