A double tax-exempt bond is a municipal bond whose interest is free from both federal income tax and the income tax of the state where you live, which happens when a state or local government in your own state issues the bond. The federal piece comes from Internal Revenue Code Section 103; the state piece comes from your state’s own rules, which almost always exempt interest on bonds issued within its borders for its residents. Combined, the two exemptions can lift after-tax yields meaningfully for higher-bracket investors. The exemption is narrower than it sounds, though: it covers interest only, a handful of states tax their own bonds, and tax-exempt interest still shows up in the formulas that decide how much of your Social Security is taxed and what you pay for Medicare.
The Federal Half of the Exemption
Section 103 of the Internal Revenue Code excludes from gross income the interest on any state or local bond.1Office of the Law Revision Counsel. 26 USC 103 – Interest on State and Local Bonds “State or local bond” means an obligation issued by a state or a political subdivision such as a city, county, school district, or water authority. Because the exclusion sits in federal law, it applies the same way in every state and to every investor, regardless of where the bond was issued or where the holder lives.
The exclusion covers interest and nothing else. Capital gains, market discount, and certain other income tied to municipal bonds can still create a federal tax bill, which is where a lot of investors get tripped up.
The State Half Depends on Where You Live
Most states exempt interest on bonds issued by their own government entities when the bondholder is a resident of the state. That residency requirement is what turns an ordinary muni into a double tax-exempt bond for you specifically. Buy a bond from a city, county, or agency in your own state, and the interest typically escapes state income tax as well. Buy one from across the state line, and that interest normally lands on your state return as taxable income.
Residency here means the state you actually live in and file a resident return in. If your state revenue department questions the exemption, you may need to back up your resident status with a driver’s license, voter registration, or proof of a permanent home. Claiming an in-state exemption on out-of-state bonds can produce back taxes and interest penalties.
States That Tax Their Own Bonds
A small group of states breaks the general pattern and taxes interest even on bonds issued by their own local governments. Recent surveys put roughly half a dozen states in this category, including Illinois, Iowa, Kansas, Oklahoma, and Wisconsin. If you live in one of these states, an in-state bond does not automatically deliver a state exemption, and the “double” label may not apply. Check your state’s current treatment before you assume it does.
States With No Income Tax
Nine states impose no state income tax at all: Alaska, Florida, Nevada, New Hampshire, South Dakota, Tennessee, Texas, Washington, and Wyoming. Residents there still get the federal exclusion, but there is no state tax to exempt in the first place, so the “double” concept does not really apply. The practical upside is that you can shop for municipal bonds from any state without giving up a state benefit you never had.
What the Exemption Does Not Cover
Three situations regularly generate federal tax on a bond whose interest is otherwise tax-free.
Capital Gains When You Sell
If you sell a municipal bond before maturity for more than you paid, the profit is a capital gain and it is taxable. Section 103 exempts interest, not price appreciation. This bites investors who buy when rates are high and sell after rates fall, since the bond’s market price rises above their cost. Bonds held one year or less produce short-term gains taxed at ordinary rates; bonds held longer get long-term capital gains rates.
Market Discount and the De Minimis Rule
Buying a municipal bond on the secondary market for less than face value creates “market discount.” When you eventually sell or redeem the bond, that discount can be taxed as ordinary income rather than as a capital gain. The dividing line is the de minimis rule: 0.25% of face value multiplied by the number of full years remaining to maturity. A discount below that threshold is treated as a capital gain; a discount above it is ordinary income at your marginal rate.2Municipal Securities Rulemaking Board. Tax and Liquidity Considerations for Buying Discount Bonds
A quick example. A $10,000 bond with 10 years left has a de minimis threshold of $250 (0.25% × $10,000 × 10). Pay $9,800 and the $200 discount falls under the threshold, so any gain is a capital gain. Pay $9,700 and the $300 discount clears the threshold, so the accrued portion is ordinary income.
Private Activity Bonds and the AMT
Not every muni qualifies under Section 103. The statute carves out private activity bonds that are not “qualified bonds,” arbitrage bonds, and bonds not issued in registered form.1Office of the Law Revision Counsel. 26 USC 103 – Interest on State and Local Bonds Private activity bonds are issued by a government but mainly benefit a private business, such as a stadium or industrial project, and they only stay tax-exempt if they fit specific categories in the code.3Office of the Law Revision Counsel. 26 USC 141 – Private Activity Bond; Qualified Bond
Even when a private activity bond is federally tax-exempt, its interest is often a preference item for the Alternative Minimum Tax. Interest on qualified private activity bonds issued after August 7, 1986, generally counts as an AMT preference, with carve-outs for qualified residential rental projects, qualified mortgage bonds, qualified veterans’ mortgage bonds issued after July 30, 2008, and qualified 501(c)(3) bonds.4Internal Revenue Service. Publication 550 (2025) – Investment Income and Expenses Your 1099-INT breaks out the AMT-subject portion in Box 9 so you can see whether Form 6251 applies to you.
Tax-Exempt Interest Can Still Cost You Money
This is the quiet part. The IRS and the Social Security Administration both fold tax-exempt interest back into the formulas that decide how much of your Social Security is taxable and what you pay for Medicare.
Social Security Benefits
Whether your Social Security benefits are taxable turns on “provisional income”: adjusted gross income, plus half your Social Security benefits, plus all tax-exempt interest. The statute expressly adds back interest that is exempt from tax. If the total tops $25,000 for single filers or $32,000 for joint filers, part of your benefits becomes taxable.5Office of the Law Revision Counsel. 26 USC 86 – Social Security and Tier 1 Railroad Retirement Benefits A retiree who assumes muni interest is invisible to the IRS can end up owing tax on Social Security income they thought was safe.
Medicare Part B and Part D Surcharges
Medicare uses Modified Adjusted Gross Income to set the Income-Related Monthly Adjustment Amount, or IRMAA. MAGI for this purpose is adjusted gross income plus tax-exempt interest.6Social Security Administration. Modified Adjusted Gross Income (MAGI) For 2026, single filers with MAGI above $109,000 and joint filers above $218,000 pay surcharges on top of the standard Part B premium of $202.90 per month, with surcharges ranging from $81.20 to $487.00 per month depending on income.7Centers for Medicare and Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles Similar surcharges apply to Part D. A sizable muni portfolio can push a retiree over an IRMAA threshold and add thousands in annual Medicare costs, which quietly erodes some of the tax benefit.
One Extra Federal Break: The Net Investment Income Tax
Tax-exempt muni interest is not subject to the 3.8% Net Investment Income Tax that applies to higher-income taxpayers. The IRS confirms the NIIT does not reach income already excluded for regular income tax purposes, including tax-exempt state and municipal bond interest.8Internal Revenue Service. Topic No. 559 – Net Investment Income Tax For investors above $200,000 single or $250,000 joint, that preserves a real edge over taxable bonds, which would face both regular income tax and the 3.8% surtax.
Territory Bonds: The Triple Tax-Exempt Case
Bonds issued by Puerto Rico carry a broader exemption. Federal law makes all Puerto Rico government bonds exempt from federal, state, territorial, District of Columbia, and local taxation, so the interest is tax-free no matter where in the United States you live.9Office of the Law Revision Counsel. 48 USC 745 – Tax Exempt Bonds That is where the “triple tax-exempt” label comes from. Comparable exemptions exist for Guam, the US Virgin Islands, and the Northern Mariana Islands under their federal enabling statutes.10Congress.gov. H. Rept. 108-102 – To Clarify the Tax Treatment of Bonds Tax-exempt is not risk-free, though. Puerto Rico’s recent fiscal history is a reminder to weigh credit quality alongside the tax benefit.
Reporting the Interest on Your Return
You still have to report tax-exempt interest even though you do not pay federal tax on it. Reporting does not turn it into taxable income; the IRS uses the figure to run the Social Security and Medicare calculations described above and to verify eligibility for various credits.4Internal Revenue Service. Publication 550 (2025) – Investment Income and Expenses
Your broker sends a Form 1099-INT each year. Box 8 shows total tax-exempt interest paid to you.11Internal Revenue Service. Form 1099-INT – Interest Income Box 9 shows the portion of Box 8 that is subject to the AMT.4Internal Revenue Service. Publication 550 (2025) – Investment Income and Expenses You report the total on Form 1040, line 2a. If you bought a tax-exempt bond at a premium, you report the net amount after subtracting the amortized bond premium for the year.12Internal Revenue Service. Instructions for Schedule B (Form 1040) (2025)
For your state return, you have to split in-state interest from out-of-state interest. Brokerage year-end reports usually do this for individual bonds, but mutual funds and ETFs holding bonds from many states take more work. The fund company publishes an annual state-by-state breakdown of its tax-exempt income; you apply your home state’s percentage to figure the portion eligible for the state exemption. Getting that split wrong is one of the more common muni bond errors on state returns, and it can trigger back taxes and interest on the underpayment.