Municipal Bonds Explained: Tax-Free Income, Credit Risk and Yields
Municipal bonds fund roads, schools, bridges and water systems, and their interest is often exempt from federal income tax. This guide explains general obligation and revenue bonds, how to compare a muni yield with a taxable one, credit ratings, call risk, the AMT and the tax details investors often miss.
When a city rebuilds a water plant, a state expands a university or a toll authority builds a bridge, it often borrows the money by selling municipal bonds. The Golden Gate Bridge itself was financed with bonds that voters in the bridge district approved in 1930. For investors, "munis" offer something most bonds don't: interest that is usually exempt from federal income tax. That single feature shapes who buys them, how they're priced and how they should be compared with other bonds.
What a municipal bond is
A municipal bond is a loan to a state or local government or one of its agencies: cities, counties, school districts, hospital and transit authorities, airports, utilities and more. Like other bonds, it pays interest (usually twice a year) and returns the face value at maturity. Maturities run from a year or less to 30 years or longer.
Munis fall into two main families:
- General obligation (GO) bonds are backed by the issuer's general taxing power. Repayment depends on the overall finances of the city, county or state.
- Revenue bonds are repaid from a specific income stream: tolls, water and sewer fees, airport charges, hospital revenue or a dedicated sales tax. Their safety depends on how reliable that stream is.
| Feature | General obligation bonds | Revenue bonds |
|---|---|---|
| Backed by | Issuer's taxing power | A specific project or revenue source |
| Key risk | Weak finances of the whole government | The project earning less than expected |
| Voter approval | Often required | Usually not required |
| Typical issuers | States, cities, counties, school districts | Utilities, toll roads, airports, hospitals |
The tax advantage, and its limits
Interest on most munis is exempt from federal income tax. Many states also exempt interest on bonds issued within that state for their own residents, while taxing bonds from other states. The exact rules vary, so check your state's revenue department.
Several details catch investors out:
- Taxable munis exist. Some municipal bonds are issued as federally taxable, for example when they fund projects that don't qualify for the exemption.
- Private activity bonds fund projects with significant private involvement, such as some airports, housing or industrial projects. Interest on certain of these can be subject to the alternative minimum tax (AMT).
- Capital gains are taxable. If you sell a muni for more than you paid, or buy one below face value and it matures at par, the gain may be taxed. Under the IRS "market discount" rules, part of that gain can be taxed as ordinary income rather than at capital gains rates.
- Tax-exempt interest still gets reported. It appears on your Form 1040, and it is included when calculating how much of your Social Security benefits is taxable and when Medicare determines whether you owe higher premiums based on income. Our guide to how retirement income is taxed walks through those calculations.
IRS Publication 550 covers the treatment of tax-exempt interest and market discount in detail.
How to compare a muni yield with a taxable yield
Because munis are tax-advantaged, they usually yield less than Treasuries or corporate bonds of similar maturity and quality. The useful comparison is the taxable-equivalent yield: the yield a taxable bond would need to offer to leave you with the same after-tax income.
The basic formula:
Taxable-equivalent yield = muni yield ÷ (1 − your federal marginal tax rate)
As an illustration, a muni yielding 3% for an investor in a 32% federal bracket has a taxable-equivalent yield of about 4.4% (3 ÷ 0.68). If the investor also avoids state income tax, the equivalent yield is higher still. For someone in a low bracket, the same muni's equivalent yield is only slightly above 3%, which is why munis tend to appeal most to people in higher brackets.
The calculation uses your marginal rate, the rate on your next dollar of income, not your average rate. Federal brackets change each year; the IRS publishes them at irs.gov.
Credit quality and ratings
Moody's, S&P Global Ratings and Fitch assign credit ratings to many municipal bonds, from the highest grades (AAA/Aaa) down through the investment-grade tiers to below-investment-grade, or "high-yield," munis. Lower ratings generally mean higher yields to compensate for greater default risk.
Things that weigh on a muni's credit include:
- A shrinking population or tax base
- Heavy pension and retiree health obligations
- Reliance on a single employer or industry
- For revenue bonds, falling usage of the project (fewer tolls, fewer patients, lower water sales)
Some bonds carry bond insurance, in which a private insurer guarantees payments if the issuer can't pay. The protection is only as strong as the insurer.
Every new municipal issue comes with an official statement, which is the muni equivalent of a prospectus, and issuers file ongoing financial disclosures. Both are free on the Municipal Securities Rulemaking Board's EMMA website, along with recent trade prices.
Interest rate and call risk
Munis respond to interest rates like any other bond: when market rates rise, existing bond prices fall, and longer maturities fall more. Our explainer on why bond prices fall when rates rise covers duration in more detail. If you hold an individual bond to maturity and the issuer pays, interim price swings don't change what you receive.
Many munis are callable: the issuer can repay them early, often starting around ten years after issue. Issuers tend to call bonds when rates have fallen, which is exactly when reinvesting the money is least attractive. For callable bonds, look at the yield to worst, which assumes the least favorable call or maturity date, not just the yield to maturity.
Ways to own munis
- Individual bonds. Bought through a brokerage, often in $5,000 face-value increments. They give control over maturity and issuer, but the market is fragmented and many bonds trade infrequently. Dealers earn a markup, which they must disclose on many retail trade confirmations, and small orders can carry wide spreads. Check recent trades on EMMA before buying.
- Municipal bond mutual funds and ETFs. They offer instant diversification across hundreds of issuers, professional credit research and daily liquidity. They have no maturity date, so the fund's price moves with rates indefinitely, and they charge an annual expense ratio.
- Single-state funds. These hold bonds from one state, aiming for both federal and state tax exemption for residents, in exchange for less geographic diversification.
- Separately managed accounts. These are offered by advisors for larger balances, with bonds held directly in your name.
Who munis typically suit
Munis are most often considered by investors who hold bonds in taxable accounts and are in higher tax brackets, including retirees seeking steady income. They generally make little sense inside IRAs, 401(k)s and other tax-sheltered accounts, where the exemption adds nothing.
Whether they fit a particular portfolio depends on the tax bracket, state of residence, the time horizon and how much credit and rate risk the investor can accept. Run the taxable-equivalent yield calculation with your own numbers, read the official statement for any individual bond, and use EMMA to see what a bond has actually traded for before you place an order.
Frequently asked questions
Are municipal bonds completely tax-free?
Not always. Interest on most municipal bonds is exempt from federal income tax, and often from state tax if you live in the issuing state, but some munis are federally taxable and some private activity bonds can trigger the alternative minimum tax. Any capital gain when you sell or redeem a bond above your cost is generally taxable, and tax-exempt interest still counts in some income calculations, such as the one used to tax Social Security benefits.
Do municipal bonds make sense in an IRA or 401(k)?
Generally they are a poor fit. Retirement accounts already shelter interest from current tax, and withdrawals from traditional accounts are taxed as ordinary income, so the muni tax exemption is wasted while you usually accept a lower yield. Munis are typically considered for taxable brokerage accounts.
Can a city or state default on its bonds?
Yes, although defaults among rated municipal issuers have historically been uncommon compared with corporate bonds. Detroit's bankruptcy in 2013 and Puerto Rico's debt crisis are well-known examples where bondholders took losses. Credit ratings, the issuer's disclosures on the MSRB's EMMA website and diversification are the main tools investors use to manage the risk.
