How does the tax treatment of municipal bonds work, and what is the tax-equivalent yield?

Municipal bond tax treatment is a classic Level I fixed income topic and essential for understanding relative value in the US bond market.

Tax Treatment of Municipal Bonds:

Federal Tax Exemption:

• Interest income from municipal bonds is generally exempt from federal income tax
• This applies to bonds issued by states, cities, counties, and their agencies
• Capital gains on munis are still taxable

State Tax Exemption (Double Tax-Free):

• If you buy a muni issued in your state of residence, interest is usually exempt from both federal AND state income taxes
• Example: A New York resident buying a New York City GO bond pays zero income tax on the coupon

Triple Tax-Free:

• Some jurisdictions exempt munis from local income taxes too (federal + state + local)

The Tax-Equivalent Yield (TEY) Formula:

TEY = Municipal Yield / (1 - Marginal Tax Rate)

This converts the tax-free muni yield into a pre-tax equivalent for comparison with taxable bonds.

Worked Example:

Investor profile: Claudia, California resident, 37% federal bracket, 13.3% state bracket

Combined marginal rate: 1 - (1-0.37)(1-0.133) = 1 - (0.63 x 0.867) = 1 - 0.5462 = 45.38%

California muni bond yielding 3.80%:

TEY = 3.80% / (1 - 0.4538) = 3.80% / 0.5462 = 6.96%

Comparable taxable corporate bond yielding 6.50%:

Claudia should buy the muni — its tax-equivalent yield (6.96%) exceeds the corporate bond yield (6.50%).

Muni Bond Types:

Important Nuances:

1. Alternative Minimum Tax (AMT) — Some private activity munis are subject to AMT
2. Build America Bonds — Special taxable munis with federal subsidy (no longer issued but still trading)
3. De minimis rule — If bought at a deep discount, the gain may be taxed as ordinary income, not capital gains

Exam Tip: The exam will always give you the tax rate. Your job is to apply the TEY formula correctly. Remember that the higher the investor's tax bracket, the more valuable the muni tax exemption becomes — this is why high-income investors are the primary muni market.

Practice TEY calculations in our CFA Level I question bank.