Compare tax-free muni yield to its taxable equivalent.
Tax-equivalent yield
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Comparing a tax-free yield to a taxable one
Municipal bonds pay interest that is exempt from federal income tax, and often from state tax too if you buy bonds issued in your own state. That tax break makes a muni's stated yield look low next to a taxable corporate or Treasury bond, but the comparison is unfair until you put both on the same after-tax footing. The tax-equivalent yield does exactly that: it tells you what a fully taxable bond would have to yield to leave you with the same money in your pocket after the IRS takes its cut. Once you have that number, you can shop munis and taxable bonds side by side.
The formula this tool uses is the standard one: divide the muni yield by the quantity one minus your combined marginal tax rate. The higher your tax bracket, the smaller that denominator, and the more a tax-free yield is worth. That is why munis are mainly a high-bracket instrument. For someone in the 10 or 12 percent federal bracket the boost is slight, and taxable bonds usually win outright on raw yield.
A 3.5 percent muni in a 37 percent combined bracket
Take the default: a 3.5 percent muni yield, a 32 percent federal marginal rate, and a 5 percent state rate. The tool adds the federal and state rates to a 37 percent combined marginal rate. Divide 3.5 percent by one minus 0.37, which is 0.63, and the tax-equivalent yield is about 5.556 percent. In plain terms, a taxable bond would need to yield 5.556 percent to match this tax-free 3.5 percent muni for this investor. If the best comparable taxable bond yields only 5 percent, the muni is the better buy even though its headline number looks smaller.
When the state line matters
The state rate field is where most people go wrong. If you buy a muni issued in the state where you live, the interest is usually exempt from both federal and state tax, the so-called double tax-free benefit, so you should include your state rate to capture the full advantage. But if you buy an out-of-state muni, your home state generally taxes that interest, so the state exemption does not apply and you should set the state rate to zero. Set it incorrectly and you will overstate how attractive the bond is. This is the single most useful judgment the tool helps you make.
One quiet edge case for high earners: muni interest is exempt from regular income tax but still counts toward modified adjusted gross income, which can raise the share of your Social Security benefits that gets taxed and can nudge Medicare premium surcharges higher. So a muni is not always perfectly invisible to the tax system. A separate wrinkle is that interest from certain private activity bonds can be a preference item for the alternative minimum tax, so very high-income investors should confirm a muni fund is AMT-free before assuming the yield is fully shielded.
Who this comparison is built for
This calculator is for an investor in a taxable brokerage account deciding between municipal and taxable bonds, or a saver in a high bracket weighing whether munis belong in their portfolio at all. The key insight to carry away: never compare a muni and a taxable bond on stated yield alone, because the muni's number is already after-tax while the taxable bond's is not. A practical rule of thumb is that munis tend to win once your combined marginal rate clears the low-30s, and they rarely make sense inside a tax-sheltered account like an IRA, where the tax exemption is wasted because the account is already shielded.
Should I use my marginal tax rate or my effective tax rate here?
Always the marginal rate, the rate on your next dollar of income. Bond interest stacks on top of everything else you earn, so each dollar of taxable interest is taxed at your top bracket, not at your blended average. Using your lower effective rate would understate the tax you actually pay on taxable interest and make taxable bonds look better than they are. The tool is built around the marginal rate for exactly this reason.
Are Treasury bonds taxed the same way as corporate bonds?
Not quite, and it affects the comparison. Treasury interest is fully taxable at the federal level but exempt from state and local income tax. So when you compare a muni against a Treasury, the Treasury already escapes state tax, which narrows the muni's edge in a high-tax state. Corporate bond interest, by contrast, is taxable at both federal and state levels, so it faces the full combined rate and is the cleanest case for the tax-equivalent yield comparison this tool runs.