Tax equivalent yield is the interest rate a taxable bond would have to pay to leave you with the same after-tax income as a tax-exempt bond. You calculate it by dividing the tax-free yield by one minus your marginal tax rate. An investor in the 24% federal bracket looking at a municipal bond paying 3% would need a taxable bond paying about 3.95% to come out even. The higher your bracket, the wider that gap gets, and the more the calculation matters.
The Formula and a Worked Example
There is one moving part. Take the tax-exempt yield and divide it by (1 − your marginal tax rate).
Say you’re in the 32% bracket and looking at a municipal bond yielding 3.5%. Subtract 0.32 from 1.00 to get 0.68, then divide 0.035 by 0.68. The answer is roughly 5.15%. A taxable corporate bond has to pay more than 5.15% before it beats that 3.5% muni for you.
The formula works because federal law excludes interest on state and local government bonds from gross income.1Office of the Law Revision Counsel. 26 USC 103 – Interest on State and Local Bonds A corporate bond paying 5% doesn’t actually deliver 5% to a 32% bracket investor. It delivers about 3.4% after federal tax. Tax equivalent yield surfaces that gap without forcing you to do after-tax math on every taxable bond you consider.
Round numbers help show how much the bracket drives the result. A 4% tax-free yield converts to 4% ÷ 0.65 = 6.15% for someone in the 35% bracket. The same 4% muni converts to only 4.55% for someone in the 12% bracket. Same bond, wildly different value depending on who owns it.
Use Your Marginal Rate, Not Your Effective Rate
The most common mistake is plugging in the wrong tax rate. You want your marginal rate, meaning the percentage that applies to your next dollar of income. Not your effective rate, which averages tax across everything you earn. Investment interest stacks on top of wages and salary, so it gets taxed at whatever bracket that top layer sits in.
For 2026, federal income tax rates run from 10% to 37%.2Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026 Someone at 37% gets a tax equivalent yield of about 6.35% on a 4% muni. Someone at 12% gets 4.55% on the same bond. The higher your bracket, the more the exemption is worth to you.
Adding State Income Tax
The basic formula only handles federal tax. Many investors also owe state income tax on investment earnings, and municipal bonds issued within your home state are generally exempt from that state’s income tax as well.3Municipal Securities Rulemaking Board. Municipal Bond Basics When both exemptions apply, fold your state rate into the calculation.
The simple approach adds your federal and state marginal rates and uses the combined figure. Federal 24% plus state 6% gives you 30%, so you divide the tax-free yield by 0.70. A 3% muni now converts to about 4.29% rather than 3.95%. That difference is enough to flip the decision on a close call.
This simple addition slightly overstates the benefit if you itemize and can deduct state income taxes on your federal return, because federal and state taxes interact. The more precise formula is 1 − (1 − federal rate) × (1 − state rate). For 2026, the deduction for state and local taxes is capped at $40,000 for most filers with income under $500,000, so investors already at or above that cap get no extra federal benefit from state tax paid on investment income, and the simple addition is accurate for them. For screening purposes, the simple method usually gets you close enough.
The 3.8% Net Investment Income Tax
Higher-income investors owe an additional 3.8% Net Investment Income Tax on top of regular income tax. It applies once modified adjusted gross income exceeds $200,000 for single filers or $250,000 for married couples filing jointly, and it hits the lesser of your net investment income or the amount your income runs over the threshold.4Office of the Law Revision Counsel. 26 USC 1411 – Imposition of Tax
Interest from taxable bonds counts as net investment income. Interest from tax-exempt municipal bonds does not. So for someone above the MAGI threshold, the effective federal rate on taxable bond interest is the marginal rate plus 3.8%. An investor in the 35% bracket who also owes the NIIT faces 38.8% on taxable bond income. Run that through the formula and a 4% muni converts to 4% ÷ 0.612 = about 6.54%. That’s a meaningful jump from the 6.15% figure you’d calculate on the 35% bracket alone.
If you’re anywhere near the NIIT income thresholds, run the calculation both ways to see how much the surtax shifts the answer. Standard bracket tables don’t show it.
Which Yield Number to Plug In
The coupon rate printed on a bond tells you what percentage of face value you receive each year in interest, but it doesn’t account for the price you actually paid. If you bought at a premium or a discount, yield to maturity is the better figure because it reflects total return over the bond’s remaining life.
Callable bonds add a layer. If the issuer can redeem the bond early, yield to call may be lower than yield to maturity. Conservative practice is to use the lower of the two, sometimes called yield to worst, because that’s the minimum you should expect. Running the tax equivalent yield calculation on an optimistic yield figure defeats the point.
When the Calculation Says Don’t Bother
The formula works in both directions. If a muni’s tax equivalent yield barely beats a comparable taxable bond, the muni may not be worth it. Municipal bonds tend to be less liquid than Treasuries or large corporate issues, and credit risk on some municipal issuers is real. A thin yield edge doesn’t cover those drawbacks.
Investors in the 10% or 12% brackets rarely benefit from tax-exempt bonds. At 12%, a 3% muni converts to just 3.41%, which taxable bonds of similar credit quality often clear comfortably. Tax equivalent yield is most useful in the 32% bracket and above, where the conversion factor opens a spread taxable alternatives struggle to match.
Tax-advantaged accounts change the picture completely. Municipal bonds held inside an IRA or 401(k) gain nothing from tax-exempt status because the account already shelters income from current tax. Holding munis in a tax-deferred account wastes the exemption and accepts a lower coupon for it. The calculation only applies to bonds held in taxable brokerage accounts.
Situations That Distort the Result
A clean tax equivalent yield calculation assumes the bond’s interest is fully tax-exempt and nothing else in your return is affected by holding it. A few situations break those assumptions.
Interest on certain private activity bonds, used for projects like hospitals, affordable housing, and airports, is a tax preference item under the Alternative Minimum Tax. If the AMT applies to you, that interest gets added back into income for the AMT calculation and the exemption is partly or fully erased. Bonds issued by nonprofits under section 501(c)(3) and certain housing bonds are carved out.5Office of the Law Revision Counsel. 26 USC 57 – Items of Tax Preference If a bond is labeled as a private activity bond and you’re anywhere near AMT territory, don’t assume the full exemption applies.
Buying a muni on the secondary market at a discount can trigger tax when the bond matures or is sold. The dividing line, sometimes called the de minimis rule, is 0.25% of face value per full year to maturity. Below that threshold, the gain is taxed at capital gains rates. Above it, the gain is taxed as ordinary income, which is a meaningfully higher rate for most investors. Part of the current market yield you’re using in the formula may end up taxed as ordinary income, so the true tax equivalent yield is lower than the formula suggests. Check the purchase price against this threshold before plugging numbers in.
Retirees should know one more wrinkle. Tax-exempt municipal bond interest gets added back to income when the IRS calculates how much of your Social Security benefits are taxable.6Office of the Law Revision Counsel. 26 USC 86 – Social Security and Tier 1 Railroad Retirement Benefits The interest itself stays untaxed, but it can push more of your benefits into taxable territory, up to 85%. The standard formula doesn’t capture this indirect cost, so the true value of munis for a retiree drawing Social Security is slightly lower than the calculation implies.