Tax-Equivalent Yield

A tax-equivalent yield (TEY) is the yield-to-maturity that a taxable bond would need to offer in order to provide the same after-tax return as a tax-exempt municipal bond, given the investor’s marginal tax bracket. It converts a muni’s tax-free yield into a pre-tax equivalent, allowing direct comparison of muni bonds against taxable alternatives like corporate bonds or treasury bills.

The tax advantage of municipal bonds

Municipal bonds issued by states, cities, and other local authorities are exempt from federal income tax and, in most cases, state and local income tax (if the bondholder resides in the issuing state). A bond paying 3.5 percent interest delivers a full 3.5 percent after-tax return to a federal taxpayer, whereas a corporate bond paying 3.5 percent is taxable: a bondholder in the 37 percent federal bracket keeps only 2.21 percent after tax.

This tax advantage makes municipal bonds attractive to high-income earners and institutions in high tax brackets. But the comparison is not obvious on the surface: a muni yielding 3.5 percent looks lower than a corporate bond yielding 4.5 percent. Tax-equivalent yield translates the muni’s tax-free return into the taxable yield it would need to match, making the comparison clear.

The calculation

The formula is straightforward:

Tax-Equivalent Yield = Municipal Yield ÷ (1 − Marginal Tax Rate)

Suppose a muni bond yields 3.5 percent and an investor’s federal marginal tax rate is 37 percent. The tax-equivalent yield is:

3.5% ÷ (1 − 0.37) = 3.5% ÷ 0.63 = 5.56%

This means a taxable bond would need to yield 5.56 percent to provide the same after-tax return as the 3.5 percent muni. If the taxable bond actually yields only 4.5 percent, the muni is the better choice.

For lower-income investors, the calculation looks different. An investor in the 24 percent bracket sees:

3.5% ÷ (1 − 0.24) = 3.5% ÷ 0.76 = 4.61%

The tax-equivalent yield is lower, and the tax advantage of the muni is correspondingly smaller. At very low incomes or zero tax-bracket, the muni offers no advantage, and a taxable bond may be preferable if it offers a higher nominal yield.

State and local taxes add complexity

Many states impose income tax on municipal bonds issued in other states but exempt in-state bonds from state tax. A New York resident buying a California muni must pay California state income tax on the interest; the same resident buying a New York muni pays neither federal nor state tax.

To account for this, investors and advisers often use an after-tax equivalent yield that includes both federal and state rates:

Tax-Equivalent Yield (with state tax) = Municipal Yield ÷ (1 − Federal Rate − State Rate + (Federal Rate × State Rate))

The formula accounts for the federal deduction of state taxes (in some jurisdictions) or, more commonly, simply stacks them. A 3.5 percent muni, evaluated by a New York resident, might assume a combined marginal rate of 37 percent federal plus 6.85 percent New York state—roughly 41 percent combined (ignoring phase-outs and deduction limits), yielding a tax-equivalent yield around 5.93 percent.

Practical use in bond selection

Professional investors and advisers calculate tax-equivalent yield routinely to benchmark municipal bonds against taxable alternatives. A pension fund or insurance company in a low tax bracket may find that taxable bonds dominate; a high-earner’s financial planner will stress municipal bonds as tax-efficient core holdings.

Market prices reflect these calculations implicitly. When high earners flock to munis, yields fall (prices rise), lowering the muni’s tax-equivalent yield. When taxable bond yields spike, the tax-exempt advantage of munis shrinks. The intersection of supply and demand sets the equilibrium spread.

Municipal bond market participants watch the “muni-to-Treasury ratio”—the ratio of muni yields to equivalent-maturity Treasury yields—as a broad indicator of relative value. When munis trade at a 70 percent ratio to Treasuries (e.g., a 5-year muni at 2.5 percent, 5-year Treasury at 3.6 percent), high-bracket investors will calculate whether the tax saving justifies the lower nominal yield.

Who benefits most

Investors in the 35 percent-plus federal bracket (primarily high earners and some institutions) almost always find municipal bonds attractive on a tax-equivalent-yield basis. Investors in the 22–24 percent brackets may or may not, depending on state taxes and the specific spread between muni and taxable yields at any given moment.

Investors in the 12 percent bracket or lower typically find that taxable bonds offer better nominal yields, and the tax advantage of munis does not compensate. Tax-exempt accounts (IRAs, 401k plans, trusts) have no tax advantage from owning munis and should focus purely on yield and credit risk.

Some investors deliberately compare individual municipal and taxable bonds using this formula to ensure they are not overpaying for tax-exempt status or missing a tax-advantaged opportunity.

See also