Taxable-Equivalent Yield

What it measures

Taxable-equivalent yield answers one question: what would a fully taxable bond have to yield for a given investor to keep the same amount after tax as a tax-exempt bond leaves them? It exists because yields are quoted before tax while the income is spent after tax, and municipal interest, Treasury interest, and ordinary taxable interest are each taxed on different terms.

The result is personal rather than universal. It depends on the investor's federal marginal rate, their state rate, whether the interest in question also escapes state tax, and whether the net investment income tax applies to their income level. Change any one input and the figure changes.

Nothing pays a taxable-equivalent yield. It is a hurdle rate — the return a taxable alternative would need to clear to match the tax-exempt bond, not an income stream anyone receives. The same arithmetic can run in reverse, computing an after-tax yield on the taxable bond and comparing it directly to the muni's stated yield; both directions produce the same ranking.

The concept applies wherever tax character differs: municipal bonds, generally exempt from federal tax; Treasuries and certain agency issuers, exempt from state and local tax; and everything else, fully taxable at the investor's ordinary rate.

How it is calculated

The basic formula is taxable-equivalent yield equals tax-exempt yield divided by one minus the marginal tax rate. As illustrative arithmetic only, not a market quote: a 3.00% federally exempt yield for a taxpayer in the 32% federal bracket works out to 3.00 divided by (1 minus 0.32), or 4.41%.

For an in-state municipal bond exempt at both federal and state levels, the divisor becomes one minus federal rate minus state rate, or more precisely (1 minus federal rate) multiplied by (1 minus state rate) when state tax is itself federally deductible. The simpler additive version is close enough for a quick screen but slightly overstates the benefit.

For a Treasury, which is taxable federally but exempt from state tax, the calculation runs the other way: a bank CD's after-state-tax yield is the CD yield multiplied by (1 minus state rate), and that adjusted figure is what gets compared against the Treasury's stated yield.

The 3.8% net investment income tax applies to taxable interest above statutory income thresholds but not to municipal interest, so it belongs inside the marginal rate used in this formula. The rate used throughout should be the marginal rate — the rate on the next dollar of income — never the average or effective rate, which would understate the exemption's value.

How to read it

The higher an investor's marginal rate, the higher the taxable-equivalent yield works out to be, which is part of why municipal bond yields are effectively set by the demand of high-bracket taxable buyers rather than by tax-exempt investors. The break-even bracket is the rate at which the muni's taxable-equivalent yield equals the taxable bond's actual yield; below that bracket the taxable bond wins after tax, above it the muni wins.

Credit quality and maturity have to be held constant for the comparison to mean anything. Running a taxable-equivalent calculation between a BBB revenue bond and a Treasury is a credit-risk comparison dressed up as a tax comparison.

Inside a tax-deferred account — a traditional IRA or 401(k) — the whole calculation collapses, because nothing held there is currently taxed. A tax-exempt yield in that setting is simply a lower yield with no offsetting benefit.

Fund-level detail matters too. A national municipal bond fund's income is exempt federally but largely taxable at the state level outside the investor's own state of residence, and a government money-market fund publishes each January the percentage of its prior year's income attributable to direct US government obligations, which affects state-tax treatment. The comparison also covers income only — tax-exempt interest still counts toward the income tests that determine how much of a Social Security benefit is taxable and whether Medicare premium surcharges apply.

Where it misleads

The most common error is quoting a single taxable-equivalent yield as if it applied to everyone. Marketing material almost always uses the top federal bracket, which flatters the number for the great majority of readers who are not in it.

Omitting state tax distorts the comparison in both directions — it understates the benefit of an in-state municipal bond and overstates the benefit of a national municipal fund held by a resident of a high-tax state.

The alternative minimum tax can break the premise entirely for some holders. Interest on certain private-activity municipal bonds counts as an AMT preference item, so for a taxpayer subject to AMT the supposedly exempt yield is not actually exempt.

Capital gains sit entirely outside the formula. A municipal bond bought at a discount in the secondary market can generate ordinary taxable income under the market-discount rules, which the taxable-equivalent calculation never accounts for. And using this comparison to weigh a municipal bond against a bank deposit hides a more fundamental difference — one is an insured deposit with no market price, the other a credit instrument that can lose value. Finally, the whole exercise is a snapshot: brackets change with legislation and with the investor's own income, so a comparison valid today can stop holding the moment either changes.

Where you will meet it on this site

This calculation appears on municipal bond pages, where every quoted yield is worth restating in taxable terms before it is measured against anything else. It appears on the cash rates page, where Treasury bills and bank CDs differ from each other by exactly this state-tax treatment.

It shows up in money-market fund comparisons, where government, prime, and tax-exempt funds cannot be ranked on their stated seven-day yields alone. More broadly, wherever this site uses the phrase after tax, this is the arithmetic sitting behind it — and it pairs naturally with yield to maturity, which is the pre-tax figure this calculation converts.