Tax-Equivalent Yield Calculations

Municipal bond yields look lower than taxable alternatives, but the comparison is meaningless without adjusting for taxes. A 3% municipal yield in a 30% combined tax bracket equals a 4.28% taxable equivalent—and once you’re in the 37% federal bracket plus state and NIIT, the same 3% muni equates to over 6% taxable. The point is: you need to compare after-tax returns, and the math isn’t complicated once you understand the formula.

The Core Formula (What You’re Actually Calculating)

Tax-equivalent yield converts a tax-exempt municipal bond yield into the pretax yield a taxable bond would need to offer to produce the same after-tax return.

The formula:

Tax-Equivalent Yield = Municipal Bond Yield / (1 - Total Tax Rate)

Why it works: You’re solving for the taxable yield that, after taxes are removed, equals the municipal yield you keep tax-free.

Example:

• Municipal yield: 3.00%
• Federal tax rate: 24%
• State tax rate: 6%
• Combined rate: 30%

Calculation: TEY = 3.00% / (1 - 0.30) = 3.00% / 0.70 = 4.28%

This means a 4.28% taxable bond nets the same after-tax return as a 3.00% municipal bond for an investor in this tax bracket.

Federal Tax Brackets (2026)

Your federal marginal tax rate determines the municipal advantage. Higher brackets benefit more.

2026 Federal Income Tax Brackets (Married Filing Jointly)

Source: IRS, 2026 inflation adjustments (Notice issued October 2025).

The Net Investment Income Tax (NIIT)

High-income investors face an additional 3.8% Medicare surtax on investment income:

NIIT applies when:

• Modified AGI exceeds $250,000 (married filing jointly)
• Applies to interest, dividends, capital gains, and rental income

Critical point: Municipal bond interest is NOT subject to NIIT. This increases the effective tax advantage for high-income investors.

For top bracket investors:

• Taxable bond effective rate: 37% + 3.8% = 40.8%
• Municipal bonds exempt from both federal tax AND NIIT
• TEY = Muni Yield / (1 - 0.408)

State Tax Considerations (The In-State Advantage)

Most states exempt interest from bonds issued within that state. Out-of-state municipal bonds are typically subject to state income tax.

High-Tax States (Where State Exemption Matters Most)

In-State vs Out-of-State Calculation

Scenario: New York investor (6.85% state rate) in 37% federal bracket

In-state New York muni (triple tax-free):

• Combined rate: 37% + 6.85% + 3.8% NIIT = 47.65%
• TEY = 3.00% / (1 - 0.4765) = 5.73%

Out-of-state muni (state taxable):

• Only federal + NIIT avoided: 37% + 3.8% = 40.8%
• State tax still applies: 6.85%
• Net tax avoided: 40.8%
• TEY = 3.00% / (1 - 0.408) = 5.07%

The difference: In-state bonds provide an additional 0.66% tax-equivalent advantage for this investor.

Calculating Your Actual Tax Rate (The Details)

Getting the calculation right requires knowing your actual marginal rate, not just the bracket.

Step 1: Identify Your Federal Marginal Rate

Your marginal rate is what you pay on the next dollar of income, not your effective (average) rate.

Example:

• Taxable income: $400,000 (married filing jointly)
• Marginal bracket: 32%
• Add NIIT if applicable: 32% + 3.8% = 35.8%

Step 2: Add State Tax Rate (If Applicable)

For in-state munis: Add your state marginal rate if muni exemption is lost

For out-of-state munis: State taxes apply, reducing the benefit

California example:

• Federal: 37%
• State: 13.30%
• NIIT: 3.8%
• If in-state muni (triple exempt): Combined = 54.10%
• TEY = 3.00% / (1 - 0.541) = 6.54%

Step 3: Account for Phase-outs and Surtaxes

Some states have additional surtaxes on high incomes. Check your specific situation.

The AMT Complication (Private Activity Bonds)

Not all municipal bonds are fully tax-exempt. Private activity bonds may be subject to Alternative Minimum Tax.

What Triggers AMT

Private activity bonds (PABs) finance projects with significant private benefit:

• Airport terminal facilities
• Industrial development projects
• Multi-family housing bonds
• Student loan bonds
• Certain healthcare facilities

AMT treatment: PAB interest is included in AMT income calculation. For investors subject to AMT, these bonds lose part of their tax advantage.

AMT Yield Premium

AMT-subject bonds typically offer 5-20 basis points additional yield to compensate:

Example:

• Regular muni yield: 3.00%
• AMT-subject muni yield: 3.15%
• Premium: 15 basis points

Who should consider AMT bonds:

• Investors not subject to AMT
• Investors in the 10-12% brackets (rarely trigger AMT)
• High-yield seekers willing to accept AMT exposure

Who should avoid AMT bonds:

• High-income investors likely to trigger AMT
• Investors seeking maximum tax efficiency

Calculating TEY for AMT Bonds

If you’re subject to AMT, reduce the tax benefit accordingly:

AMT rates: 26% (up to $220,700 of AMTI) or 28% (above)

For AMT-subject investor:

• AMT bond yield: 3.15%
• If AMT rate is 28%, partial tax applies
• Effective yield reduced by AMT exposure
• Consult tax advisor for precise calculation

Muni-Treasury Ratios (Market Valuation Tool)

Professionals use the muni-Treasury ratio to assess relative value. This compares AAA muni yields to Treasury yields of similar maturity.

Current Ratios (early 2026)

Source: Tradeweb AAA muni curve vs. Treasury par curve, February 2026 snapshot. Ratios move daily—pull live data before acting on a relative-value view.

Interpreting Ratios

Below 80%: Munis expensive relative to Treasuries

• Explanation: Strong demand has compressed muni yields
• Implication: Less compelling value; be selective

80-90%: Historical fair value range

• Explanation: Normal relationship
• Implication: Standard analysis applies

Above 100%: Munis cheap relative to Treasuries

• Explanation: Typically occurs during stress (March 2020)
• Implication: Strong buy signal for appropriate investors

Why ratios matter: Even if your TEY calculation is favorable, you want to buy when munis offer good value relative to Treasuries.

Worked Examples (Full Calculations)

Example 1: Basic Federal Calculation

Investor profile:

• Federal marginal rate: 24%
• No state income tax (Texas resident)
• Income below NIIT threshold

Bond choice: Texas municipal bond yielding 3.50%

Calculation: TEY = 3.50% / (1 - 0.24) = 3.50% / 0.76 = 4.61%

Interpretation: A taxable bond must yield over 4.61% to beat this muni.

Example 2: High-Income with NIIT

Investor profile:

• Federal marginal rate: 37%
• NIIT applicable: 3.8%
• Florida resident (no state tax)

Bond choice: Florida municipal bond yielding 3.25%

Calculation: Combined rate = 37% + 3.8% = 40.8% TEY = 3.25% / (1 - 0.408) = 3.25% / 0.592 = 5.49%

Interpretation: A taxable bond must yield over 5.49% to beat this muni.

Example 3: California Triple-Tax-Free

Investor profile:

• Federal marginal rate: 37%
• California state rate: 13.30%
• NIIT applicable: 3.8%

Bond choice: California municipal bond yielding 2.90%

Calculation: Combined rate = 37% + 13.30% + 3.8% = 54.10% TEY = 2.90% / (1 - 0.541) = 2.90% / 0.459 = 6.32%

Interpretation: A taxable bond must yield over 6.32% to beat this California muni.

Example 4: Out-of-State Bond

Investor profile:

• Federal marginal rate: 32%
• New York state rate: 6.85%
• No NIIT

Bond choice: Texas municipal bond yielding 3.40% (out-of-state, state taxable)

Calculation: Only federal tax avoided = 32% TEY = 3.40% / (1 - 0.32) = 3.40% / 0.68 = 5.00%

Comparison: If equivalent NY muni yields 3.10%: NY TEY = 3.10% / (1 - 0.3885) = 3.10% / 0.6115 = 5.07%

Interpretation: The NY muni is slightly better despite lower stated yield.

Common Calculation Mistakes (And How to Avoid Them)

Mistake 1: Using Effective Rate Instead of Marginal

Wrong: “My average tax rate is 18%, so I’ll use that” Right: Use your marginal rate (rate on the next dollar of income)

The marginal rate determines the tax savings from municipal bonds.

Mistake 2: Forgetting State Taxes

Wrong: Only calculating federal benefit Right: Include state tax if muni exemption provides state savings

This is especially important in high-tax states like California and New York.

Mistake 3: Ignoring NIIT

Wrong: Using 37% as top rate Right: Adding 3.8% NIIT for high-income investors

Municipal bonds avoid NIIT; taxable bonds don’t.

Mistake 4: Assuming All Munis Are Tax-Free

Wrong: Treating all municipal bonds as equivalent Right: Checking for AMT exposure, state exemption status

Private activity bonds have different tax treatment.

Decision Framework (When Munis Make Sense)

Munis Clearly Advantageous

1. Federal bracket 32%+ (strong tax benefit)
2. High-tax state with in-state muni availability
3. NIIT applies (additional 3.8% saved)
4. Taxable account (tax advantages matter)

Munis Questionable

1. Federal bracket 22% or lower (limited tax benefit)
2. Tax-advantaged accounts (IRAs, 401(k)s - no benefit)
3. AMT-subject investor considering AMT bonds
4. Muni ratios below 70% (expensive relative to alternatives)

The Break-Even Question

Calculate your personal break-even:

1. Find your combined marginal rate (federal + state + NIIT if applicable)
2. Calculate TEY for available muni yields
3. Compare to available taxable yields at similar credit quality
4. Factor in muni-Treasury ratios for relative value

Investor Checklist

Essential Calculations

These 4 steps ensure accurate TEY comparison:

1. Identify your federal marginal bracket: Not effective rate, marginal rate
2. Add NIIT if applicable: Income over $250K (MFJ) adds 3.8%
3. Include state tax for in-state bonds: Full combined rate for triple-exempt
4. Reduce rate for out-of-state bonds: Only federal (and NIIT) avoided

High-Impact Considerations

For optimizing municipal bond decisions:

1. Check muni-Treasury ratios: Avoid buying when ratios are below 70%
2. Compare credit quality: TEY only valid at equivalent credit risk
3. Consider AMT status: Avoid PABs if you trigger AMT

Annual Review Items

Tax situations change; recalculate periodically:

1. Income changes affecting marginal bracket
2. State residency changes affecting state exemption
3. NIIT threshold changes
4. AMT exposure changes

Key Takeaways

1. TEY = Muni Yield / (1 - Tax Rate): Simple formula, significant implications
2. Marginal rate matters: Use your bracket rate, not average rate
3. NIIT adds 3.8% for high-income investors (munis avoid it)
4. In-state bonds provide additional state tax savings
5. AMT bonds require adjusted calculations; typically offer yield premium

Related Concepts

• Understanding Bond Insurance and Enhancements - Comparing insured vs. uninsured yields
• AMT-Subject Municipal Bonds - Deep dive into private activity bond taxation
• State-Specific Fund Strategies - Optimizing for in-state tax exemption

References

1. Internal Revenue Service. Revenue Procedure 2025-32, 2026 inflation adjustments for tax brackets, standard deduction, AMT exemption, and related provisions (October 2025).
2. Internal Revenue Service. Publication 550: Investment Income and Expenses (current edition).
3. Tax Foundation. State Individual Income Tax Rates and Brackets (current edition). https://taxfoundation.org/
4. SIFMA. US Municipal Bonds Statistics. https://www.sifma.org/research/statistics/us-municipal-bonds-statistics
5. Tradeweb. AAA Municipal Yield Curve. https://www.tradeweb.com/our-markets/institutional/rates/tradeweb-aaa-municipal-yield-curve/