Short answer: For IRMAA, tax-free does not mean IRMAA-free. Social Security generally defines Medicare MAGI as AGI + tax-exempt interest.
Why municipal bond interest counts
Tax-exempt interest may not be included in adjusted gross income, but Medicare adds it back when determining IRMAA MAGI. This can move someone closer to or across an IRMAA threshold without increasing ordinary taxable income by the same amount.
Municipal bonds can still serve a portfolio purpose. The important planning point is to compare their after-tax value while also accounting for possible Medicare premium effects.
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Sponsor this placementWhere to find tax-exempt interest
Tax-exempt interest is generally reported on Form 1040 even though it is not included in taxable income. Review the return used for the Medicare premium year rather than relying only on the taxable-income line.
The IRMAA MAGI checklist explains other items that commonly create confusion.
Example
Suppose AGI is $104,000 and tax-exempt municipal bond interest is $8,000. The Medicare MAGI estimate is $112,000 before other adjustments. That total, rather than AGI alone, is the number to compare with the applicable IRMAA thresholds.
Planning checklist
- Find AGI and tax-exempt interest on the relevant federal return.
- Add them before comparing the result with IRMAA brackets.
- Include planned Roth conversions, RMDs, gains, and other taxable events.
- Compare the investment's tax benefit with any possible Medicare premium increase.
- Recheck the estimate before a large bond purchase or year-end income decision.
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