How to Calculate Your IRMAA MAGI From Your Tax Return
The letter from Social Security arrives, and your Medicare premiums just went up. The reason is a number you already filed: your MAGI from two years ago. Grab that return. The whole calculation is two lines and one addition, and once you can do it yourself, you can plan around it instead of being surprised by it.
The Two-Line Formula
IRMAA's MAGI (Modified Adjusted Gross Income) is refreshingly simple compared to most tax math:
| Step | Line | What to take |
|---|---|---|
| 1 | Form 1040, Line 11 | Your adjusted gross income (AGI) |
| 2 | Form 1040, Line 2a | Your tax-exempt interest |
| 3 | Form 2555 (if you filed it) | Foreign earned income you excluded |
Add the three numbers. That is your IRMAA MAGI. Most people only have the first two; skip step 3 if you never filed Form 2555.
The trap is line 2a. Tax-exempt interest, usually from municipal bonds, does not appear on your tax bill, so it feels like it should not count. But Medicare adds it back. This is the line that catches retirees with modest AGIs and big muni holdings: their MAGI is higher than their taxable income, and they land in an IRMAA bracket they never saw coming.
Which Return Counts (the Two-Year Lookback)
For your 2026 premiums, Social Security looks at your 2024 tax return. That timing gap is what makes IRMAA sting: a one-time event in 2024, a big Roth conversion, a large IRA withdrawal, selling investments, selling a property, can raise your 2026 premiums even though your income has long since settled back down. The surcharge lasts for the premium year, then recalculates from the next return.
One nuance worth knowing: if your 2024 return is not processed yet when SSA makes the initial determination, they may temporarily use 2023 and update later. And if your income dropped because of a life-changing event, retirement, marriage, divorce, death of a spouse, you can file Form SSA-44 to ask for a recalculation. I covered that process in How to Appeal IRMAA With Form SSA-44.
What Counts and What Does Not
Since MAGI starts with AGI, nearly everything taxable lands in it: wages, taxable Social Security benefits, traditional IRA and 401(k) withdrawals, capital gains, pension income, and rental income. Qualified Roth withdrawals generally stay out, which is why Roth money is the favorite IRMAA-planning tool. Tax-exempt interest is the odd one out: untaxed, but counted anyway.
The planning implication is blunt. If you are near a bracket edge, the income sources you control, IRA withdrawal timing, Roth conversion size, muni holdings, are the ones to manage. I wrote a deeper guide to the income that feeds the calculation in What Income Counts Toward IRMAA MAGI. And our IRMAA calculator will take your MAGI and filing status and tell you exactly which tier you land in.
Frequently Asked Questions
How do I calculate my MAGI for IRMAA?
Add three numbers from your tax return: your AGI from Form 1040 Line 11, your tax-exempt interest from Line 2a, and any foreign earned income exclusion from Form 2555. That total is the MAGI the Social Security Administration uses for IRMAA.
Which tax year does 2026 IRMAA use?
2026 IRMAA is based on your 2024 tax return. Medicare uses a two-year lookback, so a one-time income event in 2024, like a large Roth conversion or a home sale, can raise your 2026 premiums even if your current income is lower.
Does tax-exempt municipal bond interest count toward IRMAA?
Yes. Even though municipal bond interest is exempt from federal income tax, Medicare adds it back to your AGI when calculating IRMAA MAGI. It comes from Line 2a of Form 1040.
Do Roth IRA withdrawals count toward IRMAA MAGI?
Qualified Roth IRA withdrawals generally are not included in AGI, so they usually do not raise your IRMAA MAGI. Withdrawals from traditional IRAs and 401(k)s are different: those count as taxable income and feed into MAGI.
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