Quick Answer

IRMAA uses modified adjusted gross income, generally adjusted gross income plus tax-exempt interest. For 2026 Medicare premiums, SSA says it uses the most recent federal tax return provided by the IRS, which is often the return from two years earlier.

What Is IRMAA MAGI?

For Medicare premium purposes, MAGI is not always the same number people use for other tax planning rules. A practical planning estimate is:

IRMAA MAGI = adjusted gross income + tax-exempt interest.

That means municipal bond interest can matter for IRMAA even if it is not regular taxable income. Roth conversions, traditional IRA withdrawals, capital gains, pensions, wages, dividends, and taxable Social Security can also affect the number.

The Two-Year Lookback

The lookback rule is the timing issue. A 2026 premium determination usually relies on income from an earlier tax return. If a household had unusually high income two years ago, it may receive an IRMAA notice even if current income is lower.

This is common around retirement. A person may work full-time in one year, retire the next year, and then be surprised when Medicare premiums still reflect the earlier working income.

What If Income Has Gone Down?

SSA provides a process for asking for a new determination when income goes down because of certain life-changing events. Examples can include work stoppage, work reduction, marriage, divorce, annulment, death of a spouse, loss of income-producing property, loss of pension income, or employer settlement payment changes.

The form commonly associated with this process is SSA-44. Not every income drop qualifies, and proof may be needed, so it is important to read the official SSA instructions or speak with SSA directly.

How To Plan With The Lookback

  • Think two years ahead when making large conversions or gains.
  • Track MAGI, not just taxable income.
  • Model married and single filing status if one spouse may outlive the other.
  • Keep documentation if a qualifying life-changing event reduces income.

Planning Example

A taxpayer completes a large Roth conversion in 2026. That conversion may not affect the 2026 premium because the 2026 premium is tied to prior income data. But it may influence a future premium year when the 2026 return is used. This is why Roth conversion planning should include both the tax return year and the later Medicare premium year.

Next step: Use current 2026 tiers as a planning proxy while remembering that future IRMAA brackets may change.

Estimate IRMAA MAGI

Sources