Under the two-year lookback rule, the Modified Adjusted Gross Income (MAGI) from the 2025 tax return (Line 11 AGI plus tax-exempt municipal bond interest from Line 2a) will be used to calculate the income-related monthly adjustment amount (IRMAA) for 2027 Medicare Part B and Part D. Roth conversions also flow into this total. The Centers for Medicare and Medicaid Services typically publishes the following year's premiums and income brackets each November.