IRMAA and MAGI: How Today’s Income Can Change Medicare Premiums

Put the tax year beside the premium year

IRMAA is not a separate income tax. It is an income-related monthly adjustment added to Medicare Part B and Part D costs for higher-income beneficiaries. The important timing detail is that Social Security generally looks back two years. A 2026 premium determination normally uses 2024 tax-return information, while income recognized in 2026 would generally appear in a 2028 premium determination.

That delay makes IRMAA easy to miss in a retirement projection. A useful planner should not merely show this year’s taxable income. It should map tax-year MAGI to the corresponding premium year, count how many household members are expected to be enrolled in Medicare then, and distinguish the base premium from the incremental IRMAA surcharge.

Planning takeaway

A tax decision and its Medicare effect usually appear on different calendar lines.

Identify what is moving MAGI

For IRMAA, modified adjusted gross income generally starts with adjusted gross income and adds tax-exempt interest. Traditional IRA or 401(k) distributions, Roth conversions, pensions, wages, taxable interest, dividends, and realized capital gains can therefore matter. Qualified Roth distributions generally do not increase federal AGI, but every transaction must still meet the applicable qualification rules.

Social Security is subtler. Up to 85% of benefits can be included in taxable income; that does not mean the benefit is taxed at an 85% rate. Other income changes provisional income, which can cause more of the benefit to become taxable and then flow into AGI. A planner should model that interaction instead of marking the entire benefit either taxable or tax-free.

• Ordinary-income driversWages, pensions, pre-tax withdrawals, and Roth conversions can increase AGI.
• Investment driversInterest, dividends, and realized gains may affect MAGI even when no retirement account is tapped.
• Benefit interactionAdditional income can cause a larger portion of Social Security to enter taxable income.

Treat a threshold as a price, not an automatic stop sign

IRMAA uses income tiers. Crossing a tier can increase monthly Part B and Part D charges, which gives the threshold a cliff-like effect. But a good decision compares the incremental premium with the lifetime benefit of the action that caused it. Avoiding a modest surcharge may not justify skipping a conversion that substantially reduces later RMDs, survivor taxes, or higher-bracket income.

For 2026, the first tier begins above $109,000 for a single filer and above $218,000 for married filing jointly. A married couple with two Medicare enrollees just into that first tier faces about $2,297 of combined annual Part B and Part D surcharges, based on the published monthly additions. That is meaningful, but it is not automatically a $5,000 or $10,000 penalty and should not be described that way.

Know when current income may replace an old return

A two-year-old return may reflect income that no longer represents the household. Social Security provides Form SSA-44 for certain life-changing events, including work stoppage or work reduction, when a beneficiary asks for a lower IRMAA determination. Retirement can therefore be relevant, but eligibility, evidence, timing, and the exact event must be verified.

Use the Medicare timeline as an early-warning system. Flag years near a threshold, show the modeled income drivers, and preserve the difference between an estimate and a notice from Social Security. Before acting on conversions, gains, or an appeal, coordinate the retirement projection with an actual tax projection and current official instructions.