Quick Read
Social Security uses a two-year lookback, meaning your 2025 tax return determines your 2027 Medicare IRMAA surcharges announced each November.
IRMAA MAGI adds tax-exempt municipal bond interest (Line 2a) to AGI (Line 11), and Roth conversions flow directly into that total.
A spouse’s death cuts the joint IRMAA threshold from $218,000 to $109,000, potentially triggering large surcharges even if income barely changed.
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The November Letter That Already Has Your Name On It
A retired couple in Naples converted $95,000 from a traditional individual retirement account to a Roth IRA in October 2025. They wanted to shrink future required minimum distributions (RMDs) and liked the idea of paying tax while they could control the timing. Their usual modified adjusted gross income was approximately $190,000. The conversion pushed it near $285,000.
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When the couple filed their return in April 2026, that income number became permanent. What it will cost them in Medicare premiums remains unfinished. The Centers for Medicare and Medicaid Services typically publishes the following year’s premiums and income brackets in November. Social Security then uses the couple’s 2025 tax information to calculate their 2027 income-related monthly adjustment amount (IRMAA).
Half the letter is already written. November supplies the price.
Medicare Looks Back Two Years
The IRMAA raises Medicare Part B and Part D costs for higher-income beneficiaries. Social Security generally uses tax information from two years earlier, which means:
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A 2024 return determines 2026 premiums.
A 2025 return determines 2027 premiums.
A 2026 return will determine 2028 premiums.
The 2027 thresholds and premium amounts have not yet been announced. The 2026 figures can provide a warning, but they cannot tell anyone exactly what the 2027 bill will be. For reference, the first 2026 surcharge begins when modified adjusted gross income (MAGI) exceeds $109,000 for most individual filers or $218,000 for married couples filing jointly. The first tier adds $81.20 a month to the standard Part B premium and $14.50 to Part D, per person. At the top, a married couple can pay thousands of dollars in annual surcharges. The 2027 dollar amounts may change, but the two-year lookback does not.
Line 11 Is Almost the Answer
For IRMAA, MAGI generally equals adjusted gross income (AGI) from Line 11 of Form 1040 plus tax-exempt interest from Line 2a. That second line catches people. Municipal bond interest may be exempt from federal income tax, but Medicare still includes it when measuring income for premium purposes.
Suppose a couple reports $210,000 on Line 11 and $12,000 of tax-exempt interest on Line 2a. Their MAGI is $222,000, not $210,000. Under the 2026 thresholds, that would cross the first joint-filer line. Whether it crosses the 2027 line will not be known until the new schedule arrives. The Roth conversion is less subtle. Its taxable portion flows into adjusted gross income, lands on Line 11, and remains there when the Internal Revenue Service sends the return information to Social Security.
Widowhood Can Move the Line Overnight
IRMAA becomes especially painful after one spouse dies. In 2026, the first surcharge begins above $218,000 for a married couple filing jointly but above only $109,000 for most single filers. Consider a couple with MAGI of $210,000. Filing jointly, they remain below the 2026 starting line. If one spouse dies and the survivor’s MAGI remains around $210,000, the survivor lands deep in the single-filer brackets. The income may have changed little. The amount of room beneath the surcharge has been cut in half.
The death of a spouse is a qualifying event for an IRMAA appeal. That does not guarantee relief. Social Security will consider the survivor’s lower projected income, and if it remains above the applicable threshold, the surcharge can continue.
Form SSA-44 Has a Short Guest List
Form SSA-44 allows someone to request a new IRMAA determination after certain life-changing events reduce household income. Those events include marriage, divorce, the death of a spouse, stopping or reducing work, losing pension income, losing income-producing property under qualifying circumstances, or receiving an employer settlement payment.
A voluntary Roth conversion is not on that list. Neither is choosing to sell a home or taking a large required minimum distribution. If the Naples couple has no separate qualifying event and the tax return is accurate, the conversion alone does not give them grounds to replace the 2025 income figure. An amended tax return is different. If the original return contained an error and the Internal Revenue Service accepts a correction, Social Security can reconsider the premium using the amended information.
What Can Still Be Done Before November
The 2025 return cannot be rewritten for planning purposes, but it can still reveal what may be coming:
Add Line 11 and Line 2a. Compare the total with the 2026 brackets as an early warning, leaving room for the 2027 thresholds to change.
Identify any qualifying life event. If marriage, divorce, widowhood, retirement, reduced work, or pension loss lowered current income, gather the documents needed for Form SSA-44.
Start budgeting for the surcharge. Someone well above the current bracket lines should not wait for the November letter to acknowledge that higher 2027 premiums are likely.
Protect 2028 while there is still time. Income realized before December 31, 2026, will generally shape the 2028 Medicare bill. Model Roth conversions, capital gains, and large retirement-account withdrawals with that delayed cost included.
November will reveal what the 2025 return costs. It will not change what the return says. The Medicare premium still open to negotiation is the one tied to income being created now.
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