When One Windfall Sends Two Premiums Higher
Picture a retired couple in their early 70s, both on Medicare, drawing around $190,000 a year from Social Security, a modest pension, and required IRA withdrawals. Their Part B premiums have felt manageable for years. Then one tax year they sell a rental property, convert a chunk of a traditional IRA to a Roth, or take a larger distribution than usual. Their joint modified adjusted gross income (MAGI) crosses $218,000. Two years later, both of their Medicare premiums jump at the same time.
That is IRMAA at work. The Income-Related Monthly Adjustment Amount (IRMAA) is the surcharge Medicare adds to Part B and Part D premiums for higher-income beneficiaries, calculated from the joint MAGI reported two years earlier. The rule that catches people off guard is simple: each spouse pays the full surcharge separately, with no split between them.
A recent retirement forum thread captured the sting. A couple converted $60,000 from a traditional IRA to a Roth in one year, feeling responsible about future tax planning. The following spring they discovered both of their Part B premiums had climbed by roughly $80 a month, for a full year. The conversion made sense on paper. The IRMAA bill was the surprise.
Why the Surcharge Hits Both Spouses in Full
Here is the math in plain terms. For 2026, a married couple filing jointly pays the standard $202.90 monthly Part B premium per person as long as MAGI stays at or below $218,000. Cross that line by a single dollar and each spouse’s premium jumps to $284.10, a surcharge of $81.20 per person per month. Because both spouses pay it, the household cost rises by nearly $2,000 a year for crossing the threshold by any amount.
The tiers keep climbing. Joint MAGI above $274,000 pushes each premium to $405.80. Above $342,000, it climbs to $527.50. At the top rung of $750,000 and above, each spouse pays $689.90 a month. That works out to well over $16,000 a year in Part B premiums for the household, before Part D surcharges layer on top.
The cliff structure matters more than the dollar amounts. IRMAA works as a cliff, not a gradual phase-in: one dollar over $218,000 and the full surcharge applies to both spouses for the entire year. A well-intentioned Roth conversion, a miscalculated required minimum distribution (RMD), or a large capital gain can quietly cost a couple thousands of dollars two years down the road.
How the Two-Year Lookback Changes the Playbook
Your 2026 Part B premium reflects the MAGI on your 2024 tax return. A windfall today shows up in premiums the year after next, often long after the trigger has been forgotten. Common culprits: selling a long-held home with gain above the $500,000 joint exclusion, an inherited IRA forcing large distributions, a business sale, or Roth conversions timed without a MAGI check.
The 2.8% Social Security cost-of-living adjustment (COLA) for 2026 does not shield anyone from IRMAA. The COLA raises the gross benefit, but the higher Part B premium comes straight out of the check. For a couple bumped up one tier, the surcharge can consume most of the raise.
The interaction that matters most is coordination. Many couples find it pays to convert smaller amounts across several years to stay under the next bracket. Others accept one deliberately high IRMAA year, converting aggressively once, then keeping income low afterward. Either approach beats stumbling across a threshold by accident.
Two Moves Worth Making Before You Cross a Line
Both moves cost nothing but attention, and both have to happen before the tax year ends.
- Project your MAGI for the current tax year before December, including all planned conversions, capital gains, and distributions. Know exactly where you stand relative to the $218,000, $274,000, and $342,000 lines. Trimming $2,000 off a Roth conversion can save nearly $2,000 in premiums two years later.
- If a life-changing event drove the income spike, such as retirement, a spouse’s death, divorce, or the loss of a pension, file Form SSA-44 with Social Security. The agency will reconsider your premium based on expected current income rather than the old return.
The hardest mistake to undo is a December Roth conversion done without checking the MAGI math. Once the calendar year closes, the window closes with it. Thresholds move slightly each year with inflation, and every household’s mix of income sources is different, so mapping the numbers with a tax preparer before pulling the trigger is time well spent.
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