One Roth Conversion at 63 Can Spike Your Medicare Premium Two Years Later. Here’s the Cliff.
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A 63-year-old couple converts $90,000 from a traditional IRA to a Roth in 2026, expecting clean tax-free growth and a smaller required minimum distribution down the road. Their accountant signs off on the tax bill. Two years later, the Social Security Administration sends a letter saying their 2028 Medicare Part B premium will be higher than the standard amount, and their Part D plan will carry an extra surcharge on top. Nobody warned them, because the conversion happened before Medicare enrollment ever entered the picture.
This article is for the small slice of pre-enrollees whose taxable income, combined with a planned conversion, could push their modified adjusted gross income above an IRMAA threshold. CMS says income-related Part B adjustments affect about 8% of people with Medicare Part B. If your joint MAGI in the conversion year will sit well below the current first threshold of $218,000, or $109,000 for single filers, IRMAA may not be an immediate concern. For everyone else approaching 65, the next few sections explain whether a conversion saves money or quietly costs it.
IRMAA generally uses the tax return from two years prior. A conversion completed in 2026 lands on the 2026 Form 1040, which generally sets 2028 Part B and Part D premiums. Turning 65 in 2028 can mean your first Medicare premium is already shaped by a decision you made at 63. MAGI for IRMAA equals adjusted gross income from Form 1040, line 11, plus tax-exempt interest from line 2a. Municipal bond income that feels tax-free still counts, and the taxable amount of a Roth conversion flows through AGI.
The Cliff: One Dollar Triggers the Whole Surcharge
IRMAA works as a cliff. Cross a threshold by a single dollar and you pay the full tier surcharge for the entire year, per person. Here are selected 2026 brackets for joint filers with full Part B coverage:
| Joint MAGI (per person, monthly) | Part B surcharge | Total Part B premium |
|---|---|---|
| ≤ $218,000 | $0.00 | $202.90 |
| $218,001 – $274,000 | $81.20 | $284.10 |
| $274,001 – $342,000 | $202.90 | $405.80 |
| ≥ $750,000 | $487.00 | $689.90 |
Picture a couple with $215,000 in baseline MAGI doing a $60,000 taxable conversion. They land at $275,000, one thousand dollars into the second IRMAA surcharge tier. The Part B surcharge is $202.90 per person per month, and the Part D surcharge in that tier is $37.50 per person per month. Across both spouses for a full year, that tier costs $5,769.60 in surcharges. Trim the conversion enough to stay at $274,000 or below, and the surcharge drops to the first tier instead.
SSA-44 Will Not Save You
Readers often assume they can appeal. Form SSA-44 applies only when income fell because of a qualifying life-changing event: marriage, divorce or annulment, death of a spouse, work stoppage, work reduction, loss of pension income, loss of income-producing property, or certain employer settlement payments. A voluntary Roth conversion is not on that list. Neither is a voluntary home sale or a large RMD. The cliff you walked over at 63 generally remains in place for the premium year it touches.
Convert Before the Lookback Window, Then Ladder
The pre-enrollment window is the cleanest conversion runway many retirees get. For someone first enrolling in Medicare in 2028, conversions completed in 2025 generally would not affect a Medicare premium because the 2025 return would drive 2027 premiums, before enrollment. Conversions in 2026 can hit the first Medicare year. A laddered approach, with smaller conversions spread across multiple years and sized below the next bracket, can preserve Roth benefits without triggering an avoidable cliff.
Survivors face an underreported version of the same trap. A surviving spouse may still be able to file jointly for the year of death, but many older survivors eventually file as single, and the single IRMAA brackets are roughly half the joint ones. Income often falls after a death, but not always by half. The bracket can shift faster than the household budget does.
What to Do Before December 31
- Model your projected MAGI, which is AGI plus tax-exempt interest, for every year between now and Medicare enrollment, and identify which conversion year drives which Medicare premium year using the two-year lookback.
- Size each conversion to land at least a few thousand dollars below the relevant IRMAA threshold for your filing status.
- If a qualifying life-changing event, such as work stoppage, death of a spouse, or divorce, cuts your income after the lookback locks, file Form SSA-44 promptly with documentation. It will not unwind a voluntary conversion, but it may reduce the premium hit from a qualifying income drop.
The Conversion Can Still Be Worth It
A Roth conversion before Medicare can still be smart. The mistake is measuring only the income-tax bill and ignoring the premium year the conversion may shape. Before December 31, retirees approaching 65 should run the tax savings and the IRMAA cliff in the same calculation, then convert only the amount that still makes sense after both bills are counted.
Source note: 2026 Medicare premium and IRMAA figures are from the CMS fact sheet released November 14, 2025. SSA-44 qualifying-event rules and the IRMAA reduction process are from Social Security Administration guidance. Article uses 2026 plan-year rules as a planning reference.
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