Retiree With $1.2 Million Discovers Roth Conversion Doubled His First Medicare Premium

A man turns 65, enrolls in Medicare, and opens his first premium notice expecting the standard rate. Instead, the number is roughly double. He did nothing wrong that year. The damage was done two years earlier, at age 63, when his advisor walked him through a Roth conversion designed to fill the 24% bracket before required minimum distributions became an issue. The conversion was mathematically sound. The retiree and advisor simply never ran the Medicare numbers alongside the tax numbers.

Medicare’s Income-Related Monthly Adjustment Amount, known as IRMAA, uses modified adjusted gross income from two years prior to set the current year’s Part B and Part D surcharges. Enroll at 65, and Social Security pulls the tax return from age 63. That is precisely the age at which many pre-retirees run their largest conversions: they are no longer working, have not yet claimed Social Security, and want to move money out of traditional IRAs before RMDs begin.

A $180,000 conversion stacked on top of even modest interest, dividends, or part-time income easily pushes a single filer past the second IRMAA cliff. Because IRMAA operates as a pure cliff system, one dollar over a threshold triggers the full surcharge for the entire tier.

For 2026, the standard Part B premium is $202.90 per month. The tiers for a single filer, based on 2024 MAGI, are:

1. MAGI at or below $109,000: standard premium of $202.90, no surcharge.
2. MAGI between $109,000 and $137,000: total premium of $284.10.
3. MAGI between $137,000 and $171,000: total premium of $405.80.
4. MAGI between $171,000 and $205,000: total premium of $527.50.
5. MAGI between $205,000 and $500,000: total premium of $649.20.
6. MAGI above $500,000: total premium of $689.90.

A $180,000 conversion added to a few thousand in taxable interest lands comfortably in the third tier. The combined full-year surcharge on Part B and the parallel Part D surcharge comes to several thousand dollars for a single filer. At the top tier, a beneficiary pays $689.90 per month for Part B alone, which is more than triple the standard premium and exceeds $8,200 per year.

The Social Security Administration does allow appeals through Form SSA-44 for eight defined life-changing events: marriage, divorce or annulment, death of a spouse, work stoppage, work reduction, loss of income-producing property, loss of pension income, and an employer settlement payment. A Roth conversion appears on none of those eight. SSA Program Operations Manual System (POMS) section HI 01120.005 expressly excludes IRA conversions, capital gains, and similar voluntary income spikes from qualifying events, so the surcharge simply has to be paid.

The Fix He Wishes He Had Known

Two strategies would have prevented this outcome.

The stronger path is to finish large conversions by the year you turn 62. Conversion income from that year and earlier never affects IRMAA because the two-year lookback window sits entirely before Medicare eligibility. For someone with a $1.2 million portfolio and a multi-year conversion plan, this alone can move six figures of taxable IRA money into a Roth without any surcharge exposure.

The secondary path is to size each conversion to stop just under an IRMAA threshold from age 63 onward. Treat the $109,000 and $137,000 single-filer lines as hard ceilings that override bracket-based conversion sizing. The federal 24% bracket for a single filer in 2026 runs to $201,775, which is why bracket-focused advice so routinely blows past IRMAA cliffs. The Medicare cliff sits well below the top of the 24% bracket, and the One Big Beautiful Bill Act signed in July 2025 made that bracket structure permanent, so the mismatch between bracket limits and IRMAA thresholds is not going away.

One additional wrinkle worth noting: the OBBBA also added a new $6,000 senior standard deduction for filers aged 65 and older, which phases out at $75,000 of MAGI for single filers. That deduction reduces taxable income but does not reduce MAGI, so it does nothing to lower an IRMAA surcharge. Retirees who count on the senior deduction to offset a large conversion year will still face the full cliff if their MAGI crosses a threshold.

Converting anyway can still be correct. When avoiding a future RMD taxed at 32% or 35% is on the table, a one-year surcharge measured in the low four figures may be worth accepting. The point is to know the cost before signing the paperwork, not to discover it when the Medicare notice arrives.

What to Do This Year

Anyone between 60 and 64 with a seven-figure traditional IRA should pull two numbers before scheduling another conversion: projected MAGI for the current year, and the IRMAA threshold immediately above it. If the conversion crosses a threshold, price the surcharge explicitly and decide whether the long-term Roth benefit justifies the cost. Running both calculations side by side, tax bracket and IRMAA exposure, takes a few minutes and can prevent the kind of surprise this retiree encountered when he opened his first premium notice.

Editor’s note: This article was updated to add the missing sixth IRMAA tier for single filers with 2024 MAGI above $500,000 (total Part B premium of $689.90 per month), to expand the SSA Form SSA-44 qualifying events list to the full eight events defined by POMS HI 01120.005 (including its express exclusion of IRA conversions), and to add context on the One Big Beautiful Bill Act’s permanence of tax brackets and new senior standard deduction as they relate to IRMAA planning.

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