A 72-year-old couple in Ohio asked their advisor whether to convert $50,000 from a traditional IRA to a Roth before year-end. Their combined income from Social Security, a small pension, and required minimum distributions already puts them around $210,000 in modified adjusted gross income, just under the first IRMAA cliff. The conversion would lift them across it. The question is what that crossing actually costs.
This article is for the small slice of Medicare households inside that danger zone. Roughly 8% of Part B beneficiaries pay any income-related surcharge at all. If your joint MAGI sits comfortably below $218,000 (or $109,000 single), a Roth conversion will not trip an IRMAA bill. Stop reading and convert away. For everyone else within $50,000 of a bracket, the math below is the math that matters.
What MAGI Actually Counts
For IRMAA, modified adjusted gross income is Form 1040 line 11 plus tax-exempt interest from line 2a. Municipal bond income that feels tax-free still counts. A Roth conversion shows up dollar-for-dollar in AGI the year you do it, so a $50,000 conversion raises MAGI by $50,000. The Social Security Administration then looks at that MAGI two years later: 2026 conversions drive 2028 Medicare premiums.
The Cascade, in Three Layers
A conversion at this income level stacks three taxes on the same dollars.
Layer 1: Ordinary federal tax. The couple sits in the 24% bracket for joint filers earning between $206,700 and $394,600 in 2026. The conversion adds approximately $12,000 in federal tax. State income tax in Ohio adds roughly another $1,750.
Layer 2: Social Security already maxed. At this income, 85% of their Social Security benefit is already taxable, the statutory ceiling. The conversion does not push more benefit into income because there is no more room to push. For lower-income retirees this layer can sting; here it is silent.
Layer 3: The IRMAA jump. The IRMAA jump. The pre-conversion MAGI of $210,000 sat below the first joint threshold. The post-conversion MAGI of $260,000 lands in the $218,000 to $274,000 tier. For 2026 that tier carries a Part B surcharge of $81.20 per person per month and a Part D surcharge of $14.50 per person per month. For a couple, that is $191.40 a month, or about $2,297 per year during the year the surcharge applies.
The Total, on One Basis
Every figure below is a one-time cost triggered by this single $50,000 conversion, paid by the couple, in dollars.
| Cost component | Dollars |
|---|---|
| Federal income tax at 24% | $12,000 |
| Ohio state income tax (approx. 3.5%) | $1,750 |
| Part B + Part D IRMAA, both spouses, one year | $2,297 |
| Total cost of the conversion | $16,047 |
That is an effective rate of roughly 32% on the converted dollars. Move the same couple closer to the next cliff, add a higher-tax state, or convert into the 32% federal bracket, and the stack runs 38% to 45%. The headline rate is scenario-specific. The mechanic is not.
The Reset, and What SSA-44 Won’t Do
The IRMAA surcharge from a one-time conversion generally affects one premium year if income returns to baseline. If the conversion occurs in 2026, it affects premiums based on the 2026 tax year under Medicare’s two-year lookback. When income later returns to baseline, future premiums are recalculated using the lower income year.
The unmerciful part: do not file SSA-44 expecting relief. The form reverses IRMAA only after a qualifying life-changing event, marriage, divorce, death of a spouse, work stoppage, work reduction, loss of an income-producing property, loss of pension income, or an employer settlement. A voluntary Roth conversion is none of these. The SSA will deny the request.
One more trap worth flagging: when one spouse dies, the survivor files single. The single IRMAA thresholds start at $109,000, roughly half the joint figure. The same household income that paid no surcharge as a couple can land two tiers up as a survivor. Plan conversions with that horizon in mind.
What to Do
- Pull your most recent 1040. Add line 11 and line 2a. Compare that MAGI to the $218,000 joint / $109,000 single first thresholds for 2026. The gap between your number and that line is your conversion headroom for this year without triggering IRMAA.
- If a planned conversion exceeds that headroom, split it across two or three tax years. Smaller annual chunks can stay under the cliff entirely, or cross only one tier instead of two.
- If your combined household income is within $20,000 of a bracket, a fee-only advisor who models Medicare-aware withdrawal sequencing can usually identify whether the conversion clears the math after IRMAA, state tax, and the survivor scenario are all priced in.
Source note: 2026 plan-year figures from the CMS fact sheet on 2026 Medicare Parts A & B Premiums and Deductibles and the IRS 2026 inflation adjustments.
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