A Roth conversion can look like a clean win: pay tax now, skip required minimum distributions later, and leave heirs a tax-free account. For many adults 50 and up, that pitch is irresistible — especially if you’re staring down RMDs under SECURE 2.0. The trap is quieter. Convert too much in the wrong year, and you can trigger IRMAA — Medicare’s income-related monthly adjustment amount — and pay higher Part B and Part D premiums for a full calendar year.
The Roth conversion IRMAA Medicare trap isn’t about “bad” conversions. It’s about timing, cliffs, and a two-year lookback most people don’t map until the Social Security notice arrives.
How a Roth conversion works — and why taxes hit this year
A Roth conversion moves money from a traditional IRA or 401(k) into a Roth IRA. You generally owe ordinary income tax on the converted amount in the year of the conversion. Once the money is in the Roth, qualified withdrawals can be tax-free, and Roth IRAs have no RMDs for the original owner.
That last point is why converters rush. Under SECURE 2.0, RMDs generally start at age 73 if you were born from 1951 through 1959, and at age 75 if you were born in 1960 or later. Shrinking a traditional balance before those ages can reduce future forced withdrawals. What often gets skipped: the conversion itself raises modified adjusted gross income (MAGI) in the conversion year — and Medicare cares about MAGI two years later.
What is IRMAA and how does the two-year lookback work?
IRMAA is an extra amount some Medicare enrollees pay on top of standard Part B and Part D premiums when MAGI from two years earlier crosses set thresholds. For 2026 premiums, Social Security and CMS look at your 2024 MAGI. Convert heavily in 2024, and 2026 premiums can jump — even if your cash income that year is modest.
For 2026, the standard Medicare Part B premium is $202.90 a month if your MAGI stays at or below the first threshold: $109,000 for single filers and $218,000 for married couples filing jointly. Cross those lines by even a dollar, and you don’t pay a little more — you land in the next IRMAA tier for the year.
2026 IRMAA cliffs: Part B and Part D examples
CMS publishes the surcharge tiers each year. In plain language for 2026:
- MAGI at or below $109,000 (single) / $218,000 (joint): standard Part B of $202.90; no Part D IRMAA add-on.
- Next tier (just over those amounts, up to $137,000 single / $274,000 joint): Part B total $284.10 a month (standard plus an $81.20 surcharge); Part D IRMAA add-on of $14.50 on top of your plan premium.
- Higher tiers climb from there, with Part B totals up to $689.90 a month at the top bracket, plus larger Part D add-ons.
IRMAA is a cliff, not a smooth ramp. One dollar over a threshold can cost you the full surcharge for that tier for the entire year — on Part B, Part D, or both.
Why you can’t undo a Roth conversion anymore
Before the Tax Cuts and Jobs Act, you could sometimes “recharacterize” a Roth conversion — effectively reverse it if markets fell or you realized you’d overshot. That option is gone for conversions. Once you convert, the tax bill and the MAGI impact generally stick. That permanence makes IRMAA planning more important, not less. You can’t convert, see the Medicare notice two years later, and rewind the transaction.
Can Form SSA-44 fix an IRMAA spike from a conversion?
If your income drops because of certain life-changing events, you may be able to ask Social Security for a new initial determination using Form SSA-44. Qualifying events are specific (think things like work stoppage, divorce, or death of a spouse — the form lists the categories Social Security recognizes).
A Roth conversion itself is not a qualifying life-changing event for that purpose. Converting raised your MAGI on purpose. SSA-44 is for situations where a recognized event reduced your income after the tax year Medicare is using — not for unwinding elective conversions. Don’t count on the form as a backdoor undo button.
The “trough year” window — and the age 63–64 trap
Many advisors talk about trough years: the stretch after you leave W-2 work and before RMDs begin. Taxable income often dips. Those years can be useful for filling lower tax brackets with Roth conversions.
Medicare’s lookback adds a twist. Conversions at 63 or 64 can affect premiums when you go on Medicare at 65 or 66. You’re not “safe” just because you’re not on Medicare yet. The conversion year’s MAGI still feeds the IRMAA calculation two years later.
So the trough can still help — if you size conversions against the IRMAA thresholds that will apply when those two years catch up, not just against this year’s tax bracket.
How to size Roth conversions smarter around IRMAA in 2026
You don’t need a complex model. You need a simple checklist before you convert:
- Project MAGI for the conversion year, including Social Security taxation, capital gains, and the conversion itself.
- Map that MAGI to the IRMAA brackets that will apply two years later (for money converted in 2024, that’s 2026 premiums; for conversions in 2026, think 2028).
- Stop short of the next cliff if the extra surcharge would wipe out the near-term benefit of converting that last chunk.
- Remember couples: joint thresholds are higher, but both spouses can face Part B and Part D IRMAA when MAGI crosses the line.
- Spread large conversions across multiple years instead of one “fill the bracket” blowout that leaps a cliff.
Hypothetical illustration (not a prediction): Suppose you’re single in a year that will set 2026 Medicare premiums. Your MAGI without a conversion sits at $108,500 — under the $109,000 first threshold. Convert $2,000 more and you clear $109,000. Under 2026 rules, that move can take you from the $202.90 standard Part B premium to the $284.10 tier ($81.20 more per month), plus a $14.50 Part D IRMAA add-on if you have Part D. Roughly $95.70 a month combined, or about $1,148 for the year — triggered by crossing a cliff by a small amount. Your actual tax on the conversion and your Part D plan premium will differ; the point is the cliff math, not a promised savings figure.
Roth conversions vs. RMD avoidance: the contrarian take
Avoiding future RMDs is a real goal. It is not automatically worth an IRMAA hit for a full year — especially if you’re already near a threshold, newly on Medicare, or both spouses will pay surcharges. Sometimes a smaller conversion (or waiting a year) preserves more cash than a larger conversion that “beats” RMDs on paper.
Also weigh what else is in MAGI: capital gains from downsizing, taxable Social Security, pensions, and side income stack with conversions. The conversion isn’t judged alone; the whole MAGI pile is.
What to do before you convert this year
Run the numbers with the official CMS IRMAA table for the premium year you’re affecting. Confirm your filing status thresholds. If you’ve already converted and your income later fell for a qualifying life-changing event, look at SSA-44 — knowing a conversion alone won’t qualify. If you’re in a trough year at 63–64, treat Medicare premiums at 65–66 as part of the conversion cost, not an afterthought.
Roth conversions remain a powerful tool. The IRMAA trap is simply this: Medicare’s two-year lookback can turn a tax-smart move into a year of higher Part B and Part D bills if you ignore the cliffs. Size the conversion to the brackets you’ll live with two years from now — not just the RMD age you’re trying to soften.
