A Roth conversion is taxable income, so it raises your MAGI and can push you into a higher IRMAA bracket. Because IRMAA looks back two years, the timing of your conversions is what keeps the surcharge in check.
When you convert money from a Traditional IRA or 401(k) into a Roth, you move pre-tax dollars into an account where they will grow tax-free. The catch is that the amount you convert is fully taxable in the year you convert it. That pre-tax money was never taxed going in, so the IRS taxes it on the way over.
The taxable amount of the conversion lands in your adjusted gross income, and that flows straight into your MAGI. IRMAA brackets are measured against your MAGI, so a large conversion can lift your income past a threshold even when nothing else about your finances changed. To see exactly what feeds into that number, read what counts as MAGI.
It helps to separate two things people often blur together. The conversion itself is taxable and counts. A later withdrawal from the Roth is not. So the income hit happens once, in the year you convert, and never again on that money. The planning question is simply how much to convert in any given year and which years to do it in.
Social Security does not set your IRMAA from this year's income. It uses the most recent tax return on file, which runs two years behind. So a conversion you make this year shows up in the MAGI that drives your Medicare premium two years later. A 2026 conversion, for example, can affect your 2028 premium.
This gap is the whole reason timing matters. The year you convert is not the year you feel the surcharge, so you plan around the return that will set the premium. For the full mechanics of the delay, read the IRMAA 2-year lookback explainer.
Many people have a window where their income drops for a few years. It often opens after you stop working and closes when required minimum distributions (RMDs) begin and Medicare starts. During that stretch your MAGI may be the lowest it will ever be, with no wages, no RMDs, and few other large sources of income.
Those years are the natural place to convert. With your baseline income low, you can move a meaningful amount into a Roth and still stay under an IRMAA threshold. Converting before Medicare begins also means the early years of a conversion plan may never touch a Medicare premium at all, because there is no premium yet to surcharge.
The goal is not to avoid converting. It is to convert without spilling over the next IRMAA line. Each bracket is a cliff: one dollar above a threshold adds the full surcharge for the year, not a small fraction of it. So the smart move is to convert only up to just under the next threshold and stop there.
That takes a number, not a guess. Start with your expected MAGI for the year, then see how much headroom you have before the next bracket. The calculator shows that distance, so you can size each conversion to fill the room without crossing the line. If you want a deeper walkthrough of staying just under, see how to avoid the IRMAA cliff.
Spreading conversions across several years is often the cleaner path than one large conversion. Smaller annual amounts let you top up to the same threshold year after year, which can move a sizable balance over time while keeping each single year under the line. Remember to leave room for the rest of your income too, since dividends, interest, and any other taxable amounts share the same MAGI as your conversion.
Sometimes the math points the other way. A large Traditional balance left alone keeps growing, and once RMDs begin they can force out big taxable withdrawals every year, pushing your MAGI up and your IRMAA with it for the rest of your life. Converting now shrinks that future balance, which can lower your RMD-driven MAGI for years to come.
In that case a single year of higher IRMAA may be a price worth paying. You accept one surcharge bump now in exchange for lower premiums and lower taxes across many later years. The right answer depends on your balances, your tax rate, and how long the savings have to compound, which is exactly the kind of tradeoff worth modeling before you act.
You may be able to reduce your surcharge by appealing with Form SSA-44.
Source: IRS Roth conversion rules; SSA IRMAA rules (publication 05-10536). Informational only, not financial or tax advice. Last verified June 2026.