Roth Conversions Without Triggering IRMAA

How do you convert to a Roth without accidentally jacking up your Medicare bill? You convert up to the IRMAA line and not a dollar past it. IRMAA, the income-related monthly adjustment amount, is a surcharge added to your Medicare Part B and Part D premiums once your income clears a set of thresholds. A Roth conversion is ordinary income, so a conversion that’s good for your long-term taxes can be bad for your premiums two years out. The fix is precision, and IRMAA cooperates, because the brackets are known in advance and the surcharge is a cliff, not a slope.

The cliff that makes this manageable

Here’s the quirk that turns IRMAA into a planning tool instead of a trap: it’s a step function. Go one dollar over a threshold and you jump to the next surcharge tier for the entire year. There’s no gradual phase-in. That sounds brutal, and it is if you cross by accident. But it also means the target is crystal clear. You convert right up to the threshold and stop, and you owe zero surcharge.

For 2026, the standard Part B premium is $202.90 a month with no surcharge. A married couple filing jointly stays surcharge-free while their income is at or below $218,000. The first tier kicks in above that, adding $81.20 a month per person to Part B plus $14.50 for Part D. The next tier starts above $274,000 and adds $202.90 to Part B. Single filers hit the first tier above $109,000 and the second above $137,000.

So for a couple, the line to respect is $218,000 of income. Convert up to it, and your premium is the standard $202.90. Convert one dollar over, and you’ve signed up both spouses for an extra $81.20 a month on Part B and $14.50 on Part D, roughly $2,300 across the year for the couple.

The two-year lookback nobody remembers

The detail that catches people: IRMAA runs on a two-year delay. Your 2026 premiums are based on the income you reported for 2024. So a conversion you do this year doesn’t hit your Medicare bill now. It hits it two years from now.

That lag cuts both ways. It means you have to plan your conversions against the IRMAA brackets two years ahead, before you’re even on Medicare in some cases. It also means the years before you turn 63 are golden: convert aggressively at 60, 61, 62, and it never touches your Medicare premiums, because the lookback hasn’t reached those years yet. The moment your conversions start landing in the lookback window, the brackets become a hard ceiling.

A worked example

A 64-year-old couple, both on Medicare, has $150,000 of income before converting. They want to fill the 22% tax bracket, but they also want to dodge the IRMAA surcharge. The first IRMAA threshold for a couple is $218,000. That leaves $68,000 of room to convert before they trip the surcharge.

So they convert $68,000, landing right at $218,000. They pay tax at 22%, move a solid chunk into the Roth, and their Medicare premiums two years out stay at the standard rate. Convert $80,000 instead, and the extra $12,000 doesn’t just cost income tax. It costs the couple roughly $2,300 in surcharges on top, which works out to an ugly effective rate on that last slice of conversion.

If your accounts are large

When your tax-deferred balances are big, one year of bracket-respecting conversions won’t empty them, and that’s fine. The move is a multi-year ladder: convert up to a chosen IRMAA tier every year for a decade, accepting a tier you’ve deliberately chosen if the long-term RMD savings justify it. Sometimes paying into the first surcharge tier on purpose is the right call, because the future required minimum distributions you’re defusing would land in a far worse spot. The point isn’t to fear IRMAA. It’s to choose your tier with eyes open and never cross one by accident.

Watch the threshold, mind the two-year lag, and treat the bracket as a line you walk right up to. IRMAA punishes the dollar that crosses by surprise and rewards the conversion that stops on purpose. Knowing exactly where the line sits is the whole advantage.