The IRMAA Cliff: How One Dollar of Income Can Cost a Couple $2,300 in Medicare Premiums

Hal and Carol did a tidy little Roth conversion in 2024, squeezing in some extra income while the market was down, exactly the kind of move the planning blogs applaud. What nobody flagged was the dollar amount. Their conversion pushed their joint income to $218,400, $400 over a Medicare line they had never heard of. They felt nothing in 2024. Then in 2026 the bill arrived: about $2,300 in extra Medicare premiums for the year, the two of them combined, triggered by being a few hundred dollars over a threshold two years earlier. (Hal and Carol are a composite; the brackets and dollar figures are the real 2026 CMS numbers.)

Here is the detonating fact. IRMAA, the income-related surcharge on Medicare Parts B and D, is a cliff, not a ramp. Go $1 over the first joint threshold of $218,000 ($109,000 single) and you do not pay a surcharge on the dollar over. You pay the full tier surcharge, on premiums, for the entire year. One dollar of income, roughly $2,300 of cost for a couple.

How a ramp pretends to be a cliff

Income tax phases in. Earn one more dollar in a higher bracket and only that dollar is taxed more. IRMAA does the opposite. The moment your modified adjusted gross income crosses a line, the surcharge for that whole tier attaches to every month's premium.

For 2026, the standard Part B premium is $202.90 a month. Cross the first threshold and it jumps to $284.10, a surcharge of $81.20 a month, or about $974 a year per person, plus a Part D surcharge of $14.50 a month (about $174 a year). For a married couple both on Medicare, that first step costs roughly $2,297 for the year. At the top tier ($500,000 single / $750,000 joint), the total Part B premium reaches $689.90 a month, a surcharge approaching $487 a month per person.

And here is the part that ambushes people: it is keyed to your income from two years ago. Your 2026 surcharge is set by your 2024 tax return. A one-time event in 2024, a Roth conversion, a capital gain, a property sale, a large required distribution, reaches forward two years and lands when you have long since forgotten it.

What it costs to clip the line

Hal and Carol's $400 overage tells the story in one number. A few hundred dollars of conversion income over the line triggered roughly $2,300 in combined surcharges for 2026, an effective tax on that overage of several hundred percent.

A single retiree who sells a vacation property and lands $1 into the second tier pays an extra $81.20-plus a month all year, well over $1,000, for a gain that had nothing to do with Medicare.

Same incomes, wildly different outcomes, decided entirely by which side of a line they landed on, and whether anyone was watching the dollar amount when it happened.

Why careful planners walk into it

The cruel irony is that IRMAA most often snags the organized retiree, the one doing Roth conversions, harvesting gains in a low year, managing withdrawals deliberately. Every one of those smart moves raises income. The two-year lookback hides the consequence so far downstream that the cause and the cost never sit on the same page. You optimize your 2024 taxes, feel good, and get the invoice in 2026 from a different agency entirely. If this sounds familiar, the companion piece on the most expensive dollar follows one retiree through it.

What to actually do

• Know your two lines. For 2026 premiums, based on 2024 income, the first thresholds are $109,000 single and $218,000 joint. When you do anything that adds income, check the running total against the line before December 31 of that year.
• Convert and harvest up to the line, not over it. Bracket-filling and Roth conversions are still smart. Just size them to stop short of the next IRMAA threshold. The last few thousand dollars can cost more than they are worth.
• Mind the two-year clock. The income that matters for your first Medicare year was earned before you enrolled. Plan the runway in your early 60s, not at 65. Keeping more income in tax-free accounts like an HSA is one way to hold the line.
• Appeal a one-time spike. If your income dropped because of a qualifying life-changing event, retirement, loss of a pension, divorce, or the death of a spouse, file Form SSA-44 to have IRMAA recalculated on your current income instead of the two-year-old figure.

Only about 8% of Medicare beneficiaries pay IRMAA, but the ones who do are disproportionately the savers with deferred balances and deliberate income plans. If that is you, the line is worth memorizing.

The rules, stacked

• IRMAA is a cliff. One dollar over costs the whole tier, all year.
• The income that sets your premium is two years old. Plan backward from the bill.
• Convert up to the line. The dollar past it is the most expensive one you will earn.
• A one-time spike is appealable. Know the form before you need it.

Hal and Carol are a composite; figures are the official 2026 CMS amounts. Educational only, not individualized tax or financial advice; consult a qualified advisor before timing conversions or sales. Sources: CMS 2026 Medicare Parts A and B premiums; 2026 IRMAA brackets ($109,000 single / $218,000 joint first tier; Part B $202.90 base, $284.10 to $689.90 with surcharge; Part D $14.50 to about $91; top tier $500,000 / $750,000; two-year lookback to 2024); SSA Form SSA-44 (life-changing-event appeal); Kiplinger, June 2026.