The Roth Conversion That Added $999.60 to a Retiree’s Medicare Bill…Two Years Later

Mary did everything the retirement books told her to do. At 68, already on Medicare and watching her traditional IRA balloon toward future required minimum distributions (RMDs), she pulled the trigger in 2024 on a large Roth conversion. The logic was sound: pay tax now at known rates, shrink the future RMD, leave heirs a tax-free account. What she did not price in was a bill that would not show up for almost two years, stealthily delivered by Medicare rather than the IRS.

This is a common story in retirement forums. Someone runs the conversion math, lands in a manageable tax bracket, then receives a notice in late 2025 explaining that their 2026 Medicare premiums are going up by thousands of dollars. The conversion was sound in principle. The problem was its size in a single tax year.

Why a 2024 Decision Shows Up on a 2026 Premium

The Social Security Administration (SSA) prices Medicare premiums using Modified Adjusted Gross Income (MAGI) from two tax years earlier, as explained in coverage of the hidden retirement tax. Mary’s 2024 conversion counts as ordinary income in 2024, so it lands on her 2026 premium. Her income returned to normal in 2025, meaning the surcharge is a one-year event. A Roth conversion does not qualify as a life-changing event on Form SSA-44, which is reserved for retirement, death of a spouse, or loss of pension.

The conversion pushed Mary’s 2024 MAGI into the single-filer tier greater than $205,000 and less than $500,000. That tier is where the Income-Related Monthly Adjustment Amount (IRMAA) gets expensive.

The Full Annual Hit

The $999.60 in the title is only the Part D piece. Here is what Mary actually pays in 2026:

1. Part B standard premium: $202.90 per month, what every Medicare beneficiary pays before any surcharge. The 2026 standard Part B premium is $202.90.
2. Part B IRMAA surcharge: $446.30 per month on top, bringing her total Part B to $649.20 per month. Over 12 months, that surcharge alone totals $5,355.60.
3. Part D IRMAA surcharge: $83.30 per month, or $999.60 for the year, added to whatever her drug plan already charges. The monthly Part D surcharge for her tier is $83.30.

Stack the Part B and Part D surcharges and the conversion cost Mary approximately $6,355 in extra Medicare premiums for this year, based on the 2026 Medicare Parts A & B Premiums and Deductibles released by CMS. That is on top of the federal income tax she already paid on the conversion the prior spring. It does not repeat in 2027 if her income normalizes, but there is no refund and no appeal.

How IRMAA Cliffs Work

IRMAA tiers behave like cliffs, not ramps, as Kiplinger has detailed in its IRMAA guidance. One extra dollar of MAGI can push a household into the next bracket, and the surcharge applies for the full year. Tax-exempt interest from municipal bonds gets added back into MAGI, so a portfolio built around munis for tax efficiency does not shield Medicare premiums. Capital gains, dividends, and year-end mutual fund distributions all count.

The fix in Mary’s case was timing rather than avoidance. Splitting the same conversion across three or four years, sized to stop just under the next IRMAA threshold each year, would have kept her in a lower tier and likely avoided the Part B surcharge entirely. Conversions completed before age 63 fall outside the two-year lookback window once Medicare begins at 65, which is why advisors encourage clients to begin conversions early.

Before You Convert

A Roth conversion can still be the right long-term move. The lesson is that a Medicare bill arrives alongside the tax bill. Before executing the conversion, run the projected MAGI against the current IRMAA tiers for the conversion year, then check where that income lands two years out. If a smaller conversion keeps a retiree a tier lower, the math almost always favors spreading it out.

The mistake hardest to undo is failing to treat the conversion as a two-year Medicare decision, not just a single-year tax one. A quick look at where MAGI sits relative to the next threshold is usually the most valuable hour spent before year-end.