How a Roth Conversion at 64 Added $1,116 to a Retiree’s Medicare Premiums Two Years Later

A Smart Tax Move That Backfired

A 64-year-old single retiree pulls in about $60,000 a year from a pension and modest 401(k) withdrawals. Her advisor mentions the 22% federal bracket has room, and a Roth conversion looks smart before required minimum distributions (RMDs) arrive at age 73. She converts $60,000 from her traditional IRA. The federal tax bill stings but is manageable. Two years later, a letter from Social Security reveals that her Medicare premiums have jumped by roughly $93 a month for the entire year. That’s about $1,116 she never budgeted for, and it has almost nothing to do with her current income.

This scenario shows up routinely on retirement forums. Someone runs the conversion math, pays the income tax, feels confident about the long-term plan, and then gets blindsided by an Income-Related Monthly Adjustment Amount (IRMAA) surcharge two years later. The online calculator didn’t flag it, and now the bill has arrived with no way out.

The One Detail That Drives the Outcome

Medicare premiums are income-tested, but the clock runs on a two-year delay. Your modified adjusted gross income (MAGI) from 2026 determines what you pay for Part B and Part D in 2028. A 2026 conversion could affect your 2028 Medicare premiums because the entire conversion amount is added to MAGI in the year you do it.

For a single filer, the first IRMAA tier in 2026 kicks in at MAGI above $109,000. Without the conversion, this retiree’s MAGI sits at $60,000, well below the threshold, and she pays the standard Part B premium of about $203 a month with no Part D surcharge. With the $60,000 conversion stacked on top, MAGI jumps to $120,000. That thrusts her into the first tier for single filers, where the Part B adjustment runs about $81 a month and Part D adds roughly $14 more. Combined, that extra $93 a month adds up to about $1,116 across the year.

The IRMAA cliff works as a step function. Going one dollar over $109,000 triggers the entire tier-1 surcharge. The retiree pays the higher premium for a single year, tied to her age-64 income, and then it drops back to baseline once her MAGI normalizes. So the $60,000 conversion costs her income tax up front plus a one-year, $1,116 Medicare premium hike she will likely never see coming on a planning spreadsheet.

How It Connects to the Rest of the Picture

A large conversion can push more of her Social Security benefits into the taxable range, since provisional income climbs as conversion dollars flow into MAGI. If she had been planning to start Social Security at 65 or 66, the same conversion year could mean a meaningfully higher tax bill on those benefits.

The interaction with future RMDs is what made the conversion attractive in the first place. Shrinking the traditional IRA now means smaller forced withdrawals later, which can keep her under IRMAA thresholds in her 70s. The strategy is sound, but the execution is where most people slip. Here’s why: the conversion amount lands in MAGI all at once, and that spike triggers the surcharge.

What to Think Through Before You Convert

Two ideas tend to matter more than the rest:

1. Stage the conversion across multiple years. Splitting $60,000 into three $20,000 chunks keeps MAGI at roughly $80,000 each year, comfortably under the $109,000 single threshold. The total tax bill is similar, but no IRMAA surcharge is triggered. Converting just enough to hit the top of your current bracket without any money spilling over is the cleanest version of this rule.
2. Finish big conversions before age 63 if you can. Because of the two-year lookback, conversions done at 62 or earlier stay clear of Medicare’s lookback window before age 65. After that, every conversion year is a potential premium surprise two years later.

One last thing: the SSA-44 life event form lets you appeal an IRMAA surcharge after a qualifying life-changing event like retirement, marriage, or death of a spouse. A voluntary Roth conversion doesn’t qualify. Once the surcharge year hits, there is no graceful way out.

Conversions remain one of the most powerful tools in long-term tax planning. The math rewards patience over enthusiasm, and a single conversation with someone who understands how IRMAA, Social Security taxation, and bracket management interact can pay for itself many times over.