The Roth Conversion That Accidentally Triggered $4,000 in Medicare Surcharges

A 64-year-old retiree converts $150,000 to a Roth in 2024, feeling smart about reducing future required minimum distributions. Two years later, his Medicare bill arrives nearly $400 higher per month than expected. The culprit is a rule most retirees have never even heard of, and it changed the course of history for this retiree.

The Two-Year Lookback Rule

Medicare uses your tax return from two years ago to set premiums, not your current income. When this retiree enrolled in Medicare in 2026, the Social Security Administration examined his 2024 tax return, the same year he did the conversion. His modified adjusted gross income (MAGI) without the conversion was $35,000, a combination of Social Security and a small pension, would have qualified him for the standard Medicare Part B premium of $203 per month.

What happened? The $150,000 conversion pushed his 2024 MAGI to $185,000. That landed him in an IRMAA tier (Income-Related Monthly Adjustment Amount) where Part B costs $527.50 per month. The result: $3,895 in extra Part B premiums for the year, plus roughly $840 in Part D surcharges, totaling total IRMAA bill of approximately $4,735. One tax move, one $4,735 surprise.

A Reddit user described an identical situation: “In 2024 I converted IRA to Roth, which raised my income substantially, and triggered an IRMAA fee for 2026.” It is a predictable consequence of a rule most financial planning conversations skip.

According to Kiplinger’s Medicare planning guide, converting to a Roth before age 63 is especially advantageous because most individuals enroll in Medicare at age 65, meaning income before 63 will not impact Medicare premiums. This retiree converted at 64, placing the conversion squarely in the two-year lookback window.

Was the $4,735 Hit Worth It?

Probably yes. The $150,000 conversion removes $150,000 from a traditional IRA. Left to grow for roughly 11 years before required minimum distributions begin at age 73, that money would reach approximately $256,000. The annual RMD on that amount would be roughly $9,660, generating 24% tax bracket, that is about $2,318 saved every year in ongoing taxes. Over 15 years of RMDs, total tax savings approach $34,770, far outpacing the IRMAA cost.

Financial planner Nancy Gates cited by Kiplinger explained, “Typically, the tax hit is worth it” when weighing one year of higher Medicare premiums against years of lower RMD taxes. The real problem was the surprise, not any flaw in the conversion strategy itself.

What to Do Before Converting

Before converting, map out what your MAGI will look like two years later when Medicare reads that return. The IRMAA threshold for a single filer begins at $109,000. Each bracket jump adds hundreds of dollars per month. Converting just below a cliff costs far less than crossing it by accident.

If a large conversion is unavoidable, Roth conversions must be completed three years before applying for Medicare to clear the two-year lookback window entirely. For most Americans, that means finishing conversions by age 62 or 63. Income from pensions, dividends, or part-time work shifts the calculus considerably, so running the numbers with a tax professional before converting is worth the time in spades.