How Your 401(k) Is Quietly Adding $3,500 a Year to Your Medicare Premium

A 65-year-old single retiree with $1.4 million in a traditional 401(k) sets up what looks like a comfortable income plan. She pulls $90,000 a year from the 401(k), adds a small pension and a brokerage dividend stream, and lands at a modified adjusted gross income near $175,000. Her tax bill is manageable. Her Medicare bill is the surprise.

That MAGI puts her squarely in the third IRMAA tier for 2026, the bracket covering single filers with income between $171,000 and $205,000, based on the 2024 return she filed last spring. The income test runs on a two-year lookback. That two-year lag is the detail most retirees miss entirely until the letter from Social Security arrives.

What the surcharge actually costs

The standard Part B premium in 2026 is $202.90 a month, a nearly 10% jump from the $185 charged in 2025. Her tier 3 IRMAA loading adds another $324.60 a month onto Part B and $60.40 a month onto Part D, bringing the total premium surcharge to about $385 a month, or roughly $4,600 a year. Had her MAGI landed in tier 2 (between $137,000 and $171,000), the combined add-on for Part B would have been $202.90 and the Part D surcharge $37.50 per month, or roughly $2,900 a year. The $3,500 figure in the headline reflects the midpoint of that range, where most retirees in this income profile actually land.

The numbers compound a pain retirees are already feeling. The 2026 Social Security cost-of-living adjustment came in at 2.8%, while the Part B premium climbed nearly 10%, almost four times as fast. For a beneficiary subject to tier 3 IRMAA, the base annual Part B cost alone clears $2,400 before a single doctor visit or prescription is paid. Add the surcharge and that figure climbs well past $6,000. Premium growth at this pace systematically outruns the purchasing power adjustment built into Social Security.

Why a single year of income two years ago controls today’s premium

The mechanic that quietly does the damage is the lookback. Social Security uses the most recent tax return information available from the IRS, which is almost always two years stale. A retiree who took a one-time income event at 63, whether a Roth conversion, the sale of a vacation property, an inherited IRA distribution, or a final-year bonus, will see the IRMAA bill arrive at 65 with no warning. The high-income year is gone. The surcharge is not.

The problem deepens where IRMAA interacts with other rules. Pulling an extra $5,000 from the 401(k) to cover the higher Medicare bill raises MAGI, which can push more Social Security benefits into the taxable column, which raises MAGI again. A retiree in the 22% federal bracket who triggers both the IRMAA cliff and Social Security taxation faces an effective marginal rate approaching 40 cents on the next dollar withdrawn. That compounding feedback loop is one of the most expensive planning blind spots in retirement income design.

Three moves that change the math

1. Run Roth conversions before the 63rd birthday, not after. The two-year lookback means a conversion done at 62 lands on the return that controls Medicare premiums at 64, before Part B even starts. A conversion at 63 or 64 controls premiums at 65 and 66, the most expensive years to get this wrong. Model the conversion against the next IRMAA threshold, not just the next federal tax bracket.
2. File Form SSA-44 if income legitimately drops. Retirement itself is a qualifying life-changing event under the rules. So is the death of a spouse, divorce, marriage, work reduction, loss of pension income, or loss of income-producing property due to circumstances outside the retiree’s control. The form takes one page and can erase the surcharge for the year. One important limitation: voluntary income events such as Roth conversions or investment sales do not qualify, because the form is designed for income reductions caused by external circumstances, not by the retiree’s own choices. Most people who qualify for SSA-44 relief never file it.
3. Use qualified charitable distributions starting at age 70½. In 2026, the maximum QCD is $111,000 per person, up from $108,000 in 2025. A QCD sends money directly from an IRA to a qualifying charity, satisfying the RMD requirement while keeping the dollars out of MAGI entirely, which means they never enter the IRMAA calculation. The One Big Beautiful Bill Act, signed in 2025, added a new 0.5% AGI floor on itemized charitable deductions and capped the tax benefit of those deductions at 35% for top-bracket filers. A QCD bypasses both restrictions completely, since the exclusion happens at the income level rather than the deduction level. For charitably inclined retirees, the QCD remains the cleanest single tool available for holding premiums at the lowest tier.

The IRMAA letter is a price tag attached to a return filed two years ago, paid in monthly installments out of a Social Security check. With the 2026 Part B premium consuming a growing share of those checks, fixed-income households cannot afford to hand back $3,500 to $4,600 a year for a tier they could have planned around. The planning window closes the day a high-income tax return is filed. After that, it is just arithmetic.

Editor’s note: This article was updated to include the confirmed 2026 Social Security COLA of 2.8%, which was used to illustrate the gap between benefit growth and the nearly 10% rise in the Part B premium. The description of Form SSA-44 was expanded to note that voluntary income events such as Roth conversions do not qualify as life-changing events for appeal purposes. The discussion of the One Big Beautiful Bill Act was also refined to specify the 0.5% AGI floor and 35% top-bracket cap on itemized charitable deductions that make QCDs more advantageous for high-income retirees.

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