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 in the fourth 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, which is the part most retirees miss until the letter from Social Security arrives.
What the surcharge actually costs
The standard Part B premium in 2026 is $203 a month. Her tier 4 IRMAA loads another $325 a month onto Part B and $60 a month onto Part D, for a total premium add-on of about $385 a month, or roughly $4,600 a year. If her MAGI had landed in tier 3 instead (between $137,000 and $171,000), the combined surcharge would have been about $240 a month, or $2,900 a year. The midpoint of that zone, where most readers in this profile actually live, is the $3,500 figure in the headline.
The numbers matter because they compound a problem retirees are already feeling. Healthcare services spending hit $3,741.3 billion in March 2026, almost matching housing as the largest category in personal consumption. CPI is sitting at 330.3, with March alone adding 1.1%, and Core PCE has climbed steadily to 129. Premiums are running ahead of inflation.
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 IRS return on file, which is almost always two years stale. A retiree who took a one-time event at 63, 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.
It gets worse where it interacts with other rules. Pulling another $5,000 from the 401(k) to cover the higher Medicare bill increases 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IRMAA cliff and Social Security taxation is looking at an effective marginal rate close to 40 cents on the next dollar withdrawn.
Three moves that change the math
- 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 in a tax planner against the next IRMAA threshold, not just the next federal bracket.
- 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, loss of pension income, or sale of an income-producing property. The form takes one page. It can erase the surcharge for the year. Most people who qualify never file it.
- Use qualified charitable distributions starting at 70.5. A QCD sends up to $108,000 per person in 2026 directly from an IRA to a charity. The dollars satisfy the RMD but never appear in MAGI, which keeps them out of the IRMAA calculation entirely. For charitably inclined retirees, the QCD is the cleanest tool in the box for keeping premiums in 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 that accounted for $1.6 trillion in transfer income last quarter. With consumer sentiment at 53.3, deep in pessimistic territory, 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 gets filed. After that, it is just arithmetic.
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