A 72-year-old retiree in Ohio posted a familiar story to a personal finance forum this spring: he had sold long-held stock in 2024 to write a $60,000 tuition check for his grandson’s freshman year. Two years later, his Medicare premium notice arrived with an unexpected surcharge, and he wanted to know if the Social Security Administration had made a mistake. It had not.
A realized capital gain counts as income on the tax return, that return feeds modified adjusted gross income (MAGI), and MAGI from two years back sets the current year’s Medicare Part B and Part D surcharges. The check went to the university. The IRS recorded the gain. Medicare read it as income.
Who This Actually Hits
The income-related monthly adjustment amount, or IRMAA, touches roughly 8% of people with Medicare Part B. A retiree whose combined income (Social Security, pensions, RMDs, interest, dividends, and realized gains) stays under the first threshold pays the standard premium. The trap opens once a one-time sale stacks on top of ordinary retirement income and pushes total MAGI past the first tier.
For 2026, that first tier begins at MAGI greater than $109,000 for individual filers and greater than $218,000 for joint filers. The standard Part B premium is $202.90 per month.
The Two-Year Lookback
The Social Security Administration uses the tax return from two years prior to set the current year’s IRMAA. Sell stock in 2024, and it shows up on 2026 premiums. Sell stock in 2026, and it lands on the 2028 notice. By the time the letter arrives, the money is long gone, spent on tuition, a roof, or a wedding.
Here is the 2026 grid for a joint-filing couple, straight from the CMS fact sheet:
| Joint MAGI | Part B surcharge (per person, monthly) | Total Part B premium (per person, monthly) | Part D surcharge (per person, monthly) |
|---|---|---|---|
| $218,000 or less | $0.00 | $202.90 | $0.00 |
| $218,001 to $274,000 | $81.20 | $284.10 | $14.50 |
| $274,001 to $342,000 | $202.90 | $405.80 | $37.50 |
| $342,001 to $410,000 | $324.60 | $527.50 | $60.40 |
| $410,001 to under $750,000 | $446.30 | $649.20 | $83.30 |
| $750,000 or more | $487.00 | $689.90 | $91.00 |
Each surcharge is per person, per month. A couple pushed into the first tier by a tuition-driven stock sale pays both Part B and Part D adjustments on both spouses, every month, for the full year.
Why the Sale Compounds Retirement Income
The capital gain only needs to be large enough, when added to Social Security, pensions, required minimum distributions, and investment income, to push MAGI over the next threshold. A couple already at $200,000 of ordinary retirement income needs only a modest realized gain to cross into IRMAA territory. Municipal bond interest, which many retirees treat as invisible, counts too. MAGI for IRMAA is adjusted gross income plus tax-exempt interest.
The 2026 Social Security COLA of 2.8% raises the ordinary-income baseline for every beneficiary, meaning the same tuition-sized gain crosses a threshold more easily this year than last. With the 10-year Treasury yield at 4.62%, retirees weighing whether to sell stock or lean on bond income are more likely to realize gains than in the low-rate era.
One consolation: IRMAA resets annually. A one-time gain in 2024 typically affects only the 2026 premium and drops off in 2027 if income normalizes. For readers who want to model how a lump-sum withdrawal or sale interacts with retirement premiums, the Medicare’s Hidden Bills report walks through the arithmetic in detail.
What to Do Before the Sale
- Estimate MAGI for the sale year before pulling the trigger. Add expected Social Security (the taxable portion), pensions, RMDs, interest (including municipal), dividends, and the projected gain. Compare the total to the joint $218,000 or individual $109,000 line.
- Split the sale across two tax years if the gain would cross a tier. Half in December, half in January can keep both years under the threshold and avoid the surcharge entirely.
- Consider gifting appreciated shares directly to a 529 or to the grandchild. The gain shifts to the recipient’s return, often at a 0% long-term capital gains rate for a student, and never touches the grandparent’s MAGI.
- Do not count on Form SSA-44 to rescue a voluntary sale. The life-changing event exception covers work stoppage, spousal death, divorce, and similar triggers. Selling stock to pay tuition is not on that list.
The generosity was real. The tax code reads it in dollars, and Medicare reads the tax code.
Contact [email protected] for any questions or corrections.
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