Case Study: Sequencing a Capital Gain Around the Senior Deduction and IRMAA
One retired couple, one decision: sell a large gain in one year or split it across two. The senior deduction, the capital gains brackets, and IRMAA all key off the same MAGI number, and this case study walks through what each option actually costs.
The couple
Both spouses are 66, retired, and on Medicare. Their baseline income is $100,000 a year. They are sitting on a $120,000 long-term capital gain from a taxable brokerage account and want to sell to fund a home purchase.
Option A: sell the full $120,000 gain in one year
MAGI for the year is $100,000 plus the $120,000 gain, or $220,000. That is $70,000 over the $150,000 MFJ senior deduction threshold, which cuts the new $12,000 senior deduction by 6% of $70,000, or $4,200, down to $7,800. Total deductions (standard deduction plus age add-on plus reduced senior deduction) come to $43,300, leaving $176,700 of taxable income.
| System | Effect |
|---|---|
| Senior deduction | Reduced from $12,000 to $7,800 by the phase-out. |
| Capital gains bracket | About $77,800 of the gain lands in the 15% bracket instead of 0%, costing roughly $11,670 in federal tax on the gain. |
| IRMAA (2 years later) | $220,000 MAGI crosses the $218,000 joint threshold. The couple triggers the first IRMAA tier for the year their 2-year-old income is checked, adding roughly $2,296 a year in Medicare premiums for the two of them. |
Option B: split the sale into $60,000 per year over two years
Each year, MAGI is $100,000 plus $60,000, or $160,000, just $10,000 over the senior deduction threshold. That trims the senior deduction only slightly, from $12,000 to $11,400. Taxable income each year comes to about $113,100, and the gain stacks mostly inside the 0% capital gains bracket, with only about $14,200 spilling into the 15% bracket, roughly $2,130 in tax on the gain each year, or $4,260 total across both years.
| System | Effect |
|---|---|
| Senior deduction | Preserved at $11,400 of $12,000 in both years, nearly the full amount. |
| Capital gains bracket | Most of the gain stays in the 0% bracket. Total tax on the gain across both years: about $4,260, versus $11,670 for the single-year sale. |
| IRMAA (2 years later) | $160,000 MAGI stays comfortably under the $218,000 threshold in both years. No surcharge triggers at all. |
The bottom line
Splitting the sale saves roughly $7,400 in capital gains tax, avoids an IRMAA surcharge worth over $2,000 a year, and preserves an extra $3,600 combined of senior deduction across the two years, all from the same total $120,000 gain, just sequenced differently. None of these three effects would show up if this couple only checked one system before selling.
The general lesson
MAGI is the single number that the senior deduction, capital gains brackets, and IRMAA all key off. A move that looks fine when checked against one system can be expensive against another, and the only way to know is to check all three before selling, converting, or withdrawing, not just the one you happen to be thinking about. Use the senior deduction calculator, the capital gains brackets page, and the IRMAA brackets page together, or read the MAGI laddering guide for a systematic approach across multiple years.
Frequently asked questions
How does a capital gain affect the senior deduction?
A capital gain adds to your MAGI. If that pushes you over the $75,000 single or $150,000 married threshold, your senior deduction shrinks by 6 cents for every dollar over the line.
Does selling investments affect my Medicare premium?
Yes, with a two-year delay. IRMAA uses your MAGI from two years earlier, so a large gain this year can raise your Medicare Part B and D premiums two years from now if it pushes you over the IRMAA threshold.
Is it better to sell all at once or split a capital gain across years?
It depends on your baseline income relative to the capital gains 0% bracket, the senior deduction phase-out, and the IRMAA threshold. Splitting the sale often keeps more of the gain in the 0% bracket and protects the senior deduction and IRMAA in cases where a single large sale would cross a threshold.
What MAGI thresholds should retirees watch when selling investments?
The senior deduction phase-out ($75,000 single / $150,000 married), the capital gains 0% bracket ceiling ($49,450 single / $98,900 married taxable income), and the IRMAA threshold ($109,000 single / $218,000 married, based on income from two years earlier).