At 68, He Will Sell the S&P 500 Fund He Bought in 1996 to Move Into Bonds. The $310,000 Gain Will Push Him Into a Higher Medicare Premium Bracket in 2028
Selling a decades-old index fund to shift into bonds sounds like a straightforward retirement move, but a capital gains windfall can quietly trigger a Medicare surcharge that arrives two years later and costs far more than most retirees ever anticipate.
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Consider a hypothetical 68-year-old who bought an S&P 500 index fund in a taxable brokerage account in 1996. He now wants less stock risk and plans to sell and move into bonds. The 10-year Treasury yielded 4.91% on November 2, so the switch looks reasonable. For a sense of scale, the SPDR S&P 500 ETF Trust (NYSEARCA:SPY) has risen 466.8% in price since November 1999 alone.
His sale locks in a $310,000 gain. He has budgeted for the capital gains tax. The Medicare bill that shows up two years later has not crossed his mind.
The Medicare income surcharge, IRMAA, reaches about 8% of Part B enrollees. A single filer with MAGI of $109,000 or less ($218,000 joint) pays the standard $202.90 a month. Most retirees sit comfortably below that line. One large sale can push a modest-income retiree over it for a year.
Why Selling a Fund Changes Medicare Income
Social Security sets IRMAA using the most recent federal tax return the IRS provides, which usually means the return from two years earlier. A sale in 2026 sets his 2028 premiums. SSA defines MAGI as total adjusted gross income and tax-exempt interest income.
Where the fund is held determines everything. Trades inside a traditional IRA or Roth IRA never reach Form 1040, so swapping stocks for bonds there adds nothing to MAGI. A sale in a taxable brokerage account sends the gain through Schedule D and straight into AGI.
Get the basis right before you sell. Every reinvested dividend was taxed in the year it was paid, and each one raised his cost basis. Thirty years of reinvestments can shrink the true gain a lot. The $310,000 figure here assumes those dividends are already included.
A $310,000 Gain on Top of $80,000 in Income
Assume he files single and has $80,000 in other MAGI. Without the sale, he pays the standard premium. The gain raises his MAGI to $390,000, which lands in the single bracket of over $205,000 up to $500,000. Using 2026 rates, Part B rises to $649.20 a month, including a $446.30 surcharge. If he has Part D coverage, an $83.30 monthly surcharge comes on top. Together, those surcharges total $6,355.20 annually. Actual 2028 premiums have yet to be announced.
A married couple filing jointly at the same income pays $527.50 each for Part B, and both spouses pay it. After a spouse dies, the survivor may eventually face the lower single-filer thresholds. That can increase Medicare premiums even if income changes little.
Selling in stages can backfire. Single filers with MAGI above $200,000 may also owe a 3.8% net investment income tax on some or all of their investment gains. The table applies the 2026 brackets to every year.
| Plan | MAGI per year | Total IRMAA surcharge, all years (Part B + D, single) | Total 3.8% NIIT, all years |
|---|---|---|---|
| Sell all in one year | $390,000 | $6,355.20 | $7,220 |
| Split over two years | $235,000 | $12,710.40 | $2,660 |
| Split over three years | $183,333 | $13,860 | $0 |
Using fixed 2026 Medicare brackets, the two-year split costs the most at $15,370.40 in combined surcharges and investment taxes. One sale totals $13,575.20, while a three-year split comes to $13,860. Those figures exclude regular capital gains taxes and assume his other income stays unchanged.
Bonds Don’t Undo the Sale
Buying bonds with the proceeds leaves the gain on his tax return. The bonds also raise his MAGI every year after that. While it may feel tax-free, SSA adds tax-exempt interest from municipal bonds back into MAGI. Treasury interest counts as taxable income too. A bond portfolio built to lower risk can raise his ongoing income enough to put him near the first bracket (we explained IRMAA and the other premium traps retirees walk into, and you can read our free Medicare guide here: Medicare’s Hidden Bills).
There is no escape through Form SSA-44. Social Security allows relief after qualifying life changes, including retirement, reduced working hours or the death of a spouse. Selling a fund by choice doesn’t qualify on its own.
Three Checks Before Placing the Order
- Rebalance inside retirement accounts first. If he holds stocks in an IRA, he can sell them there and buy bonds there, then keep the taxable fund. Heirs generally receive a new cost basis based on the investment’s value at death, potentially eliminating decades of unrealized gains.
- Pull every tax lot. Choose specific-lot identification and sell the highest-basis shares first, starting with recent reinvestments. Then rerun the estimated gain against the bracket edges at $137,000, $171,000 and $205,000.
- Pick the tax year on purpose. A December 2026 sale sets his 2028 premiums. A January 2027 sale moves the hit to 2029 and gives him another year to collect basis records. If he chooses a staged plan, he should commit to the full split before the first trade.
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Gerelyn Terzo is the author of dividend investing handbook "Dividend Investing Strategies: How to Have Your Cake & Eat It Too." A veteran financial journalist, she covers agri-finance for outlets like Global AgInvesting and the broader stock market and personal finance for 24/7 Wall Street. She began at CNBC and later helped launch Fox Business in New York. Gerelyn currently resides in Woodland Park, Colorado and dabbles in nature photography as a hobby.
