Selling a losing stock before Dec. 31, 2026, is a familiar year-end strategy. Many retirees use realized losses to offset capital gains.

But for Social Security recipients, the same sale can potentially deliver a second tax benefit by reducing the portion of their benefits subject to federal income tax.

A single capital loss in a taxable brokerage account can trigger two tax breaks under the Internal Revenue Service (IRS) tax code: capital-loss deduction and reduction in the taxable portion of Social Security benefits.

The combined effect can strip several thousand dollars from taxable income by applying thresholds that Congress froze decades ago and has never adjusted.

Each cost-of-living adjustment (COLA) has pushed more retirees past those fixed lines, turning even a modest year-end deduction into larger savings, 24/7 Wall St reported.

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How one stock sale can trim two tax bills

The IRS allows capital losses to offset capital gains dollar for dollar. If losses exceed gains, taxpayers generally can use up to $3,000 of the remaining loss against ordinary income each year, with additional losses carried forward.

The second benefit applies to the combined income formula the IRS uses to determine how much of a benefit check is taxable, according to IRS Publication 915. When that $3,000 deduction lowers adjusted gross income, it reduces combined income and can shift benefits into a lower tier.

Christopher Stroup, president and financial advisor at Silicon Beach Financial, told GoBankingRates that retirees frequently underestimate how required withdrawals, dividends, and pension income add up to inflate their combined income calculation.

<strong>Many retirees don’t realize how these seemingly minor income sources interact with thresholds to increase their tax burden</strong>.

A filer with combined income above $34,000 owes federal tax on up to 85% of Social Security benefits under current rules. A retiree positioned near that threshold could use the full deduction to cross below it with a single year-end sale.

That shift could shrink taxable benefits by roughly $2,200, for a total income reduction near $5,200, 24/7 Wall St reported. At a 12% federal rate, combined savings reach about $624, though each filer’s deductions and bracket shape the final figure.

Why Social Security’s frozen thresholds matter

Congress first made Social Security benefits partially taxable under legislation enacted in 1983, the SSA reported, with the $25,000 threshold for single filers taking effect in 1984. 

The $34,000 upper threshold was added a decade later under the Omnibus Budget Reconciliation Act of 1993, which raised the taxable portion of benefits to up to 85% for higher-income retirees.

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Those dollar amounts were never indexed to inflation, so thresholds that once shielded most retirees now catch more households each year as wages, benefits, and investment returns climb past the 1984 lines, the SSA reported.

Each COLA raises benefits, which feed into the combined income formula through the half-of-benefits component, pulling recipients toward or past one of those lines. 

On a $30,000 annual benefit, a 3.5% adjustment adds about $525 to the combined income before any other source contributes, 24/7 Wall St showed.

Selling assets at a loss in a taxable account avoids the additional combined income that an individual retirement account (IRA) withdrawal would create, Schwab explained.

The double deduction amplifies the payoff for recipients near a bracket line, where one sale can shift which tier of benefit taxation applies.

Social Security’s outdated income thresholds expose more retirees to benefit taxes as COLAs rise, making tax planning and strategic asset sales increasingly important.

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The rules and account restrictions that can wipe out the deduction

The strategy comes with important limitations. The first is the IRS wash-sale rule. A taxpayer generally cannot claim a loss if they buy the same or a substantially identical security within 30 days before or after the sale.

If a wash sale applies, the loss is generally added to the basis of the replacement shares rather than immediately deducted.

Buying back inside an IRA within the 30-day window erases the tax benefit permanently, and no future sale restores the lost deduction. Losses in an IRA or 401(k) do not generate a deductible capital loss, so the strategy only works for positions held in taxable accounts.

Retirees in the 0% capital gains bracket can still raise their benefit taxes with a profitable sale, Ryan McKeown, financial advisor at Wealth Enhancement, told Kiplinger. Every sale still has to have its own investment logic, because “all the decisions need to be put in context of an overall plan,” McKeown said.

Automatic dividend reinvestment programs can also trigger a wash sale if they buy back shares of the same fund during the restricted window.

What retirees near a threshold should calculate before Dec. 31

The potential value of tax-loss harvesting depends heavily on how close a retiree is to a Social Security taxation threshold.

Matt Nadeau, wealth advisor, told Kiplinger that retirees should evaluate whether targeted loss harvesting can hold combined income below the 85% inclusion line.

Dividends, required minimum distributions, pension payments, and part-time wages all feed into the combined income, and running a year-end estimate is the first step, Nadeau said. 

Pre-retirement Roth conversions can also serve as a lever to lower adjusted gross income before benefits are included in the calculation, Nadeau noted.

Retirees below $25,000 or firmly above the 85% zone collect the standard capital loss deduction without triggering the second benefit from a bracket shift. 

Those in the middle should consult a tax professional before executing the sale to confirm the move aligns with an overall income strategy, McKeown recommended.

The payoff depends on proximity to a cutoff, and retirees within striking distance see the largest reduction from a single, well-timed December sale.

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