How $50,000 in Capital Gains Made 85 Percent of Social Security Taxable for Retirees

"The mechanism driving almost everything is the Social Security provisional income formula: adjusted gross income (AGI), plus any tax-exempt interest, plus half of Social Security. For this couple, that works out to $40,000 from the RMD, $50,000 in gains, and $24,000 representing half of their benefits, for a total of $114,000. For married filers, the threshold above which up to 85% of benefits become taxable is $44,000. They are nearly triple it. So $40,800, or 85% of their $48,000 in benefits, gets pulled into taxable income."

"Most retirees miss this detail: those thresholds, $32,000 and $44,000 for couples, were written into law in 1984 and have never been indexed to inflation. The Consumer Price Index has climbed from a base value of 100 in the early 1980s to roughly 332 today. What was once a high-income trigger now catches almost anyone with a pension or RMDs."

"Even without the gains, their provisional income would have been $64,000, still well over the threshold. The RMDs alone would have made most of their Social Security taxable. The capital gains landed on top of a structure already at its ceiling."

"They are both 67, file jointly, and collect $48,000 in combined Social Security. A traditional IRA required minimum distribution (RMD) of $40,000 lands every year. This year they realized $50,000 of long-term capital gains in their taxable account. Just a rebalance."

A retired couple sold mutual funds to rebalance a brokerage account and later found that 85% of their Social Security became taxable, increasing their federal tax bill. They are 67, file jointly, and receive $48,000 in combined Social Security. Their traditional IRA RMD is $40,000, and they realized $50,000 of long-term capital gains in the taxable account. Social Security provisional income equals AGI plus tax-exempt interest plus half of Social Security. In their case, $40,000 from the RMD plus $50,000 of gains plus $24,000 from half of benefits totals $114,000. For married filers, up to 85% of benefits become taxable above a $44,000 threshold, so $40,800 of benefits becomes taxable. The thresholds were set in 1984 and have not been indexed to inflation, so many retirees are now caught by the same limits.

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