These Were the 5 Worst-Performing Stocks in the S&P 500 in September 2025 — and One's Decline Can Be Tied to President Trump

It’s fun to follow stocks that soared recently, and it can be sobering to see which ones have plunged — especially if you’re a shareholder. So here’s a look at the worst-performing stocks in the S&P 500 index of 500 of America’s biggest companies — in September.

CarMax: Down 24.8%

CarMax (KMX -1.05%) sells, finances, and services new and used cars at more than 250 locations. Much of its loss happened after it posted a very disappointing second-quarter report, featuring revenue down year over year and profits really down — by 25%. This reflects lower car-buying enthusiasm from consumers.

FactSet Research Systems: Down 22.3%

FactSet Research Systems (FDS 1.57%) offers financial data and analytics for professional investors. It also posted results below analyst expectations.

Kenvue: Down 21.9%

Kenvue (KVUE -0.83%) was spun off from Johnson & Johnson in 2023 to focus on consumer products. Its brands include Listerine, Zyrtec, Motrin, Band-Aid, and… Tylenol. As you might have guessed, much of its recent downfall is tied to President Trump and others asserting that Tylenol is linked to autism.

Deckers Outdoor: Down 17.5%

Deckers Outdoor (DECK 3.56%) is an outdoor apparel company with brands such as Uggs, Teva, and Hoka. It has fallen in value in part due to concerns about tariff effects — as well as general worries about economic uncertainty reining in consumers’ eagerness to buy. It also disappointed investors with its last earnings report.

Synopsys: Down 16.7%

Synopsys (SNPS 2.46%) specializes in software used for designing and testing semiconductor chips. Its shares have fallen in part due to weakened demand from a major customer and export restrictions from the Trump administration (now removed).

While these stocks retreated, the S&P 500 index gained 3.5% in September. Remember, too, that when stocks plunge, you should steer clear if the company is facing lasting, intractable problems. But if the market seems to have overreacted and the company’s future is promising, a much lower stock price can be a great buying opportunity.