The Nasdaq-100 market index holds a lot of volatile stocks. Some of its top performers seem overvalued today, while others seem to have room for further growth. The index as a whole rose 9.1% last month, outpacing the S&P 500 (^GSPC -1.13%) return of 6.3%.
But what about the other end of the spectrum? Let's take a quick look at the two worst performers on the Nasdaq-100 in May 2025.
Regeneron: Down 18% in May
Biotech giant Regeneron (REGN 1.42%) was on track for a quiet May, holding almost exactly steady with just a couple of days left in the month. A disappointing earnings report changed that story in a hurry, driving Regeneron's stock 18% lower on the last trading day in May.
Regeneron's first-quarter sales fell 4% year over year, while adjusted earnings per share dropped 14% lower.
This is one of the most affordable large-cap biotech stocks today, but arguably for good reasons. The stock is down 48% over the last year, so I understand if you want to buy the dip. Just remember that the company is facing unprecedented challenges right now, and a strong development pipeline doesn't always result in blockbuster products.
Image source: Getty Images.
Copart: Down 15.6% in May
Online auto auction specialist Copart (CPRT -2.82%) also fell after reporting earnings in May. All the headline numbers were up year over year and roughly in line with analyst expectations, but market makers were looking for something more. Copart's stock trades at lofty valuation multiples such as 10.6 times sales and 33 times earnings. It doesn't take much of a miss to inspire a large price drop under these conditions.
Copart's stock is down 5% over the last year, but it remains a long-term winner with a market-beating three-year return and a stellar 1,030% gain over the last decade. Management argues that the company might benefit from tariff-based uncertainty, as expensive repair parts could result in more "total loss" insurance claims. If so, Copart's stock may be a great buy today -- but only time will tell how this theory works out.
