Amentum Stock Reverses Its Gains After Joining S&P 500

The newest stock to join the S&P 500 has had a volatile introduction to the stock market. After skyrocketing more than 22% to lead the benchmark index in their first day of trading on Monday, shares of Amentum Holdings (AMTM) gave up most of those gains Tuesday.

Amentum began trading this week as an independent public company following a spinoff from the engineering and construction firm Jacobs Solutions (J). Jacobs announced last year that it would separate its Critical Mission Solutions as well as its Cyber and Intelligence businesses to combine them with Virginia-based technology services provider Amentum to form the new entity. The merger between Amentum and the former Jacobs divisions was finalized last Friday.

Turbulent S&P 500 Debut

Coinciding with the Amentum stock’s first day of trading on Monday, the government services firm also became the newest addition to the S&P 500, replacing fragrance and personal care products retailer Bath & Body Works (BBWI) on the benchmark index.

With more than 20% upward and downward swings, the rise and fall of Amentum shares in their first two days of trading proved a dramatic welcome to the stock market. However, it is common for stocks joining the S&P 500 to experience a temporary rise as funds that track the widely followed index purchase the new constituent.

Amentum finished Tuesday at $25.75, off 20%. Jacobs shares, meanwhile, avoided any major price swings, ticking about 1.6% higher over the two sessions since the completion of the spinoff, ending Tuesday at $132.04. The company said the transformation will allow it to streamline operations and focus on higher-margin opportunities related to critical infrastructure and sustainability.