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.