S&P Dow Jones Indices said The Trade Desk will be added to the S&P 500 prior to the start of trading on July 18, replacing engineering-software company Ansys. The reshuffle will alter the benchmark’s composition and could prompt index-tracking funds to adjust their holdings to reflect the new weighting. Ansys is being removed because it is set to be acquired by Synopsys, a transaction scheduled to close on July 17. Once the deal is completed, Ansys’s stock will cease to trade independently, freeing its slot in the large-cap gauge for The Trade Desk. The announcement sent The Trade Desk’s shares up as much as 15% in post-market trading, while Ansys shares were little changed. Inclusion in the S&P 500 often boosts demand for a company’s stock as passive funds linked to the index buy shares to mirror the benchmark.