The acquisition of My Plan Manager by Arthur J. Gallagher & Co. is likely to have a positive short-term impact on AJG's stock price. Acquisitions can lead to synergies, expanded market share, and revenue growth. Although the financial terms were not disclosed, the market typically reacts positively to expansion news, especially when it involves entering new markets or enhancing existing services. The lack of financial details might temper the impact slightly, but overall investor sentiment is expected to be positive.