Background Note | HBS Case Collection | December 2007 (Revised January 2008)

Evaluating M&A Deals-Announcement Effects, Risk Arbitrage and Event Risk

by Carliss Y. Baldwin


The announcement of merger or acquisition conveys new information to the capital markets. This note describes how the stock prices of a Buyer and Target behave after the announcement of a deal. First, for an all-stock deal that is certain to go through, the note defines accouchement effects and describes the fundamental arbitrage relationship between Target and Buyer stock prices. It shows how post-announcement prices may be used to infer the market's estimate of synergies. It then explains how the betas of the two companies change post-announcement and the arbitrage relationship between prices in a cash-and-stock deal. Finally, it defines event risk and explains how it affects the prices of the Buyer and the Target.

Keywords: Mergers and Acquisitions; Announcements; Capital Markets; Stocks; Price; Risk and Uncertainty;


Baldwin, Carliss Y. "Evaluating M&A Deals-Announcement Effects, Risk Arbitrage and Event Risk." Harvard Business School Background Note 208-103, December 2007. (Revised January 2008.)