Are Merger Synergy Disclosures Credible?

We examine the credibility of synergy guidance in 12,176 U.S. mergers and acquisitions (M&A) announced between 2004 and 2021. Using press releases and conference call transcripts, we identify qualitative and quantitative synergy guidance and analyze its determinants, market reactions, and post-acquisition realizations. Synergy guidance is more common in larger, stock-financed deals, public-target acquisitions, related-industry transactions, and among acquirers with greater analyst coverage and prior guidance experience. Litigation risk deters disclosure, especially numeric guidance. Investors respond favorably to both textual and numeric guidance at announcement, with stronger reactions to more intensive discussion and higher numeric estimates. However, post-acquisition outcomes suggest that disclosed expectations are often not realized. Synergy disclosers experience more frequent and larger goodwill impairments and worse post-merger operating performance, and larger numeric estimates additionally predict downward revisions to synergy expectations and lower long-run stock returns. The impairment-disclosure association is attenuated when acquirers have greater forecasting experience and targets operate in richer information environments, consistent with learning and information quality constraining strategic bias and forecasting noise. Exploiting the 2013 U.K. Takeover Panel Rule 28 reform, we find that numeric guidance in U.K.-target deals predicts fewer subsequent goodwill impairments than comparable U.S.-target deals, consistent with mandated external verification improving disclosure credibility. Our findings inform ongoing policy debates by highlighting a disconnect between investors' favorable announcement reaction to synergy guidance and its limited long-run realization.