Merger Arbitrage

When Company A announces it will acquire Company B at $50 per share, Company B's stock might trade at $48. The $2 difference is the deal spread, representing the market's assessment of deal completion risk and the time value of money until closing. Merger arb funds analyze the probability of deal closure, expected timeline, and downside if the deal breaks to determine whether the spread offers an attractive risk-adjusted return. Spreads widen when deal risk increases (regulatory concerns, financing uncertainty) and narrow as closing approaches.

In a cash deal, the arbitrageur simply buys the target's shares and waits for closing. In a stock-for-stock deal, the strategy is more complex: the arbitrageur buys the target and simultaneously shorts the acquirer in the exchange ratio offered. This hedge locks in the spread regardless of market movement. For example, if Company A offers 0.5 shares for each Company B share, the arb buys B and shorts 0.5 shares of A for every share of B purchased. Mixed cash-and-stock deals require a blended approach.

The primary risk is that the deal fails to close, causing the target's stock to drop sharply — often back to pre-announcement levels. Common deal-breakers include antitrust regulatory blocks, failed shareholder votes, financing conditions not being met, or a Material Adverse Change (MAC) clause being triggered. A single deal break can wipe out months of gains from successful closes, which is why portfolio diversification across 20-40 concurrent deals is standard practice. Merger arb funds also assess break-up fee provisions, which provide a floor on the downside.

Merger arb returns are often modest in absolute terms (2-5% per deal) but attractive when annualized. A 3% return earned in 60 days annualizes to approximately 18%. Funds lever their portfolios (typically 2-4x) to amplify these returns. The key formula converts the deal spread into an annualized return: divide the spread percentage by the expected number of days to close, then multiply by 365. This allows comparison across deals with different spreads and timelines, enabling optimal capital allocation.