Hedging a Stock-for-Stock Deal

Some acquisitions are paid for in cash — the target's shareholders simply receive a fixed dollar amount per share. Others are paid for in stock: for every share of the target a shareholder owns, they receive a fixed number of shares in the acquirer. A merger-arb trader who wants to bet on the deal actually closing, without also betting on where the acquirer's stock goes in the meantime, needs to hedge that second risk out — and the size of that hedge is the exchange ratio, the number written directly into the deal terms.

Why the exchange ratio is the hedge ratio

If a deal specifies that each target share converts into 0.5 shares of the acquirer, then a trader who buys one share of the target and wants to be flat to the acquirer's stock price simply shorts 0.5 shares of the acquirer. Once the deal closes, the long target share turns into 0.5 acquirer shares, which exactly offsets (closes out) the 0.5-share short position. Whatever happens to the deal spread between now and closing — it narrowing as the deal looks more certain, or blowing out if there's regulatory trouble — is isolated from whatever the acquirer's stock does day to day, because the hedge tracks it share-for-share.

A worked example: a target trades at $38 and the acquirer at $80, with a deal offering 0.5 acquirer shares per target share (worth $40 at the acquirer's current price). The trader buys the target at $38 and shorts 0.5 shares of the acquirer at $80, i.e. $40 of exposure. The $2 gap between $38 and $40 is the arbitrage spread being captured — compensation for the risk the deal doesn't close, the time value of money until it does, and the acquirer's own stock risk in the meantime, which the short position is there to remove. If the acquirer's stock rallies to $90 before closing, the short leg loses money, but the long target position (now worth 0.5 × $90 = $45 once converted) gains by an offsetting amount — the trader's profit or loss depends on the spread, not the acquirer's stock level.

What this means in practice

Real deals complicate the ratio: some have collars that adjust the number of acquirer shares delivered if the acquirer's stock moves outside a range before closing, and some let target shareholders elect cash, stock, or a mix, which changes the effective ratio for the book as a whole. A trader has to track the deal's exact terms, not just its headline exchange ratio, and rebalance the hedge if the acquirer issues new shares, pays a special dividend, or the terms are amended mid-deal.