Deal Spreads and Break Risk

When Company A announces it will buy Company B for $50 a share in cash, B's stock doesn't jump straight to $50. It trades at, say, $48.50 — a discount that persists all the way to the deal's closing date. That $1.50 gap is the deal spread, and it exists for one reason: there's a real chance the deal never closes. Merger arbitrage is the business of buying that spread, share by share, deal by deal, and its entire economics come down to whether the spread you're paid is bigger than the loss you'd take if the deal breaks.

Reading the spread

For a cash deal, the spread is simple arithmetic:

$\text{spread} = \frac{P_{\text{deal}} - P_{\text{market}}}{P_{\text{market}}}$

Deal price minus current market price, as a percentage. With a $50 deal price and B trading at $48.50, the spread is $(50 - 48.50)/48.50 = 3.1\%$. If the deal is expected to close in four months, that 3.1% annualizes to roughly $3.1\% \times 3 = 9.3\%$ — a return that looks attractive next to cash, and that's the entire pitch for holding the position: buy B at $48.50, collect $50 when the deal closes, done.

Worked example — pricing in the probability. The market isn't pricing the spread off nothing; it's an implied probability. If a deal is genuinely certain to close, B should trade very close to $50, discounted only for the time value of money and financing cost — say $49.60 at typical short rates over four months. The observed $48.50 is 90 cents below that "certain-close" fair value, and that gap is compensation for deal risk. Suppose if the deal breaks, B falls back to its pre-announcement price of $40. Let $p$ be the market-implied probability the deal closes. Setting the expected value equal to the observed price:

$48.50 = p \times 50 + (1-p) \times 40$

Solving: $48.50 = 40 + 10p$, so $p = 0.85$. The market is pricing an 85% chance this deal closes. That's the number a merger arb desk is really underwriting — not "will this deal close," which is binary, but "is 85% too low, too high, or about right, given what I know about financing, antitrust posture, and shareholder approval."

Break risk is the whole risk

Notice the shape of that payoff: capped, modest upside if the deal closes; a large, uncapped-feeling downside if it breaks, because the stock doesn't just give back the spread — it falls back toward whatever it was worth as a standalone company, which is usually far below the deal price. This is why merger arb is sometimes described as picking up nickels in front of a bulldozer with a very predictable schedule: most positions make a small, steady amount, and occasionally one loses many times that amount in a single day when a deal collapses.

The main sources of break risk are: antitrust and regulatory rejection (the deal is blocked by competition authorities); financing failure (the acquirer's debt or equity financing falls through, common in leveraged deals); shareholder rejection (target or acquirer shareholders vote no); and a superior competing bid or MAC clause dispute (a "material adverse change" lets the acquirer walk, or a rival bidder appears and complicates the arithmetic). A skilled merger arb desk spends most of its research time handicapping these, deal by deal, rather than trading the spread mechanically.

Why deal risk isn't like normal market risk

The break risk in a single merger position is close to uncorrelated with the broader stock market on any given day — an antitrust ruling doesn't care what the S&P did that morning — which is the strategy's real diversification benefit and the reason merger arb funds report low market beta most of the time. But that benefit reverses exactly when it matters most: in systemic liquidity crunches (2008, March 2020), financing for pending deals dries up across the board simultaneously, so deal spreads across the entire book widen together as the market re-prices every pending deal's break risk upward at once, correlated risk showing up precisely in the environment where a fund most needed it not to.

In interviews

Be able to derive the implied break probability from the spread, break price, and deal price without hesitation — that's the standard "solve for p" question. Then explain the asymmetry explicitly: small, capped gain if the deal closes, large loss if it breaks, which is why position sizing and diversification across many uncorrelated deals matter more than getting any single deal's probability exactly right. Close with the correlation-in-a-crisis point — merger arb looks market-neutral until a systemic shock makes every deal's financing and antitrust risk move together.