M&A and arbitrage spreads

When one company agrees to buy another, the target's stock stops trading on its own fundamentals and starts trading on one question: will the deal close, and when? The gap between the market price and the offer price is called the arbitrage spread, and reading it is a skill that applies far beyond merger arbitrage itself.

The announcement

A deal announcement contains the terms a trader needs:

• Offer price and form. Cash ($50 a share), stock (0.8 shares of the acquirer per target share), or a mix.
• Premium. The offer versus the target's price before the announcement. Typically 20% to 40%.
• Conditions. Shareholder votes, regulatory approvals (antitrust, foreign investment), financing.
• Expected closing. Usually a quarter to a year out.
• Break fee. What the acquirer pays if it walks; what the target pays if it accepts a better offer.

The target gaps up on the announcement to somewhere close to, but below, the offer. The acquirer often falls, because it is paying a premium and taking on risk.

Reading the spread

Suppose an acquirer agrees to buy ACME for $48 a share in cash, a 20% premium to the $40 pre-announcement price, with closing expected in nine months. ACME opens at $46.

Spread = $48 − $46 = $2.00, or $2.00 ÷ $46 = 4.3% gross.

Annualised: 4.3% × (12 ÷ 9) = 5.8%.

That annualised number is what the market is charging for the risk that the deal fails plus the time value of money. Compare it with the risk-free rate. If Treasury bills yield 4.5%, the spread offers about 1.3 percentage points of extra return for taking deal risk. That is a "normal" spread for a clean cash deal with low regulatory risk.

Now the spread tells you what the market thinks. A rough way to back out the implied probability of the deal closing:

If the deal closes: ACME goes to $48. If it breaks: ACME probably falls back toward $40 (perhaps lower, since a failed deal can damage the target).

Let p be the probability of closing. The expected price is p × $48 + (1 − p) × $40 = $46 (ignoring time value for simplicity).

48p + 40 − 40p = 46, so 8p = 6, and p = 0.75.

The market is pricing roughly a 75% chance of closing on this simplified view. With time value added back, a little higher. A spread that widens to $4 (price $44) implies p = 0.5; the market has become worried. A spread that narrows to $0.50 implies near-certainty.

Key idea: The arbitrage spread is a live vote on whether a deal closes. Spread = offer − price; the implied probability of closing falls out of the spread and the likely price if the deal breaks.

Stock deals

If the offer is 0.8 acquirer shares per ACME share and the acquirer trades at $60, the offer is worth $48, but that value moves with the acquirer's stock every day. Arbitrageurs buy the target and short 0.8 shares of the acquirer per target share to lock in the spread. For a trader who is simply long the target, a stock deal means you are now effectively long the acquirer; if the acquirer drops 15%, so does your "guaranteed" $48.

Many stock deals have a collar, a range within which the exchange ratio adjusts to keep the value fixed. Read the terms.

Why spreads widen

The spread is not a free 5.8%. It widens, sometimes violently, when:

• Regulators object. Antitrust reviews, especially for deals that reduce competition, can take a year and end in a lawsuit. The spread often goes from 4% to 15% on the first sign of a second request for information.
• Financing wobbles. A leveraged buyer in a rising-rate environment may struggle to place the debt.
• The acquirer's stock falls sharply (stock deals), or the acquirer's own business deteriorates and it looks for a way out.
• A material adverse change is claimed. Rare, litigated, but real.
• The target's shareholders revolt. They may vote no if they think the price is too low, especially if a rival bid seems possible.

When a deal breaks, the target usually falls to at least its pre-deal price, and often below, because the market now knows it was for sale and nobody else paid up. A "safe" 4% spread position can lose 15% in a morning.

The upside surprise is a second bidder. If ACME trades above the offer ($48.50 against $48), the market is pricing in the chance of a topping bid.

What a swing trader does with M&A

Most swing traders do not run merger arbitrage; it needs scale and low financing costs. But deal knowledge matters in four places:

1. A position in a target. Once the deal is announced, the stock is dead money unless a topping bid arrives. Most traders take the gap and leave.
2. A position in the acquirer. Acquirers often fall on the announcement and sometimes keep falling if the deal is large, dilutive or debt-funded. Check how much goodwill will be created and what debt/EBITDA becomes.
3. Sector reads. A deal in a sector re-rates its peers: if ACME is bought at 14 times EBITDA, other industrials at 10 times get looked at. Peer stocks often rally on the announcement day.
4. Avoiding the short. Never short a stock that trades like a takeover target (unusual volume, sector consolidation, activist filings) without a specific reason. The gap up on an announcement is 20% to 40%.

A worked scenario

Three months into the ACME deal, the antitrust regulator issues a second request. ACME drops from $46.50 to $43. Spread is now $5 (11.6% gross). The likely break price is around $38 (the sector has fallen since). Implied p = (43 − 38) ÷ (48 − 38) = 0.5.

A trader with no position and no view on the regulatory outcome should recognise this as a 50/50 bet with +$5 / −$5 outcomes, minus time. Not a trade without an edge. A trader long from $46 must decide whether to take the $3.50 loss or hold a coin flip. Most take the loss; the position no longer has a defined risk.

Try it: Find any announced cash deal (business news lists them daily). Compute the gross spread, the annualised spread, and, using the pre-deal price as the break price, the implied probability of closing. Then read the press release for the conditions and see whether the market's probability seems high or low to you.

Recap

• The target gaps to just below the offer; the gap is the arbitrage spread, which pays for deal risk and time.
• Implied probability of closing = (price − break price) ÷ (offer − break price), a rough but useful read.
• Stock deals expose you to the acquirer's share price; check for collars.
• Spreads widen on regulatory objections, financing trouble and acquirer weakness; a broken deal takes the target below its pre-deal price.
• Swing traders use M&A mainly to exit targets, judge acquirers, read sector re-ratings, and avoid shorting likely targets.