The Complete Guide to Stock Merger Arbitrage and the Deal Spread
When one public company agrees to buy another, the target company's stock rarely jumps straight to the offer price. It settles a little below, and that small gap is an opportunity. Merger arbitrage, also called risk arbitrage, is the strategy of buying the target stock at the discounted market price and collecting the full offer price when the deal closes. This guide explains the math behind the calculator above, how to read the annualized return, and the risks that make this strategy anything but free money.
How to Use This Merger Arbitrage Calculator
Enter your Total Investment Capital, which is the amount of cash you plan to put into the target stock. Enter the Current Market Price per Share, the price the stock trades at today, and the Official Acquisition Offer Price per Share, the amount the buyer has agreed to pay at closing. Finally, set the Expected Days Until Deal Closes, either by typing a number or tapping one of the quick-select buttons for three months, six months, or one year. Everything recalculates instantly as you type, with no submit button. By default the tool allows exact fractional shares for precise math, but you can flip the Whole Shares Only toggle to round down to whole shares the way most brokerage orders actually fill.
The Merger Arbitrage Math, Step by Step
The engine first divides your capital by the current market price to find how many shares you can buy. The raw deal spread is simply the offer price minus the market price, the profit per share if the deal closes. Multiplying your share count by the offer price gives the gross payout you receive at closing, and subtracting your original capital leaves your net profit. Dividing that net profit by your capital and multiplying by 100 gives the absolute return as a percent. The final and most important step annualizes that figure: it multiplies the absolute return by 365 divided by the expected days to close, scaling the result up to a full-year equivalent so you can compare it against a savings account or any other investment.
A Worked Example
Suppose you invest 5,000 dollars in a target stock trading at 47.50 per share while the buyout offer is 50.00 per share, with the deal expected to close in 120 days. Your capital buys about 105.26 shares. The raw spread is 2.50 per share. At closing your 105.26 shares pay out the offer price for a gross payout of about 5,263.16 dollars, leaving roughly 263.16 dollars in net profit. That is an absolute return of about 5.26 percent. Because the money was only tied up for 120 days, annualizing it by multiplying by 365 over 120 produces an annualized return of about 16 percent, far better than a typical 5 percent savings account, which is exactly why arbitrageurs chase these spreads.
Why the Annualized Return Matters More Than Raw Profit
A 263 dollar profit sounds modest, and on its own it does not tell you whether the trade was worth it. The annualized return puts every deal on equal footing by accounting for how long your capital is locked up. The same 5.26 percent earned over four months is excellent, but stretched over two years it would be mediocre and not worth the deal risk. Always compare a merger's annualized return against the risk-free alternatives available to you. If a deal only annualizes to a few percent, the small reward rarely justifies the chance that the merger collapses.
The Risk That Makes This Risk Arbitrage
The spread exists for a reason: deals can and do break. Antitrust regulators may sue to block a merger, target shareholders may vote it down, financing may evaporate, or the buyer may simply walk away and pay a breakup fee. When that happens the takeover premium vanishes and the target stock usually falls hard, often below where it traded before the deal was announced. That downside is typically much larger than the spread you stood to earn, so position sizing and an honest read of each deal's regulatory odds matter far more than the headline annualized number. This calculator assumes the deal closes at the stated offer price on schedule; it does not price in the probability of failure, which is the single most important judgment you bring to the trade.