The short box is an arbitrage strategy that involves selling a bull call spread together with the corresponding bear put spread with the same strike prices and expiration dates. The short box is a strategy that is used when the spreads are overpriced with respect to their combined expiration value.
Sell 1 call at the lower strike price; Buy 1 call at the higher strike price; Buy 1 put at the lower strike price; Sell 1 put at the higher strike price. Use the same expiration date.
Matched payoff and financing considerations
The combined expiration payoff can be fixed under matched contract assumptions. That is not a guarantee of risk-free profit: financing, stock borrow, dividends, early assignment, execution and settlement must also be considered. American-style box spreads can be disrupted by early exercise. A price difference alone does not establish an executable arbitrage.
The matched box’s expiration cashflow magnitude is the higher strike minus the lower strike, times the contract multiplier. A short box owes this amount; a long box receives it.
For the stated strikes, the expiration obligation is ($60 − $50) × 100 = $1,000. The original $50 − $40 expression used the wrong strikes despite giving the same width.
Example
Suppose XYZ stock is trading at $55 in July and the following prices are available:
- AUG 50 put - $2
- AUG 60 put - $7
- AUG 50 call - $7
- AUG 60 call - $1.50
Selling the bull call spread involves shorting the AUG 50 call for $700 while buying the AUG 60 call for $150. The premiums collected from the sale of the bull call spread is: $700 - $150 = $550
Selling the bear put spread involves shorting the AUG 60 put for $700 while buying the AUG 50 put for $200. The premiums collected from the sale of the bear put spread comes to: $700 - $200 = $500
Together, the net premium received for shorting the box is: $550 + $500 = $1050
If XYZ remain unchanged at $55, then the AUG 50 put and the AUG 60 call expire worthless while both the AUG 50 call and the AUG 60 put expires in-the-money with $500 intrinsic value each. So the total value of the box at expiration is: $500 + $500 = $1000.
Suppose, on expiration in August, XYZ stock rallies to $60, then only the AUG 50 call expires in-the-money with $1000 in intrinsic value. So the box is still worth $1000 at expiration.
So what happens when XYZ stock plunges to $50? A similar situation occurs but this time it is the AUG 60 put that expires in-the-money with $1000 in intrinsic value while all the other options expire worthless. Hence, the box is still worth $1000.
The $1,050 entry credit less the $1,000 matched expiration obligation leaves $50 before financing and costs. This is not a guaranteed executable closing price or risk-free financing rate.
These examples use standard U.S. stock options with a 100-share contract size and matching expiration dates. Related structures can use ETF, index or futures options, but contract multipliers, exercise style, settlement and the underlying price range can differ. A stock’s zero price floor must not be assumed for every futures contract.
Commissions
As the gains from the short box is very minimal, the commissions payable when implementing this strategy can often wipe out all of the profits. Thus, one have to take into careful consideration the commissions involved when contemplating the use of this strategy.
For active traders, transaction costs can consume a significant part of returns. Compare the full commission and fee schedule, exercise and assignment charges, and bid-ask spreads. The cost of entering and closing every leg matters.
Long Box
The short box is profitable when the component spreads are overpriced. When the spreads are underpriced, the converse strategy known as the long box, or simply box spread, is used instead.
Before expiration and assignment
The diagrams and worked outcomes describe expiration payoffs, not an option’s market price before expiration. Time decay, implied volatility, rates, dividends and bid-ask spreads affect early closing values. American-style short options can be assigned early; a protective long option is not automatically exercised when a short leg is assigned. Closing or exercising one leg can change the remaining position’s risk.
Payoff summary
Maximum profit: Lower strike price minus higher strike price minus net opening cost.
Maximum loss: Higher strike price plus net opening cost minus lower strike price.
Breakeven
The position breaks even at every stock price only when the net opening cost equals lower strike price minus higher strike price. Otherwise, there is no breakeven stock price.
Net opening cost means everything paid to open the position, less everything received. Include the shares as well as the options. If opening the position brings in money overall, treat that cost as a negative amount.
Amounts are per share before fees. Multiply by the shares covered by the position; standard equity options usually cover 100 shares per contract. If a maximum profit or loss calculation gives a negative amount, use zero. These figures assume matching contracts held to expiration and do not include financing or early assignment.
Financial mechanics reviewed:
Sources: OIC strategy reference; OIC assignment guidance. Formulas use the stated payoff assumptions; examples are illustrative, not market quotes. Editorial standards and corrections.