Reversal Arbitrage: The Mirror of a Conversion

Key Takeaways

• Reversal arbitrage shorts stock plus a long call and short put at one strike and date.
• It captures a parity violation when the put is rich relative to the call.
• The locked payoff is fixed and direction-neutral once the trade is on.
• Short-sale borrow costs and hard-to-borrow fees are the main drag on the edge.

What It Is

A reversal, or reverse conversion, pairs a short stock position with a synthetic long stock built from options: a long call and a short put at the same strike and expiration. The synthetic long cancels the price risk of the short shares.

The remaining payoff is fixed by the strike and the option prices. Reversal arbitrage uses this to exploit a put-call parity violation in the opposite direction from a conversion. When the put is too expensive relative to the call, the reversal locks the gap.

The Intuition

Put-call parity links a synthetic long (long call plus short put) to a financed long stock position. If the put is overpriced, the synthetic long is cheap relative to the stock, so you want to buy the synthetic and sell the stock short.

That is the reversal. You buy the cheap call, sell the rich put, and short the shares to remove direction. The short stock and synthetic long net out, so price moves do not matter. You collect the mispricing as a fixed amount.

How Reversal Arbitrage Options Trades Work

The legs and the parity condition:

Reversal = short stock + long call + short put   (same K, same expiration)

Put-call parity (no dividends):
  C - P = S - K * e^(-rT)

Reversal profits when the put is rich:
  C - P  <  S - K * e^(-rT)

At expiration you receive the strike either way. If the stock is above the strike, you exercise the long call and buy shares at the strike to close the short. If below, the short put is assigned and you buy shares at the strike to close the short. The outcome was fixed at entry, so the profit is the parity gap minus borrow costs, carry, and commissions.

Worked Example

A stock trades at 50. The 50-strike put trades at 2.30 and the 50-strike call at 2.00, same near-term expiration. Assume small carry and no dividend.

The put is 0.30 richer than parity allows. You build the reversal: short 100 shares at 50, buy the 50 call for 2.00, sell the 50 put for 2.30. The net option credit is 0.30.

If the stock finishes at 55, you exercise the call and buy shares at 50 to cover the short; the put expires worthless. If it finishes at 45, the short put is assigned and you buy at 50 to cover; the call expires worthless. Either way you close the short at the strike and keep the 0.30 credit, locking about 30 dollars per contract before costs. The catch specific to reversals: you must borrow shares to short, and the borrow fee reduces the edge. If the stock is hard to borrow, that fee can wipe out the profit entirely.

Common Mistakes

1. Ignoring borrow costs. The short leg requires borrowing shares. Hard-to-borrow fees can exceed the parity edge, turning a "locked" profit into a loss.

2. Forgetting dividends on the short. If you are short the stock over an ex-dividend date, you owe the dividend. That payment can erase the trade's profit.

3. Overlooking early assignment. An American short put deep in the money can be assigned early, forcing you to buy shares before you planned and unwinding the hedge.

4. Assuming locate and execution are free. Three legs plus a short sale mean multiple spreads, commissions, and a share locate. The thin edge rarely survives sloppy execution.

5. Confusing reversal with conversion. A reversal shorts stock when the put is rich. A conversion holds long stock when the call is rich. Swapping them reverses your exposure.

Frequently Asked Questions

What is reversal arbitrage in options trading in simple terms? Reversal arbitrage options trades short the stock and pair it with a long call and short put at one strike to capture a pricing error. When the put is too expensive next to the call, the trade locks a small fixed profit regardless of direction.

How does reversal arbitrage affect investment decisions? It is a market-neutral way to capture a put-call parity violation rather than a directional trade. In the worked example, a 0.30 parity gap produced about 30 dollars of locked profit per contract before borrow costs.

What is a real-world example of reversal arbitrage? A market maker sees a 50-strike put trading richer than parity allows, sells the put, buys the matching call, and shorts the stock, banking the gap while borrow and carry costs decide the net edge.

How can investors avoid losing money on reversal arbitrage? Check the borrow fee and dividend schedule before trading, since both fall on the short stock leg, and confirm the parity edge survives commissions, spreads, and the share locate.

How is reversal arbitrage different from conversion arbitrage? A reversal shorts stock with a long call and short put when the put is overpriced. A conversion holds long stock with a long put and short call when the call is overpriced. They are exact mirror images.

Sources

1. OIC (The Options Industry Council). "Put/Call Parity." https://www.optionseducation.org/advancedconcepts/put-call-parity
2. Damodaran, A. (NYU Stern). "Options Arbitrage." https://pages.stern.nyu.edu/~adamodar/New_Home_Page/invfables/optionarb.htm
3. Corporate Finance Institute. "Put-Call Parity." https://corporatefinanceinstitute.com/resources/derivatives/put-call-parity/
4. Cboe Options Institute. "Options Education and Strategy Resources." https://www.cboe.com/optionsinstitute/

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.