You set a stop loss on option expiry day, and the moment price touches it, your order is filled. Looking back, if your stop had been just a few points wider, the trade might have recovered and even made money. That frustrating feeling of being shaken out is often directly linked to a sudden rise in Gamma.
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On option expiry day, Gamma increases sharply. This means even a small move in the underlying price can cause a large jump in the option price, making your stop loss much easier to trigger.
Step 1: Understand Gamma's "Amplifier" Effect
Gamma measures how much Delta changes when the underlying price moves. In simple terms, Delta is how sensitive the option price is to changes in the underlying asset price, while Gamma is the speed at which that sensitivity changes.
Think of it like driving: Delta is your speed, and Gamma is your acceleration.
As options approach expiry, especially at-the-money options, Gamma increases sharply. This leads to two results:
- Even a tiny move in the underlying asset can cause Delta to change quickly.
- The option price becomes much more sensitive to movements in the underlying asset.
Step 2: Why Stop Losses Are Triggered More Easily on Expiry Day
Based on the logic above, here is what happens on expiry day:
- At-the-money options have the highest Gamma: When price moves near the strike price, Gamma is at its highest. Even a move of a few dozen dollars can make the option price jump by several percentage points.
- Price moves faster: Because of Gamma's amplifying effect, a tiny move in the underlying asset can turn into a large change in the option price. A stop loss level that is normally safe might be pierced by a single 15-minute candle on expiry day.
- Liquidity may thin out: Near the close, some traders have already closed their positions. There may be fewer bids and offers, making sharp wicks more likely.
One key difference: Buyers and sellers face completely different risks on expiry day. Buyers hold positive Gamma, meaning gains accelerate when price moves in their favor. Sellers, however, hold negative Gamma, meaning losses accelerate when price moves against them. This is also clearly noted by the Shenzhen Stock Exchange: as an option contract approaches expiry, the Gamma of short positions gradually increases, making risk hedging more difficult for the seller.
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Step 3: How to Deal with This "Gamma Trap"
If you do not want to be repeatedly stopped out by the Gamma effect on expiry day, keep these points in mind:
Idea 1: Do not use your usual stop loss distance
One to two days before expiry, consider widening your stop loss to leave room for Gamma-driven price jumps. If you are unwilling to widen your stop, consider rolling your position to next month's contract in advance to avoid the window where Gamma spikes sharply.
Idea 2: Distinguish between a real breakout and Gamma noise
Sharp rallies or drops on expiry afternoon are partly mechanical moves caused by hedging flows and Gamma squeeze. They do not necessarily represent a new trend direction. When making judgments, you can filter signals using volume changes and the distribution of option strike prices.
Idea 3: Sellers should pay special attention to margin changes
If you sold options, rising Gamma on expiry day means Delta is changing quickly, and maintenance margin may increase at any time. Avoid trading at full margin. Leave enough room to handle potential margin calls.
Checklist before expiry: If you plan to hold an option to expiry, evaluate at least 24 hours in advance whether to close the position or roll it to next month. If you choose to keep holding, adjust your stop loss to an "expiry day mode" that is at least somewhat wider than usual, so you do not get shaken out by Gamma noise.
