What Is Gamma Exposure (GEX)? Dealer Gamma Explained
Gamma exposure, usually shortened to GEX, is the single most useful number for understanding why a stock behaves calmly on one day and violently on the next.
What is gamma exposure (GEX)?
Gamma exposure, or GEX, estimates how many shares options dealers must buy or sell to stay hedged when the underlying moves one point. Positive gamma exposure means dealer hedging dampens price movement. Negative gamma exposure means dealer hedging amplifies price movement, which is why negative gamma sessions trend harder.
Every option a dealer sells creates an ongoing hedging obligation. As the underlying price moves, the delta of that option changes, and the rate of that change is gamma. The dealer must trade the underlying to stay flat, and the direction of that forced trading is what gamma exposure measures in aggregate across every strike.
How is gamma exposure calculated?
Gamma exposure per strike multiplies the option gamma by open interest, by contract multiplier, and by the square of spot price, then flips the sign for puts under the standard dealer convention. Summing every strike produces net gamma exposure for the whole underlying at that moment.
The sign convention matters and is where two tools most often disagree. The common assumption is that dealers are long calls and short puts against retail flow, so call gamma carries a positive sign and put gamma a negative one. That assumption is a convention rather than a measurement, because actual dealer inventory is never published.
What does positive gamma exposure mean?
Positive gamma exposure means dealers hedge against the prevailing move, selling into strength and buying into weakness. Positive gamma compresses realised volatility, pins price near heavy strikes, and favours mean reversion. Ranges tend to hold and breakouts tend to fail during a positive gamma session.
What does negative gamma exposure mean?
Negative gamma exposure means dealers hedge in the same direction as the move, selling into weakness and buying into strength. Negative gamma amplifies realised volatility and produces trending, gap prone sessions. Stops get run more often and breakouts follow through more reliably during negative gamma.
Frequently asked questions
Is high gamma exposure bullish or bearish?
Gamma exposure is directionally neutral. Gamma exposure describes how price is likely to behave, meaning calm or volatile, rather than which direction price will take.
Does gamma exposure work on every ticker?
Gamma exposure is most reliable on underlyings with deep, liquid option chains. On a thinly traded name the open interest is too small for dealer hedging to meaningfully move the underlying.
How often does gamma exposure change?
The open interest component updates once daily, but the spot and gamma components move continuously through the session, so the exposure profile shifts in real time as price travels.