GEX explained: what Gamma Exposure is and why it moves price

GEX (Gamma Exposure) is one of the most powerful tools for understanding why a stock or index gets "pinned" to a price or, instead, moves in a straight line. It doesn't measure what traders believe — it measures what market makers are forced to do to hedge their risk.

The idea in one sentence

When you buy an option, someone sells it to you — almost always a market maker. That market maker doesn't want to bet on direction, so they hedge by buying or selling the stock. Gamma measures how much they must adjust that hedge as price moves. The sum of all those hedges, by strike, is the GEX.

Positive vs negative gamma

• Positive gamma (GEX+): market makers buy when it drops and sell when it rises. This dampens the move and compresses the range — price tends to revert toward a level. Quiet, "sticky" days.
• Negative gamma (GEX−): market makers sell when it drops and buy when it rises. This amplifies the move — selloffs accelerate and rallies extend. Volatile days.

Three terms you'll hear

• Magnet node: the strike with the most concentrated gamma. Price tends to gravitate there, especially in positive gamma. A natural target.
• Flip zone (gamma flip): the price where GEX turns from positive to negative. Crossing it changes the regime: from "dampen" to "amplify".
• Walls: strikes with so much gamma they act as support or resistance until broken.

That's why GEX is so useful in 0DTE (options expiring the same day): gamma is huge near the price and defines whether the day will be range-bound or trending.

GEX is a map of probabilities, not a certainty. And in illiquid chains it loses reliability: a good reading flags that instead of faking precision.