Gamma Exposure (GEX) is the dollar amount that a market maker's net delta changes for every one-point move in the underlying. It is computed per strike and summed across the chain to produce an aggregate figure that describes the entire dealer book.
When aggregate GEX is positive, dealers are long gamma and must trade against the move to stay delta-neutral — buying dips and selling rips. This creates the pinning, mean-reverting behavior that characterizes positive-gamma sessions. When aggregate GEX is negative, dealers are short gamma and must trade with the move, amplifying trends and producing the volatile, trending sessions traders associate with selloffs.
How GEX is calculated
For each option, gamma exposure equals the option's gamma multiplied by open interest, the contract multiplier (100 for equity options), and the underlying price squared. Calls are conventionally treated as long-gamma for the dealer-short side; puts as short-gamma. Sum across all strikes and expirations to get aggregate GEX.
ChartGEX computes a strike-level gamma profile from the full options chain (CBOE-sourced, 15-minute refresh), then displays GEX by DTE so traders can see whether near-dated or longer-dated hedging is dominant.
GEX_strike = Γ × OI × 100 × S²Why it matters
GEX is the single highest-signal-to-noise metric for reading modern equity-index price action. It tells you what regime you are in (mean-reverting vs. trending), where dealers are forced to act (the call wall and put wall), and where the regime flips (the gamma flip). Used correctly, it converts random-looking intraday moves into structurally backed setups.