Gamma Exposure (GEX), Spot GEX & the Gamma Flip

Gamma Exposure (GEX) estimates how much hedging market makers must do as the underlying moves, and therefore whether dealer activity is likely to dampen or amplify price swings. It is the most-watched of Unusual Whales' Greek Exposure metrics. The core idea: dealers who are net short options must continuously buy and sell the underlying to stay delta-neutral, and the direction of that forced hedging flips depending on whether their net gamma is positive or negative.

What GEX measures and why dealers hedge

Unusual Whales frames it precisely: "Greek Exposure is the assumed greek exposure that market makers are exposed to. The most popular greek exposure is gamma exposure (GEX)." The model assumes dealers are on the other side of most retail and institutional flow — that "the bulk of their transactions are buying calls and selling puts to investors hedging their portfolios." Because dealers profit from the bid-ask spread, not from directional bets, they "constantly gamma hedge (they buy and sell shares to keep their positions delta neutral)." GEX sums each contract's gamma across all open interest to estimate the total share-hedging dealers face.

The exposure math UW uses

Per UW, "if a market maker has one contract open with a gamma value of 0.05, then that market maker is exposed to 0.05 * [100 shares] of gamma," and total exposure is the sum across all open contracts weighted by daily open interest. UW's OpenAPI spec gives the call/put aggregates explicitly: GEX call gamma is "the sum of the gamma values of all call transactions that executed multiplied by the open interest and the number of shares per contract (typically 100 shares per contract)," with put gamma the analogous sum (and reported as negative). UW also reports the dollar hedging per 1% move two ways: by open interest (gamma * open interest * price * price) and by volume (gamma * volume * price * price).

Positive vs negative gamma regimes

The regime determines whether dealers buy into strength or sell into it. UW: "Long call positions are positive gamma — as the stock price increases and delta rises (approaches 1), market makers hedge by selling shares, and they buy shares if the stock price decreases." That is stabilizing: dealers sell rallies and buy dips. Conversely, "Short put positions are negative gamma — as the stock price increases and delta falls (approaches −1), market makers hedge by buying shares, and they sell shares if the stock price decreases." That is destabilizing: dealers chase the move. The net of all positions across all strikes determines which force dominates.

Why positive gamma pins and negative gamma accelerates

UW states the consequence directly: "in the event of large positive gamma, volatility is suppressed as market makers will hedge by buying as the stock price decreases and selling as the stock price increases. And in the event of large negative gamma, volatility is amplified as market makers will hedge by buying as the stock price increases and selling as the stock price decreases." In a positive-gamma regime the dealer hedging is mean-reverting — it pushes price back toward heavily-traded strikes, producing the "pinning" effect into expiration. In a negative-gamma regime the hedging is trend-following — it pours fuel on moves, which is why down days in negative-gamma environments can cascade.

Spot GEX

Spot GEX is the same idea expressed in dollars at the current price. UW: "Spot GEX is the assumed $ value of the given greek (ie. gamma) exposure that market makers need to hedge per 1% change of the underlying stock's price movement. A positive value is long and a negative value is short." For a single contract the spot exposure is 0.05 * 100 shares * 0.01 * stock price * (the underlying parameter of the greek — for gamma, the stock price), summed across all open contracts by open interest or by volume, and reported per minute. Spot GEX tells you, in real dollars, how many shares dealers must trade for the next 1% move — large positive spot GEX means a strong stabilizing cushion; large negative spot GEX means an unstable, move-amplifying tape.

The gamma flip / zero-gamma level

The gamma flip (or zero-gamma level) is the underlying price at which net dealer gamma crosses from positive to negative. Above it, dealers are net long gamma and their hedging suppresses volatility; below it, they are net short gamma and their hedging amplifies volatility. The flip level therefore acts like a volatility regime boundary: trading above zero-gamma tends to be calm and range-bound, while a break below it can usher in fast, trending, high-volatility conditions. Watching where price sits relative to the flip — and how the flip itself migrates as positioning changes — is a primary use of GEX data.

How UW lets you slice it, and the caveats

UW exposes Greek Exposure by strike, by expiry, and by strike-and-expiry, plus spot GEX per minute and by strike/expiry, so you can see exactly where the gamma is concentrated. High-gamma strikes act as magnets and as support/resistance because that is where dealer hedging is most intense. The caveats: GEX rests on the assumption about which side dealers take (buy calls / sell puts to hedgers), so it is a well-reasoned estimate, not measured positioning. It also assumes dealers actually delta-hedge mechanically, which is mostly but not perfectly true. Read GEX as a map of where forced hedging is likely, then confirm with price action rather than trading the level blindly.