What is Gamma Exposure (GEX)? Definition, Formula, and Example
Gamma exposure (GEX) is the aggregate gamma position of options dealers across all listed strikes on an underlying, expressed in dollars of share-buying or selling required per 1% move.
What Is Gamma Exposure?
Gamma exposure (GEX) measures the cumulative gamma position that options market makers hold across every strike and expiration on a given underlying. Because dealers run a delta-neutral book, their gamma position dictates how many shares they must buy or sell as the underlying moves to stay hedged. GEX is reported in dollars per 1% (or per 1-point) move and tells traders whether dealer hedging will dampen volatility (positive GEX) or amplify it (negative GEX). It is one of the most-watched flow metrics on Tapeboard's options dashboards and a core input for regime-aware traders.
How Gamma Exposure Is Calculated
For a single option contract, dollar gamma is:
$Gamma = Γ × Open Interest × 100 × S² × 0.01
where Γ is the option's gamma, S is the spot price, and the 0.01 scales to a 1% move. Net GEX aggregates across the chain assuming dealers are short calls and long puts (the dominant retail-flow assumption):
Net GEX = Σ (Γ_call × OI_call) − Σ (Γ_put × OI_put), scaled by spot² × 0.01.
Positive net GEX → dealers buy when price falls and sell when it rises (mean-reverting). Negative net GEX → dealers sell into weakness and buy into strength (trend-amplifying). The crossover point is the gamma flip level, often the most important strike on the board.
Worked Example: SPY Gamma Exposure
On May 5, 2026, SPY trades at $520. The 520-strike calls expiring in 14 days carry gamma of 0.038 with 62,000 contracts of open interest:
Dollar gamma = 0.038 × 62,000 × 100 × 520² × 0.01 = $6.37 million per 1% move at that single strike.
If the full SPY chain aggregates to a net GEX of +$2.1 billion, dealers must sell roughly $2.1B of SPY-equivalent stock for every 1% rally and buy $2.1B for every 1% drop. That hedging flow compresses realized volatility. If the same chain prints −$1.5B GEX after a put-buying wave, dealers must sell into drops — a setup that often precedes accelerated downside and an expanding VIX.
When Traders Use GEX
GEX has three primary uses. First, regime identification: positive-GEX days favor mean-reverting intraday strategies (fade extremes, sell straddles); negative-GEX days favor trend-following and breakout plays. Second, gamma flip mapping: the strike where net GEX crosses zero is a gravitational pivot — markets pin to it on expiration days. Third, squeeze setup detection: when call gamma builds at out-of-the-money strikes and price approaches them, dealer hedging buys can fuel a gamma squeeze.
Limitations and Misconceptions
GEX is an estimate, not a measurement. Dealer positioning is not publicly disclosed; the standard "dealers short calls, long puts" assumption breaks during periods of heavy institutional call buying or covered-call ETF growth (JEPI, QYLD, XYLD flows), which can flip dealers long calls. GEX only counts listed options — bilateral OTC structures and structured products carry their own dealer hedges that never appear in the data. The metric tells you the *amount* of hedging flow per 1% move, not the *direction the market will take*; a negative GEX regime is more volatile but not inherently bearish. Finally, GEX models ignore second-order Greeks like vanna and charm, which drive significant flow into and out of expiration.