Gamma Exposure (GEX)
// dollar-gamma of all open option contracts, signed by dealer position
Gamma Exposure (GEX) is the dollar-gamma of all open option contracts on a given underlying, signed by the dealer's presumed position. It is published in dollars per 1% move in the underlying.
- Aggregate dealer-position gamma across an option chain. Positive GEX implies dealers buy dips and sell rips (volatility-suppressive); negative GEX implies the reverse (volatility-amplifying).
- Tapeboard computes GEX from CBOE end-of-day open interest and a Black-Scholes second derivative for gamma, summed across the active chain.
- Dealer position is not publicly observable. GEX assumes the standard retail-flow posture (dealers short calls, long puts) and surfaces the assumption rather than presenting it as fact.
How it is calculated
Gamma is the second derivative of option price with respect to spot. Multiplying by open interest and by 100 (contract multiplier) gives raw gamma exposure; multiplying by spot squared converts to dollars per 1% move. The dealer-sign mask flips call gamma negative on the assumption that the dealer is the short side of retail call buying.
What traders use it for
- Identifying the strike at which dealer hedging flows flip from supply to demand. The "gamma flip" level is where aggregate GEX crosses zero, often a magnet for price action.
- Estimating intraday volatility regime. Sustained negative GEX days run hotter than positive GEX days because dealer hedging amplifies moves.
- Sizing positions around large open-interest strikes. Strikes with disproportionate gamma exposure pin price action through expiration.
Worked example
Suppose $SPY trades at $507 and the next monthly expiry has 1.2M call contracts of open interest at the $510 strike with a per-contract gamma of 0.038. Raw gamma at the strike is 1,200,000 * 0.038 * 100 = 4,560,000. Multiplying by spot squared and the call dealer-sign of -1 gives a GEX contribution of about -$1.17B per 1% move in SPY. Sum across all strikes to get the chain GEX. As of 2026-05-02 16:00 ET, the SPY chain printed positive aggregate GEX, consistent with a low-VIX print of 14.2.
Live data: /stocks/SPY.
Common pitfalls
- Dealer positioning is not observable. The dealer-sign mask is an assumption, not a fact. A high-conviction GEX read can be wrong because retail or institutional flow flipped the standard posture.
- Intraday GEX is an estimate. Tapeboard interpolates against the morning open-interest snapshot and rebuilds end-of-day from settled OI. Real-time GEX from any vendor is interpolation, not measurement.
- GEX ignores vanna and charm. Gamma is one greek; vanna (sensitivity to vol) and charm (sensitivity to time) move dealer hedges too. A GEX-only view misses the vol-sensitive component of dealer flow.
- Single-name GEX is noisier than index GEX. Index GEX aggregates across a deep, liquid chain; single-name GEX can swing on one large block trade.
Where this metric appears on Tapeboard
GEX appears on every `/stocks/{T}/options` page (per-strike and aggregate), on the GEX leaderboard at /gex, and as a screener filter on /scanner. Index GEX for $SPY and $QQQ renders on the daily Tape Open commentary.
Tapeboard surfaces this metric as a first-class screening filter. See the comparison pages at all Bloomberg alternatives for how Tapeboard's gamma exposure (gex) surface compares against Koyfin, Finviz, TradingView, and Unusual Whales.
Related terms
- Gamma Ramp: Plot of GEX (y-axis) vs hypothetical spot prices (x-axis). The zero-crossing is the "gamma flip" level.
- IV Rank: Range-based, not percentile-based. IV Rank uses the highest and lowest IV prints over the lookback; IV Percentile counts the share of days below current.
- Options Flow: OPRA is the consolidated US options price-reporting authority; every executed options trade reports to OPRA in real time.
- Squeeze Score: Five-input composite: SI %-of-float (35%), borrow fee (25%), float utilization (20%), days to cover (15%), 5-day momentum (5%). Weights last calibrated 2024-11-15.
Primary sources cited
- CBOE Options Open Interest documentation: GEX inputs (open interest, strike, expiry) are sourced from CBOE-published end-of-day option data. https://www.cboe.com/us/options/market_statistics/historical_data/, retrieved 2026-05-04.
- OPRA (Options Price Reporting Authority): OPRA is the consolidated US options price-reporting authority. https://www.opraplan.com/, retrieved 2026-05-04.
Methodology last reviewed 2026-05-04 by Marcus Reilly, Editor at Tapeboard. Every claim on this page has a row in the citation registry. Glossary terms reverify on the Jan 15 / Apr 15 / Jul 15 / Oct 15 cron and any time the underlying primary-source publishes a methodology change. See methodology for the full fact-check process and corrections for the public correction log.
Disclaimer. This page is for educational and informational purposes only. Nothing on Tapeboard is investment advice. See the full risk disclaimer.