How to Read Gamma Exposure (GEX)
Gamma exposure, or GEX, estimates how much option dealers may need to buy or sell the underlying asset as its price moves. Because those hedging flows can be large, GEX helps explain why some markets drift calmly inside a range while others accelerate sharply in one direction.
1. What gamma is
An option's delta measures how much its price changes when the underlying moves by one point. A call with a delta of 0.50 gains roughly 50 cents when the stock rises by a dollar. Delta is not constant, though. As the underlying moves, delta itself changes, and gamma is the rate of that change.
Gamma is highest for options that are at the money and close to expiration. A deep in-the-money or far out-of-the-money option has little gamma because its delta is already near 1 or 0 and barely changes. A same-day (0DTE) at-the-money option, by contrast, can see its delta swing from 0.2 to 0.8 within a small move, which means very high gamma.
2. Why dealer hedging matters
Market makers and dealers who take the other side of customer option trades generally do not want to bet on market direction. To stay neutral, they delta-hedge: they buy or sell the underlying (or its futures) so that their overall delta stays close to zero.
Because delta changes as price moves, the hedge has to be adjusted continuously, and gamma tells you how much adjusting is needed. When dealers hold a lot of gamma, every move in price forces a sizeable hedge trade. Aggregated across the whole market, those trades can be large enough to influence price behavior.
3. How GEX is calculated
For each option contract, GEX converts gamma into a dollar amount of hedging for a 1% move in the underlying:
The factor of 100 is the contract multiplier, and spot² × 0.01 converts gamma, which is measured per point, into dollars per 1% move. For example, suppose the S&P 500 index (SPX) is at 5,800 and a strike has 10,000 contracts of open interest with a gamma of 0.002. Then:
The direction comes from an assumption about who owns the options. The common convention, used on this site, is that dealers are long calls and short puts. The reasoning is that investors tend to sell calls (for example, covered calls for income) and buy puts (for protection), leaving dealers on the opposite side. Under that convention, call GEX is counted as positive and put GEX as negative, and the total net GEX is the sum across all strikes and expiries.
4. Positive and negative gamma regimes
The sign of net GEX describes how dealers are likely to hedge, and therefore how they may affect price.
| Positive net GEX | Negative net GEX | |
|---|---|---|
| Dealer position | Net long gamma | Net short gamma |
| When price rises | Dealers sell into strength | Dealers buy into strength |
| When price falls | Dealers buy into weakness | Dealers sell into weakness |
| Typical effect | Moves are dampened; price tends to mean-revert and realized volatility is often lower | Moves are amplified; trends can accelerate and realized volatility is often higher |
In a positive gamma regime, dealer hedging acts like a shock absorber: they lean against the move in both directions. In a negative gamma regime, hedging adds fuel: dealers have to chase the market, buying as it rises and selling as it falls. This is one reason sell-offs that start below key put-heavy strikes can feel disorderly, while markets sitting above large call positions often grind in narrow ranges.
A regime describes a tendency, not a forecast. Positive gamma does not mean the market cannot fall, and negative gamma does not mean it must crash. News, macro data and large flows can overwhelm dealer hedging at any time.
5. Key levels: gamma flip, call wall and put wall
Gamma flip
The gamma flip is the price at which total net GEX would change sign. It is found by recalculating total GEX as if the underlying were at a range of different prices and finding where the result crosses zero. Above the flip, dealers are estimated to be long gamma; below it, short gamma. Many traders watch the flip as a line between "calm" and "volatile" conditions. On this site, the GEX profile panel draws that recalculated curve directly.
Call wall
The call wall is the strike with the largest positive call GEX. As price approaches it, dealers hedging long calls sell more and more of the underlying, which can slow or cap a rally. Call walls often behave like resistance, especially into expiration, though a strong rally can push through and shift the wall higher.
Put wall
The put wall is the strike with the largest negative put GEX. It often marks an area where downside hedging flows are concentrated. Because put-heavy zones tend to sit in negative gamma territory, the put wall can act as support, but a decisive break below it can also accelerate selling.
6. Charm (CEX) and vanna (VEX) exposure
Gamma is not the only thing that changes dealer delta. Two other effects matter, particularly around expirations and volatility shocks.
Charm is the change in delta as time passes. As expiration approaches, out-of-the-money options lose delta and in-the-money options gain it, even if price does not move. CEX on this site shows how much dealer delta, in dollars, is expected to change over one day. A large positive CEX means dealers would need to sell that amount of the underlying as time passes; a negative value means they would need to buy. Charm flows are a common explanation for drift in the days leading into monthly options expiration.
Vanna is the change in delta when implied volatility changes. When implied volatility falls, for example after a feared event passes uneventfully, the deltas of out-of-the-money puts shrink, and dealers who were short those puts can buy back their short hedges, which supports price. VEX shows the change in dealer delta, in dollars, for a one-point rise in implied volatility. Both CEX and VEX use the same sign convention as GEX.
7. Reading the GEX page on this site
- Header metrics show total net GEX, CEX and VEX, the gamma flip, and the call and put walls. The badge next to the price tells you whether the market is currently in positive or negative gamma.
- Price chart overlays the key levels on recent price action, so you can see how price has behaved around them. Use the mouse wheel or drag to zoom the price axis, and double-click to reset.
- GEX by strike shows each strike's contribution. Switch between Net and Calls / Puts to see whether a level is driven by one side, and use the metric toggle to compare GEX, volume-based GEX, CEX, VEX and raw open interest.
- Expiry filter lets you isolate 0DTE, this week or this month. Short-dated options carry the most gamma, so near-term expiries often dominate intraday behavior, while longer-dated positioning matters more for multi-week levels.
- GEX profile recalculates total GEX across a range of hypothetical prices around spot. Where the curve crosses zero is the gamma flip.
8. Limitations you should know
- The positioning assumption can be wrong. Dealers are not always long calls and short puts. Large institutions sell puts, buy calls and trade complex spreads, and the true dealer position is not public.
- Open interest updates once a day. It reflects positions as of the previous session, so trades made today, including large 0DTE flows, are not captured. The volume-based GEX view is a rough way to see today's activity, but volume does not tell you whether positions were opened or closed.
- Data is delayed. Quotes on this site are delayed, so levels can shift during fast markets.
- Hedging is not the only flow. Fundamental news, macro releases, fund rebalancing and systematic strategies can overwhelm dealer hedging.
- Model assumptions. Greeks are computed with the Black-Scholes model using each contract's implied volatility, which is a simplification of how options are actually priced and hedged.
Used with those caveats in mind, GEX is best treated as a map of where hedging pressure is likely to be concentrated, rather than a signal to trade on its own.
Continue with VIX Term Structure Explained or Reading the Implied Volatility Surface.