Is GEX the same as gamma?

Gamma is a property of one option: how fast its delta changes as the stock moves. GEX, gamma exposure, is the sum of gamma across all open contracts in a name, weighted by open interest and signed by who is assumed to hold each side. Gamma is the ingredient; GEX is the dish.

Where does gamma exposure data come from?

From open interest by strike and expiry, published daily by the exchanges through the OCC, combined with a pricing model to compute each contract's gamma. Different providers make different assumptions about which side dealers hold, so their GEX numbers differ. The shape is usually similar; the exact level is not.

What is zero gamma or the gamma flip?

The price at which the estimated dealer position changes sign. Above it dealers are net long gamma and their hedging dampens moves. Below it they are net short and their hedging amplifies moves. It is often close to the strike with the largest put open interest.

Does gamma exposure work on single stocks?

Yes, on names with liquid options, and it matters most around earnings and expiration. On thin names the estimate is noisy because a single large trade dominates the open interest. Index gamma is the most reliable because the book is deepest.

How is dealer gamma exposure calculated?

Take the open interest at every strike and expiry, compute each contract's gamma with a pricing model, then sign it by the side dealers are assumed to hold. Sum across the book and you get one number per name, usually quoted in dollars per one percent move.

Why do dealers hedge with shares rather than other options?

Shares are the cheapest and fastest way to offset delta, and the stock market is deeper than the options market in almost every name. Dealers do buy options from each other to manage the rest of their risk, and the visible daily flow is in shares.

When is a gamma reading most useful during the day?

At the open, when you decide how much room the day has. The map is built from the previous close, so it describes the structure you are trading into.

Do the exchanges publish gamma exposure directly?

No. They publish open interest and prices. Gamma exposure is a calculation on top of that, and every provider makes its own assumption about which side dealers hold.

What happens to gamma exposure on expiration day?

A large block of open interest disappears at the close, and with it the hedging attached to those strikes. The map for the following session can look different from the one that held all week. Monthly and quarterly expirations remove the most, which is why the days right after them feel unmoored.

Can I use gamma exposure for positions held for weeks?

For sizing, yes. A negative gamma regime argues for smaller positions and wider stops for as long as it lasts. For entry timing over weeks it is weak, because the map is rebuilt every night and the levels that matter today may be gone after the next expiration.

What is dealer gamma exposure, and why does it move the market?

By Daniel, The Philosopher Investor · updated September 18, 2026

Dealer gamma exposure is an estimate of how much stock market makers must buy or sell to stay hedged as the price moves. When dealers are long gamma they sell rallies and buy dips, which calms the market. When they are short gamma they do the opposite and amplify moves. The level where it flips is called zero gamma.

On the tape, 2026-09-22

At the 2026-09-22 close, SPY sat at 774.23 between a put wall at 750 and a call wall at 785, 69% of the way up that range, with dealers in negative gamma, which amplifies moves. Across 942 option books with a readable sign, 70% were in positive dealer gamma. Walls move as open interest rolls, so read this as yesterday's map.

Dealer gamma map for SPY, QQQ and IWM →

Why do market makers hedge at all?

A market maker sells you a call because that is their business, never because they think the stock will fall. To avoid carrying that risk they buy some stock against it. The amount they need changes as the price changes, and gamma is the rate of that change. High gamma means the hedge has to be adjusted often and in size.

Gamma exposure adds this up across every open option contract in a name or an index, weighted by open interest, to estimate the dealers' net position. It is an estimate because nobody publishes who is long and who is short. The standard assumption is that dealers are short the puts and calls that customers bought, and long what customers sold.

What happens when dealers are long gamma?

When the price rises, a long-gamma dealer's hedge is now too large, so they sell stock. When the price falls, it is too small, so they buy. That hedging flow pushes against every move. Days in positive gamma tend to be quiet, with dips bought and rallies faded, and the range compresses toward the strikes with the most open interest.

This is the regime most of the time in the major indices, because investors sell more calls than they buy and buy more puts than they sell, which leaves dealers net long gamma above the market. It is why index selloffs that start inside positive gamma often stall.

What happens when dealers are short gamma?

Below the zero gamma level the sign flips. Now a falling price forces dealers to sell stock, and a rising price forces them to buy. Their hedging pushes with the move instead of against it. Selloffs accelerate, rallies are sharp, and the daily range expands. Most of the violent days in any year happen in negative gamma.

The flip is a level, and it moves. As options expire and new ones are opened, the strike distribution shifts, and with it the point where the sign changes. A zero gamma level is yesterday's estimate, refreshed after each close.

How do you read a GEX chart?

A gamma chart shows a bar per strike, positive above the axis and negative below. The tallest positive bar above the current price is the call wall: the strike where the most hedging pushes against a rally. The tallest bar below is the put wall. The point where cumulative gamma crosses zero is the flip. Price tends to slow near the walls and speed up once it is through them.

Two things matter more than the exact numbers. Which side of zero the price sits on, because that sets the regime for the day. And how far it is from the nearest wall, because that is the room it has before hedging flow changes character.

How useful is it for a swing trader?

As context, very. Knowing that the index is in negative gamma tells you to expect wide ranges and to size smaller. Knowing that a call wall sits three percent above tells you where a rally will likely pause, which is a natural place to take some off. It is a map of where the mechanical flows sit.

As a standalone signal, less so. Gamma tells you how the market will move once it moves, never which way it will go. The direction still comes from the chart, the flow and the news. The map is for sizing and for targets.

Common questions

Is GEX the same as gamma?: Gamma is a property of one option: how fast its delta changes as the stock moves. GEX, gamma exposure, is the sum of gamma across all open contracts in a name, weighted by open interest and signed by who is assumed to hold each side. Gamma is the ingredient; GEX is the dish.
Where does gamma exposure data come from?: From open interest by strike and expiry, published daily by the exchanges through the OCC, combined with a pricing model to compute each contract's gamma. Different providers make different assumptions about which side dealers hold, so their GEX numbers differ. The shape is usually similar; the exact level is not.
What is zero gamma or the gamma flip?: The price at which the estimated dealer position changes sign. Above it dealers are net long gamma and their hedging dampens moves. Below it they are net short and their hedging amplifies moves. It is often close to the strike with the largest put open interest.
Does gamma exposure work on single stocks?: Yes, on names with liquid options, and it matters most around earnings and expiration. On thin names the estimate is noisy because a single large trade dominates the open interest. Index gamma is the most reliable because the book is deepest.
How is dealer gamma exposure calculated?: Take the open interest at every strike and expiry, compute each contract's gamma with a pricing model, then sign it by the side dealers are assumed to hold. Sum across the book and you get one number per name, usually quoted in dollars per one percent move.
Why do dealers hedge with shares rather than other options?: Shares are the cheapest and fastest way to offset delta, and the stock market is deeper than the options market in almost every name. Dealers do buy options from each other to manage the rest of their risk, and the visible daily flow is in shares.
When is a gamma reading most useful during the day?: At the open, when you decide how much room the day has. The map is built from the previous close, so it describes the structure you are trading into.
Do the exchanges publish gamma exposure directly?: No. They publish open interest and prices. Gamma exposure is a calculation on top of that, and every provider makes its own assumption about which side dealers hold.
What happens to gamma exposure on expiration day?: A large block of open interest disappears at the close, and with it the hedging attached to those strikes. The map for the following session can look different from the one that held all week. Monthly and quarterly expirations remove the most, which is why the days right after them feel unmoored.
Can I use gamma exposure for positions held for weeks?: For sizing, yes. A negative gamma regime argues for smaller positions and wider stops for as long as it lasts. For entry timing over weeks it is weak, because the map is rebuilt every night and the levels that matter today may be gone after the next expiration.

Primary sources

OCC, open interest and clearing data · www.theocc.com
Cboe, US options exchanges · www.cboe.com
SEC investor education on options · www.investor.gov

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Dealer gamma map for SPY, QQQ and IWM, free → Negative versus positive gamma, day by day → Call wall and put wall explained →

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