Dealer Gamma Explained

Dealer gamma is the net gamma held by the firms that sell options, and it tells you how their hedging will react when price moves. When dealers are long gamma, their hedging leans against moves. When they are short gamma, it goes with them. That hedging happens in ES and NQ futures, so it matters even if you never trade an option.

This guide covers the mechanics, the levels built on them, and the assumptions that make those levels less certain than they look. Examples use round numbers, with ES near 6000.

Why dealers trade futures at all

Every option has a seller, usually a dealer. A dealer wants to earn the difference between the bid and the ask, not to bet on direction. Selling an option creates price risk, so the dealer removes that risk with an offsetting trade in the underlying market.

S&P 500 options are hedged mostly in ES, and Nasdaq-100 options mostly in NQ. Those orders do not reflect an opinion. They follow from arithmetic, which is what makes them worth mapping.

Delta, gamma and the hedge that never stays right

Delta is how much an option's value moves for a one-point move in the market. For a dealer, it is the hedge ratio. A dealer who has sold 1,000 SPX calls with a delta of 0.50 buys about 1,000 ES contracts to be flat.

Gamma is how fast delta changes. If delta is speed, gamma is acceleration. Because delta shifts as price moves, yesterday's hedge is never quite right today, and often not a few minutes later.

Gamma is highest close to the strike and close to expiry. That is why 0DTE options, which expire the same day, carry so much weight:

• One week to expiry: a 10-point move forces about 70 ES contracts of re-hedging per 1,000 at-the-money options.
• A few hours to expiry: the same move forces about 210 contracts.

Long gamma and short gamma

A dealer who owns options is long gamma. A dealer who has sold them is short gamma. The two re-hedge in opposite directions.

• Long gamma: price rises, so the dealer sells futures. Price falls, so the dealer buys. Moves tend to be absorbed, and ranges tighten.
• Short gamma: price rises, so the dealer buys futures. Price falls, so the dealer sells. Moves tend to extend, and ranges widen.

A worked example

Index investors buy a lot of put protection, which leaves dealers short those puts. Say a dealer is short 1,000 SPX puts with a delta of −0.30. The hedge is about 600 ES contracts short.

The market falls and the delta grows to −0.40. The hedge must now be 800 contracts, so the dealer sells 200 more into the fall. When the market recovers, the dealer buys them back. That is short gamma: hedging that adds to the move.

What GEX measures

Gamma exposure (GEX) turns all of this into one number per strike: the dollar amount of futures dealers would trade for every 1% move.

A strike showing +$5bn means roughly $5 billion of dampening hedging per 1% move is concentrated there. By convention, calls count as positive and puts as negative. That convention assumes customers mostly buy puts and sell calls, which leaves dealers long the calls and short the puts. It is an assumption, and we come back to it below.

The gamma flip: the regime line

The gamma flip, also called zero gamma, is the price where total dealer gamma crosses from positive to negative. You cannot read it off one strike. Total gamma depends on where price is, so a model recalculates the whole option chain at many hypothetical prices and finds the crossing.

The useful question is not "will price bounce here?" It is "which side am I on, and how far?"

• Well above the flip: usually the calmer regime, with more back-and-forth.
• Well below the flip: usually the faster regime, where fading moves is more dangerous.
• At the flip: a transition zone. A small move can change the character of the session.

The flip also moves through the day as time passes, volatility changes and new positions arrive. In our own session grading, it has worked better as a regime marker than as a level that holds on the first touch.

Call walls and put walls

The call wall

The call wall is the zone with the most positive dealer gamma. As price rallies into it, dealers who are long those calls sell more and more futures. That steady supply is why it often behaves like resistance. Near expiry, the same mechanism can make it act as a magnet.

The put wall

The put wall is the zone with the most negative dealer gamma, usually below price. It often reacts on the first test, but dealer hedging is not the reason. Holders of protection take profits there, and when dealers buy those puts back, they also buy back their futures hedge.

Around and below that level, dealers are short gamma and sell as price falls. Once the profit-taking is done, a clean break can turn into a fast move lower. That makes a put wall a level to watch, not a level to buy blindly.

One big strike is not a wall

A huge position at a single strike may be one fund's structure. A wall backed by gamma on the neighbouring strikes is more likely to reflect broad positioning, so look for clusters rather than the tallest single bar.

What gamma levels cannot tell you

Every gamma tool rests on the same limits. Knowing them is what separates using a map from believing in one.

• Who holds what: dealer positioning is estimated, not observed. If customers are buying calls at a strike, the true sign of gamma there can be the reverse of what the model shows.
• Today's new positions: open interest is counted once a day, so anything opened today is missing until tomorrow. This is the main reason 0DTE is hard to model.
• What happens next: levels show hedging pressure, not a forecast. News, large orders and sentiment can overpower them.

The symptom of a wrong assumption is visible on the chart: a wall that price keeps slicing through, or a rally that speeds up into a call wall instead of stalling. When you see that, trust the level less.

Common questions