Gamma Exposure: How Dealer Gamma Moves the Market Price

Before this article: Gamma Hedging: Why Dealers Adjust Their Coverage All Day Long.

From one dealer to the whole market

The previous articles described a single dealer hedging one position. In reality, there isn't just one dealer: there are thousands of positions spread across dozens of firms, in hundreds of different strikes, all hedging with the same mechanical logic at the same time.

Gamma Exposure (GEX) is how all of that gets summed into a single number: how much hedging need exists, in aggregate, across the options market for an asset.

The aggregate formula

The same formula from the previous article, replacing "one specific contract" ($N$) with the total open interest at that strike ($OI$, Open Interest, how many contracts remain open in the market):

$$ \Delta Q_{\text{market}} = \Gamma \times \Delta S \times OI \times M $$

Where:

$\Delta Q_{\text{market}}$ = total quantity of the underlying that dealers, in aggregate, need to adjust.
$\Gamma$ = Gamma of the options at that strike.
$\Delta S$ = the price move.
$OI$ = open interest (total open contracts) at that strike.
$M$ = the contract multiplier.

Key idea: it doesn't matter how many different firms are on the other side of each contract. If they all hedge with the same mechanical logic (Delta Hedging + Gamma Hedging), the aggregate effect is predictable in magnitude, even without knowing exactly which firm executes each order.

flowchart LR
    A[Strike 1: Gamma × OI] --> D[Aggregate sum]
    B[Strike 2: Gamma × OI] --> D
    C[Strike N: Gamma × OI] --> D
    D --> E[Total market<br/>Gamma Exposure]
    E --> F[Aggregate hedging<br/>pressure on price]

Numeric example

Example: at a strike on the underlying with 0.02 Gamma and 50,000 contracts of open interest (OI), if price moves 20 points:

$$\Delta Q_{\text{market}} = 0.02 \times 20 \times 50{,}000 \times 100 = 2{,}000{,}000 \text{ index units}$$

That's the magnitude of adjustment dealers, in aggregate, need to execute at that strike alone. Multiply that across dozens of active strikes on a given day, and it's clear why aggregate hedging is a real force on price, not a minor detail. Illustrative figures.

Why this isn't uniform across strikes

Not every strike contributes equally. Strikes with heavy open interest and high Gamma (near the current price) dominate the total; far strikes barely add anything. Later in this guide, this translates into concrete levels you can see on the map: the Flip (Gamma Flip), the point where total market Gamma Exposure flips sign, and the Call Wall/Put Wall levels, which are the strikes where that concentration is strongest.

Note: exactly how call and put contributions combine into the final number (Net GEX) is covered in a dedicated article later in this guide: here we're just establishing that the aggregation exists and why it matters.

Next step

You now know that aggregate Gamma Exposure can be, on net, positive or negative. That distinction defines two completely different market regimes.

Continue with: Long Gamma vs Short Gamma Regime: Why the Market Trends or Mean-Reverts