What is gamma exposure (GEX)?

Start with who is on the other side

Every option you buy, somebody sold you. That somebody is usually a market maker, and they are not taking the other side of your opinion. They run a book and hedge it in the underlying so their profit comes from the spread rather than from direction.

When you buy a call, the dealer who sold it buys shares to offset the risk. If price rises, that hedge no longer covers them and they must buy more. If price falls, they have hedged too much and must sell some back. That constant re-adjustment is not optional — it is the cost of staying neutral.

Gamma is the rate the hedge changes

Delta tells you how much stock a dealer needs to hold right now. Gamma tells you how fast that number changes as price moves. High gamma means the hedge has to be rebalanced aggressively for small moves; low gamma means it barely moves at all.

Gamma exposure — GEX — aggregates that across every strike and expiry on the board, weighted by open interest. The result is an estimate, strike by strike, of how much hedging pressure sits at each price.

The sign matters far more than the size

When dealers are net long gamma, they hedge against the move: selling into rallies, buying into dips. That absorbs energy. Ranges tighten and moves stall — most of all when heavy positive size sits right at price, which narrows the range from both sides rather than acting as support.

When dealers are net short gamma, they hedge with the move: buying as it rises, selling as it falls. That adds energy. Measured on 906 sessions, negative gamma has run about a quarter more movement over the following days than positive gamma, in both halves of the sample.

This is why a single number labelled 'net GEX' tells you less than its sign does. A billion dollars of positive gamma and a billion of negative describe opposite days — but how far above zero you sit added nothing when we tested it.

What GEX does not tell you

A still board does not tell you direction. Dealer positioning describes how the market will behave if it moves, not which way it will go. The only directional reads we have found come from change — size being added or removed during the session — never from where the size already sits.

It also does not tell you which levels matter today. A strike carrying enormous gamma four percent away is not in play on a quiet session — we measured this across 742,863 dealer walls and the pattern is stark. Distance dominates. That is why FlowMonkey prices every level by whether your ticker can actually reach it, rather than drawing them all at the same weight.