Gamma

Gamma measures how much an option's delta changes for a one-point move in the underlying - the rate of change of delta, or delta's own sensitivity to price. Gamma is largest for at-the-money options nearing expiration, and it is the mechanism that forces dealers to continuously re-hedge, the basis of gamma exposure (GEX).

If delta is an option's speed relative to the underlying, gamma is its acceleration. A high-gamma option's delta changes quickly as price moves, which means a dealer's hedge on that option goes stale fast and must be adjusted often. A low-gamma option's delta barely moves, so its hedge stays roughly correct for longer.

Gamma is not evenly distributed across the chain. It peaks for at-the-money strikes and grows sharply as expiration nears, because a small move in either direction can flip a near-the-money, near-expiry option between likely worthless and likely in the money. That is why 0DTE gamma is described as concentrated: a large share of a session's total gamma often sits at the handful of strikes closest to the current price.

This concentration is the direct link to dealer hedging. Every re-hedge a dealer makes to stay delta-neutral is driven by gamma - it is the reason the hedge must move at all as price changes. Summed across the chain and signed by which side of the book dealers are estimated to hold, that hedging obligation becomes gamma exposure (GEX), and its sign determines whether the resulting flow dampens or amplifies the move.

Gamma also carries convexity risk for option sellers. A short-gamma position loses money at an accelerating rate as the underlying moves away from the strike, which is why short-premium strategies can look stable for long stretches and then lose sharply in a single fast session - the same convexity that makes gamma valuable to option buyers makes it dangerous to sellers who are not hedging it.

Mathematically, gamma is the second derivative of an option's price with respect to the underlying - the same relationship acceleration has to velocity, applied to price rather than motion. This convexity is what makes owning options structurally different from owning the underlying directly: a long option position can gain in value from movement itself, in either direction, because gamma means its delta improves as the underlying moves further from the strike.

Individual contract gamma is small, but a dealer's book is not one contract - it is thousands of open positions across every strike and expiration on the chain. Summed and signed by which side dealers are estimated to hold, that aggregate becomes gamma exposure (GEX), and the specific netted, combined figure quoted as a single headline number is what net gamma exposure describes. The rate at which even that aggregate gamma itself is changing, as price and time move, is captured by the third-order Greeks speed and color.

Gamma also underlies a widely discussed concept called gamma scalping: because a long-gamma position's delta improves automatically as the underlying moves, some market participants re-hedge that changing delta by trading the underlying, in effect systematically buying dips and selling rallies. Whether that activity is profitable in aggregate depends on whether the resulting trading gains outweigh the time decay (theta) paid to hold the position - the trade-off that defines the relationship between gamma and theta across the options market generally.