What is Gamma Exposure? A Trader's Guide to GEX

Gamma exposure measures how much options dealers — the market makers on the other side of nearly every options trade — must hedge in the underlying as price moves. It is the second derivative of an option price with respect to the underlying, multiplied across every contract a dealer is short or long, scaled into dollars per one-point move.

When the public buys calls, the dealer is short those calls and must continuously buy more of the underlying as price rises (and sell as it falls) to stay delta-neutral. That continuous, mechanical re-hedging is what GEX quantifies. It is not a speculative indicator — it is a measurement of forced flow.

The sign of net dealer gamma controls how the dealer must hedge:

• Positive gamma (dealers long gamma): dealers sell into rallies and buy into dips. This compresses realized volatility and creates "pinning" near heavy strikes. SPX expiration days with strong positive GEX historically grind sideways into the cash close.
• Negative gamma (dealers short gamma): dealers buy into rallies and sell into dips — they amplify moves in either direction. Realized volatility expands. The August 2024 yen-carry unwind, the 2018 Volmageddon move, and most multi-sigma SPX days share this regime.

The strike at which net dealer gamma flips from positive to negative is called the gamma flip (or zero-gamma level). Above it the dealer book is stabilizing; below it the dealer book is accelerating. Traders watch this line the way a chartist watches a 200-day moving average — it is one of the most reliable structural levels in index trading.

For each option contract, gamma is computed from the Black-Scholes formula using the live spot price, strike, time to expiry, implied volatility, and risk-free rate. That per-contract gamma is then multiplied by:

• The contract's open interest (the number of contracts outstanding)
• The contract multiplier (100 shares per contract for US equity options)
• The spot price squared, divided by 100, to express the result as dollars per 1% move
• A sign convention: call gamma is positive for dealers (they are typically short calls), put gamma is negative (dealers are typically long puts)

Summing this across every strike on the chain gives net dealer gamma exposure. Doing it strike-by-strike gives the GEX-by-strike profile that lets you find call walls and put walls. GEXRadar runs this calculation live across 3,500+ tickers every two seconds during market hours.

Three structural levels matter most:

• Call Wall: the strike with the largest positive call GEX. As price approaches it, dealer hedging accelerates and resistance builds. A clean break above the call wall usually requires a real demand catalyst — the wall doesn't move out of the way on its own.
• Put Wall: the strike with the largest negative put GEX. It acts as a magnet on the way down — dealers short puts must sell underlying into declines, which often bounces price off the level. Sustained breaks below put walls tend to coincide with volatility spikes.
• Gamma Flip (G-Flip): the price where cumulative dealer gamma crosses zero. Above it is the "stable" regime; below it is the "amplifying" regime.

GEX is not a forecasting tool. It does not tell you what direction the market will go. What it tells you is the shape of the path the market is likely to take if a move starts.

In a high positive-gamma regime, a trader can lean on intraday mean-reversion strategies with more confidence: short premium, fade extensions, expect rangebound action. In a negative-gamma regime, the same trader should respect trend, expect volatility expansion, and size positions for wider stops.

Knowing the regime before price tells you about it is the entire point of watching GEX. It is the map of where forced flow lives.

Gamma exposure is a powerful lens, but it is not a complete picture of dealer positioning. A few caveats:

• The sign convention (calls = dealer short, puts = dealer long) is a heuristic, not a fact. In practice dealers run mixed books.
• Open interest lags overnight; intraday GEX changes show up first in volume-weighted GEX, which GEXRadar exposes via the GEX-by-Volume toggle.
• Higher-order greeks — vanna and charm — drive flows that pure GEX misses. Days near OPEX and quarterly expiries often move more on charm than gamma.
• For very short-dated contracts (0DTE), the gamma calculation explodes near the strike; the chart can look extreme on expiration day for that reason alone.