Gamma Exposure (GEX), explained with examples

Gamma describes how an option’s delta changes as its underlying price changes. A gamma exposure estimate aggregates those sensitivities over a specified set of positions or modeled positions. Before reading a chart, identify its units, contract coverage, snapshot date and position-sign assumptions.

Open interest counts outstanding contracts; it does not identify who holds the long or short side. A chart that assigns signs by option type is making a modeling choice. Its net value is not a direct observation of dealer inventory, future trades or the next market move.

In one commonly used scaling, a row’s dollar delta exposure per 1% underlying move is gamma × contracts × multiplier × spot² × 0.01 × assumed position sign. Check your provider’s definition before comparing numbers.

Our hypothetical row has gamma 0.02 per $1, 10 contracts, multiplier 100, spot $100 and an assumed positive sign. Its contribution is 0.02 × 10 × 100 × 100² × 0.01 = $2,000 of delta exposure per 1% move. That is a sensitivity estimate, not a $2,000 profit prediction. Changing the assumed position sign reverses this contribution.

Consider three supplied synthetic contributions: +2,000, −1,500 and +500, all in the same units. Net GEX is +1,000. Gross magnitude is 2,000 + 1,500 + 500 = 4,000, not the absolute net of 1,000.

If the last contribution is missing, the known net subtotal is +500. The complete net and gross totals are unknown. A missing observation is not an observed zero. Likewise, a filtered expiry slice is a subtotal rather than the complete chain. Try these distinctions in the example below.

Read the snapshot and assumptions first. Then compare the signed total, gross magnitude and location of contributions by strike and expiry. A positive net can coexist with a negative local region.

For a specified delta-neutral hedging model, a long-gamma position has a different local hedge response from a short-gamma position. Translating that relationship into market impact requires additional evidence about actual positions, hedge choices and liquidity. A prominent level is a research question to investigate, not a guaranteed entry or support line.

Before comparing two providers: match units, underlying, expiry coverage, source dates and sign conventions. If those differ, a disagreement in totals may be a disagreement in definition.