How to read a GEX heatmap: strikes, expiries, and walls

A GEX heatmap groups estimated options exposure by strike and expiration. Its colors can make a complicated chain easier to scan, but a bright cell is not an instruction to buy or sell. The first job is to identify what the map measures and which positions it assumes.

A GEX heatmap is a chart of estimated gamma exposure across an option chain: strikes on one axis, expiration dates on the other, and color intensity showing how large the estimated exposure is at each point. The value in each cell is not a measurement of dealer inventory. It is an estimate built from public data plus assumptions, and reading it well starts with knowing what those assumptions are.

What the grid shows

Gamma measures how fast an option's delta changes when the underlying moves. Per-option gamma is often largest near the money and close to expiration (Options Industry Council, Gamma). Total exposure also depends on how many contracts are open. A farther strike or later expiration can dominate a heatmap if its position count is much larger.

Each cell combines option gamma, a position count, a contract multiplier, and an assumed position sign. Units vary: some maps show hedge shares for a $1 underlying move, while others show hedge dollars for a 1% move. Those are different quantities. For the latter convention, a common local approximation is signed gamma × open interest × multiplier × spot² × 0.01. Check the legend before comparing totals. SqueezeMetrics' published GEX research explains dealer delta sensitivity and why inferred ownership matters to the hedge direction.

Long calls and long puts both have positive gamma; short calls and short puts have negative gamma (OIC, Gamma). A heatmap that assigns positive call-side exposure and negative put-side exposure is therefore encoding a position-sign model, not an intrinsic difference between call gamma and put gamma. Public open interest cannot establish which side dealers hold. Negative put-side GEX is a modeled ownership convention; a purchased put still has positive gamma.

A hypothetical example

Suppose a hypothetical index trades at 5,000 with an expiration at the end of the week. Open interest is concentrated at the 4,950, 5,000, and 5,050 strikes. If the gamma and position counts make those the largest exposures, their cells will stand out. A large open-interest position on a later expiry could still outweigh a smaller front-expiry position. These are invented inputs, not an observed market map.

Hold the hypothetical contracts fixed and change the ownership assumption. If dealers are short the calls at 5,000, an upward move can increase the amount of stock needed for a delta hedge. If dealers are long those calls, the hedge adjustment runs the other way. The raw open interest is unchanged, but a properly signed exposure estimate must change when the ownership assumption changes.

Read the sign together with the ownership convention. Color alone cannot establish a hedge direction.

A practical reading checklist

1. Learn the conventions before the colors: which axis holds strikes, which holds expirations, what the scale measures, and whether the estimate uses open interest alone or adds volume.
2. Find the current price and the nearest expiration. The cells that matter for near-term flow sit near the money on the front rows, where gamma is largest.
3. Read the sign on each side of price. A spot price inside a large positive region and one inside a large negative region describe different hedging behavior under the model.
4. Look at clusters rather than single cells. A gamma wall is a concentration, and its width and distance from price matter more than its peak (What a wall is).
5. Check the ingredients. Ask how fresh the open interest is and whether expiring contracts have already dropped out, because stale inputs produce bright cells that no longer exist (Open interest vs. volume).
6. Re-read the map after the close and after expirations roll. Open interest updates once a day, and expiring rows disappear.

Where the estimate ends

The most common misuse of these charts comes from skipping their limits:

• It is an estimate. Public open interest counts contracts, not holders. It cannot say who is long, who is short, or whether positions belong to dealers at all. Direction has to be inferred, and inference is where error enters.
• The sign is a model. Negative colors on the put side reflect a dealer-ownership assumption, covered above, not option math.
• Hedging is conditional. The map shows where re-hedging pressure would exist if positions are as modeled and if dealers hedge in the underlying. Real desks hedge by their own rules, at their own times, to their own degrees.
• No level is guaranteed. Pinning and compression stories describe tendencies, not mechanical certainties. A wall that holds twice can fail on the third test without any rule being broken. The regime view in Reading the gamma flip is built for exactly that uncertainty.
• It is not a forecast. The map locates sensitivity. Price discovery happens for reasons the map does not contain.

The honest use of a GEX heatmap is as a map of where options-driven hedging sensitivity concentrates under stated assumptions, paired with the question of what would invalidate the read. It identifies places worth watching. Price behavior and other evidence still have to support the interpretation.

Sources and further reading

• Options Industry Council, Gamma
• Options Industry Council, May Office Hours FAQs
• SqueezeMetrics, The Implied Order Book

Educational content only. This is not personalized investment advice and not a recommendation to buy or sell any security. Options involve risk and are not suitable for every investor.

Prepared with AI assistance; reference links were checked before publication.