Guide · July 25, 2026

Gamma exposure by strike: how a GEX chart is built and what it assumes

Written and reviewed by ConvexValue · Updated July 25, 2026

A gamma exposure chart takes the option chain, computes how much gamma sits at each strike, signs it according to an assumption about who is on which side, and plots the result. The largest bars get called the call wall and the put wall, and traders watch them as potential support and resistance.

It is a genuinely useful map. It also rests on one assumption that is worth understanding before you trade off it.

How the number is built

For each contract, gamma from the snapshot is multiplied by open interest and by a contract multiplier, giving the gamma held in that contract. Summed by strike, that produces a gamma profile across the chain.

The signing step is where the convention enters. The standard approach assumes market makers are short calls and short puts — the other side of retail and institutional buying — and signs the result so that:

  • above spot, dealer gamma is typically positive, implying they sell into strength and buy into weakness;
  • below spot, dealer gamma is typically negative, implying they sell into weakness.

That mechanism is the whole basis of the claim that these levels can slow price down or accelerate it. Positive-gamma hedging dampens moves; negative-gamma hedging amplifies them.

The assumption nobody can verify

Open interest is published. Who holds it is not. No exchange publishes whether market makers are net long or net short the gamma at a given strike, so every GEX chart substitutes a convention for that missing information.

Most of the time the convention is reasonable — dealers really do provide liquidity to net buyers of options. But it is an assumption, and it fails precisely in the situations people most want the chart for: a large institutional seller of calls flips the sign at that strike, and the chart cannot know.

Treat a GEX profile as a map of where hedging flows would be concentrated if the usual positioning holds, not as observed positioning.

Daily open interest and intraday levels

Open interest updates once a day, after the close. That has a specific consequence for anyone reading these levels intraday: the position side of the calculation is fixed for the whole session.

Levels still move during the day, because gamma itself depends on spot and implied volatility, and both move. But they move as a re-pricing of this morning’s positions, not as a response to today’s trading. A wall that formed from heavy trading this afternoon will not appear until tomorrow.

This is the single most common misreading of an intraday gamma chart.

Choosing an expiration window

Gamma concentrates in near-dated contracts, so the expiration window changes the picture more than any other setting:

  • Front week only — the right lens for a short-horizon question. Longer-dated open interest, which will not be hedged for months, is excluded.
  • All expirations — the right lens for structural levels, and the wrong one for this week, because it buries near-dated strikes under open interest that is not currently driving anything.

A chart that does not state its window is not readable.

What the levels do and do not mean

Concentration marks where contracts were written. Sometimes that is a level that matters because contracts were written there; often it is a round number people chose because it already mattered. The causal arrow is not recoverable from the chart, so the honest use is as a list of prices where something might happen — alongside everything else you look at, not instead of it.

Fields you need

gamma, open_interest, day_volume, strike_price, expiration_date, contract_type and underlying_price, all from the options snapshot on the free data tier.

Watch it built

More in the gamma exposure and key levels section of the demo library, and see open interest by strike for the unsigned version of the same data.

This is research and education, not investment advice.