Gamma exposure (GEX) for S&P 500 and Nasdaq-100 stocks

What is gamma exposure (GEX)?

Gamma exposure (GEX) estimates how much options hedging could change when a stock moves. It adds up each contract's gamma, weighted by open interest and the stock price, and is usually quoted per 1% move. Positive totals are linked to dampened moves and negative totals to amplified moves, but only under the model's assumptions.

Gamma describes how fast an option's delta changes as the stock price moves. A market maker hedging delta may need to re-hedge as that price changes. A concentration of gamma at one strike could therefore mean substantial buying or selling under those assumptions. GEX attempts to size that effect, not predict the next move.

Is GEX the same as actual dealer positioning?

No. Public data shows how many contracts are open, not who holds them. PredixLab's gamma exposure is estimated from public open interest and model assumptions: calls are counted as positive gamma and puts as negative, a common convention. Actual dealer positions are unknown, so treat GEX as a model, not a fact about anyone's book.

The convention broadly assumes customers buy puts and sell calls to dealers. Covered calls, spreads and institutions on both sides can break that picture. The sign belongs to the model, not an observed holder. Read how PredixLab builds its options data before interpreting the totals.

How do you read a gamma exposure chart?

The bars by strike show where modeled gamma is concentrated. Above zero means call-driven, positive exposure; below zero means put-driven, negative exposure. Start with the largest bars near the current price: gamma is generally highest near the money and close to expiry. Then compare the positive and negative contributions, rather than reading either alone.

Illustrative example, not market data. Stock A trades at $100. The 105 call has 20,000 contracts open, with gamma 0.04. Per contract: 0.04 × 100 × $100² × 1% = $400, and × 20,000 = +$8.0M per 1% move.

The 95 put has 15,000 open, with gamma 0.035: $350 per contract, giving −$5.25M. In this two-strike toy, net GEX is +$2.75M per 1% move, the regime reads Positive, the call wall is 105 and the put wall is 95.

Use the near-spot view to focus on nearby concentrations, then all strikes to see the wider distribution. The illustration is deliberately limited to two strikes; it is not a complete options chain.

What do positive and negative gamma mean?

Under the model, positive net GEX means hedgers would trade against the move (sell into rallies, buy dips), which is associated with calmer price action. Negative net GEX means they would trade with the move, which is associated with larger swings. These are tendencies under assumptions, not predictions, and many other forces move prices.

The Gamma Map labels these regimes “More stabilizing under the model” and “More volatility-amplifying under the model.” Zero net GEX is Neutral: balanced modeled exposure. In the Stock A example, if heavy put buying pushed net GEX below zero, the regime would read Negative. That would still not establish anyone's actual hedge.

What are the gamma flip, call wall and put wall?

The gamma flip is the modeled price where net GEX would cross zero, shown with its distance from the current price. The call wall is the strike with the largest modeled call gamma; the put wall has the most negative modeled put gamma. These are concentrations of open interest, not support or resistance guarantees.

Stock A's walls are 105 and 95 in the illustration. A wall shift means the largest concentration moved to a different strike from the previous session; compare previous and current values. Neither wall promises that price will stop there.

Why did gamma exposure change from the previous session?

The Gamma Map splits the change from the previous session into four parts: open interest changes, price and Greeks changes (the stock moved or time passed), new contracts and removed contracts. It then lists the contracts that drove most of the change, so you can inspect the contributions behind the headline number.

Top drivers show ΔOI, ΔGEX and share of change. A contract can also carry an unusual options activity flag. Continuing the illustrative Stock A example, open interest on the 105 call rose 4,000, explaining most of a GEX increase. This describes a modeled contribution, not trader intent.

Which expirations are included?

The Gamma Map has three windows: all expirations, expiring within 7 days, and expiring within 30 days. Short-dated options carry more gamma near the money, so the 7-day view can look very different from the full view. Compare windows before treating a concentration as representative of the whole chain.

Keep the data date and expiry window consistent when comparing sessions. A change in the selected window can change the total without implying new positions. For a separate, dated volatility-change workflow, see the IV crush guide.

Which stocks, and which date will you see? (Free vs Premium)

The Gamma Map covers S&P 500 and Nasdaq-100 stocks. It updates once per trading day. Free shows gamma exposure with a 10-calendar-day delay; Premium ($20/month or $192/year) shows the latest published trading day. The model and full Gamma Map features are the same on both plans; only the data date differs.

The options job runs once per trading day, around 7:30 am ET (6:30 am ET in winter) the morning after the session, and can take up to an hour. Always check the data date shown on the map. The delay counts calendar days, not trading sessions.

What can't gamma exposure tell you?

Gamma exposure cannot tell you who actually holds the options, whether those positions are hedged, which direction the stock will move or how far it will go. The map uses daily public open interest, not changes within the session. A large modeled concentration is context for independent analysis, not a trading signal or investment advice.

Public open interest and model inputs can be delayed, missing or wrong. Some symbols or dates may have no map. Review the known limitations and check the data date before comparing figures.