SPX GEX Today: Gamma Exposure by Strike

What is Gamma Exposure (GEX)?

Gamma exposure (GEX for short) measures how much dealers must buy or sell of the underlying index (here, SPX) as prices move, in order to stay hedged on the options positions they hold. Because market makers are the counter-party to most options trades, their aggregate hedging flow can be a large buyer or seller of the underlying.

Positive GEX means dealers are net long gamma. As price rises they must sell into the move, and as price falls they must buy, a stabilizing, volatility-suppressing regime. Negative GEX inverts that flow: dealers chase price higher on the way up and add to the sell pressure on the way down, so intraday moves get amplified and trends persist.

How dealers hedge, and why traders watch it

Every figure on this page rests on one convention about who holds which side. Against customer flow the dealer is long the calls and short the puts: covered calls and collars sell calls to the desk, and demand for downside protection sells puts to it. Long calls carry positive gamma. Short puts carry negative gamma. The sign on net GEX is simply which of those two sides is larger on the day.

When the long-call side dominates, the book is long gamma. Its delta rises as price rises, so the desk sells the index into strength, and its delta falls as price falls, so it buys the dip. That two-sided hedging is what pulls price toward the strikes carrying the heaviest gamma. When the short-put side dominates, the book is short gamma and the arithmetic runs the other way: a short put carries positive delta that grows as spot falls, so a delta-neutral desk sells into the decline, and sells more the further it goes. That is amplification rather than support, which is why heavy put gamma below spot is not the floor it is usually described as. The gamma squeeze story runs on the opposite positioning, a desk short the calls, which this convention does not grant. None of it is measured: open interest records that a contract exists and never which side a dealer holds.

The reason traders watch the GEX chart is the flip level between positive and negative gamma. Under the dealer convention above, hedging runs against the move above the flip and with it below. That is the flow the convention implies, not a measurement of how often price has behaved that way, and this page publishes no hit rate for it.

Gamma describes what a hedger has to do when price moves. Vanna exposure and charm exposure describe what the same book does when price does not move, and the SPX figures for both, from the delayed option chain, sit in the vanna and charm exposure section further down this page. Why the market moves in the last hour separates that flow from the closing auction, which is a different thing that lands in the same window.

How to read this chart

The top metrics tell you the four levels most GEX-informed traders track:

• Zero Gamma / Flip: the price where net dealer gamma crosses zero. Above = suppression. Below = amplification.
• Call Wall: the strike above spot with the largest positive call gamma, where dealer hedging is most concentrated above spot.
• Put Wall: the strike below spot with the largest negative put gamma, where dealer hedging is most concentrated below spot. Call wall and put wall compared covers why the put wall does not simply mirror the call wall.
• Swing Line: the lowest positive-gamma strike between the walls. Below it, hedging flow amplifies moves. Above it, hedging suppresses.

Underneath, the chart shows whichever the current data supports. When the daily snapshot is driving the page you get the key gamma levels, the levels above and below spot strikes it publishes, ranked by distance from spot. When the page is computing from the delayed option chain instead, you get net GEX by strike: green bars are net positive gamma (dealers pin toward the strike), red is net negative (dealers reject it), and big clusters of one color near spot are where that hedging would concentrate if the convention holds. Below the widget, the dealer gamma by strike chart draws the strikes nearest spot from the delayed option chain on either path, in the same colors. It is the gamma heatmap's book, so its bars do not add up to the net GEX figure.

How this chart is calculated

The walls come from a full-chain snapshot built once each morning before the open: settled open interest for every listed SPX strike and expiry, roughly 21,000 contracts, crossed with per-contract implied volatility. For each contract we take gamma × open interest × 100 × spot, sign calls positive and puts negative (dealer perspective), and aggregate to a net figure per strike. That is the standard public formulation, no proprietary smoothing, no vendor-locked feed.

Because the input is settled open interest, the walls are fixed for the session, they do not move tick by tick. What does update is everything around them: a refresh every 30 minutes through the cash session repoints spot and the expected range. Alongside the walls we publish the net change in contracts open across the chain from the previous settlement to this one, counted from our own archive. If that snapshot is missing or too old to describe today's tape, the page falls back to computing the same formula from the delayed option chain, fewer expirations, no open-interest comparison, but the arithmetic is identical.

The front-expiry row above covers the contracts expiring on the nearest listed date and nothing else. Its flip and walls are withdrawn, and the row says why; what the extra night changes covers why a same-day round trip never reaches the settled open interest any of these levels are built from. For the probability the option chain prices on settling above a specific level, rather than the range, the market-implied odds page reads it off the same chain.

Learn more

• What is Gamma Exposure (GEX)? A Complete Guide, Understanding gamma exposure: how it is calculated, and how modelled dealer hedging is read as damping or amplifying moves.
• GEX Flip Price Explained: The Volatility Regime Line, The GEX flip price marks where dealer gamma transitions from positive to negative, and what crossing it does and does not imply.
• Call Wall and Put Wall: What They Are and When They Hold, Call wall vs put wall: how each is picked from gamma-weighted open interest, why the put wall is not a mirror image, plus free dated SPX levels.
• 0DTE Gamma Exposure: What the Front Expiration Measures, What 0DTE gamma exposure is, what the front expiration's open interest, strike count and net gamma measure, and why walls ranked from it fail late in the session.
• Swing Line Explained: The Volatility Threshold vs the GEX Flip, What the Swing Line in dealer gamma models measures, how it differs from the gamma flip, and what it does not tell you.