0DTE and Dealer Gamma: Why Most GEX Numbers Miss It Entirely

If you trade the index intraday, most of the option activity around you now expires today. And there is an uncomfortable fact about that: the standard way of computing dealer gamma barely sees it.

This is not a criticism of any particular provider. It is a structural consequence of where the input data comes from, and it is worth understanding before you pay anyone for 0DTE levels — including me.

Where the gap comes from

Almost every published gamma-exposure number is built on open interest. Open interest is the count of contracts held at the end of the previous session. It is published once, after the close, by the exchange.

Now consider a 0DTE contract. It is opened and closed inside the same session. It expires today. It was never in yesterday's settled open interest, because yesterday it either did not exist or was a different expiry.

So a GEX figure computed from settled open interest is describing positioning that excludes most of what is being traded right now. The number is not wrong — it is accurately measuring something that is no longer the whole picture.

Why 0DTE gamma is disproportionately powerful

This matters more than the volume share alone suggests, because gamma is not distributed evenly across expiries.

Gamma — the rate at which an option's directional exposure changes as price moves — peaks sharply at the money as expiry approaches. A contract expiring in thirty days has its exposure spread over a wide range of prices. A contract expiring in four hours has enormous sensitivity within a few points of the strike and almost none outside it.

The practical consequence: a relatively small number of 0DTE contracts near spot can generate more hedging pressure than a much larger position in a distant expiry. And that pressure is concentrated in a narrow price band that moves as spot moves.

That is why intraday behaviour around certain strikes can feel violent and specific in a way that a monthly-expiry gamma profile does not explain.

What this means for anything sold as "0DTE levels"

Three questions worth asking any provider:

Does the number include today's expiry at all? If the calculation reads settled open interest, today's contracts are largely invisible to it. Ask directly.

How often is it recomputed? 0DTE gamma is spot-dependent and decays through the day. A level published at 08:30 and never revised is describing a surface that has materially changed by 11:00. This is true of all gamma, and dramatically more true of 0DTE.

What is assumed about who is short? The standard convention assumes dealers are net short customer flow. For monthly positioning that assumption has decades of behaviour behind it. For same-day flow — where a large share is short-dated speculation and hedging in both directions — it is a shakier assumption, and honest providers will say so rather than presenting the output as measurement.

The limits, stated plainly

I am not going to tell you there is a clean solution, because there isn't one.

Nobody outside a clearing firm observes dealer inventory. Intraday flow can be estimated from volume and trade-side inference, but inference is not observation, and anyone claiming certainty about same-day dealer positioning is overselling. What is achievable is a surface that re-measures as the session runs rather than one fixed before the open, and honesty about which parts are computed and which are assumed.

That is a real improvement over a static morning number. It is not omniscience, and a service that implies otherwise is telling you something it cannot know.

How to use short-dated gamma without fooling yourself

Treat concentration as a location, not a prediction. A strike carrying heavy short-dated gamma is a place where the market's own hedging is likeliest to react. It says nothing about direction.

Expect it to move. Unlike a monthly wall, a 0DTE concentration can migrate through the session as positions open and close. If your read was formed at the open and you are trading it at noon, you are trading a stale map.

Watch what happens at the level, not what should happen. The value is in the reaction. If price reaches a heavy strike and absorbs, that is information. If it slices through, that is also information — and it happens more often than the marketing suggests.

Remember the clock. Whatever pressure exists decays to nothing at expiry. A 0DTE level at 15:45 is a different object from the same level at 10:00.

What I do about it

Sharpnel draws dealer-gamma levels on the same chart as the order flow, and the surface re-measures through the session rather than being fixed before the open. Every trading morning at 08:30 ET the ES and NQ levels are published, and at 16:15 ET each is marked against that session's real high and low — misses kept.

As of 31 July 2026 that record runs to 88 graded wall tests, of which 28 broke. Roughly a third. I publish that because it is the honest frame for everything above: these levels tell you where the market is likeliest to react, not where it must stop. The live figure is on the record page, and if it has moved since this was written, that page is right and this sentence is stale.

The summary

Short-dated options changed where intraday hedging pressure sits, and the standard open-interest calculation was not designed for them. Before paying for anything sold as 0DTE dealer positioning, ask whether today's expiry is in the number at all, how often it updates, and what the provider will admit to assuming. The answers vary far more than the marketing does.