What the 0DTE share of volume actually means

What the 0DTE share number actually counts

A 0DTE share is a ratio of contract volume, and the numerator and denominator both need naming before the number means anything. Cboe's published figures are usually specific to SPX index options; a share quoted for one index is not the share for the whole US listed options market, and a share for one session is not an average daily figure.

Read the definition attached to any 0DTE percentage before comparing it with another. Most disagreements about how large the 0DTE market is turn out to be disagreements about which denominator was used.

• Numerator: contracts traded during the period whose expiration is that same trading day.
• Denominator: usually one product family such as SPX index options, sometimes a broader index or ETF group.
• Period: a single session, a monthly average or a quarterly average daily volume figure.
• Excluded by construction: any name without a same-day expiration listed, which is most single-stock options.
• Not counted at all: open interest, premium committed or the direction of the activity.

What actually drove the growth in the share

The share grew mainly because the supply of same-day contracts grew. Cboe's own research traces SPX 0DTE from roughly 5% of SPX options volume in 2016 to about 50% by August 2023, and links the step change to the completion of an every-weekday SPX expiration calendar after Tuesday and Thursday expirations were introduced. Once a same-day contract exists on all five weekdays, activity that previously waited for Friday can happen any day, and it shows up in the ratio immediately.

Cboe's later research note records the scale that followed: SPX 0DTE trading grew more than five-fold over three years to average almost 2 million contracts a day, with retail estimated at 50-60% of SPX 0DTE volume. Those are participation and volume facts. None of them is a statement about market direction.

Why a rising share is not a sentiment reading

A sentiment measure needs to distinguish what participants want from what they are able to do. The 0DTE share does not. A rise can come entirely from a calendar change, from a migration of existing activity into shorter expiries, or from spread structures that print several contracts per position, and none of those tells you whether anyone is bullish.

Cboe's research also found the flow itself to be closely balanced. On one heavily traded SPX put in August 2023, over 100,000 contracts traded while market makers ended up short about 3,000, with roughly 52,000 bought against 55,000 sold. A number that large resolving into a position that small is the clearest demonstration available that volume and net positioning are different quantities.

• The share rises when supply of same-day contracts rises, independent of any opinion.
• Buying and selling both add to the numerator, so a two-sided market inflates it symmetrically.
• Multi-leg defined-risk structures multiply contract counts without multiplying positions.
• Cboe reported over 95% of 0DTE trades done in a limited-risk format, either long outright or short via spreads, with a maximum loss known at entry.
• None of the above carries information about the direction of the underlying.

What Cboe's own research says about market impact

The most common secondary claim about 0DTE is that it destabilises the intraday market through dealer hedging. Cboe has published directly on this and reached the opposite conclusion, which is worth reading in full rather than through summaries. The figures below are from Cboe's own volatility-insights work and its later positioning note, and readers should check the current versions since these measures are updated over time.

This does not make short-dated gamma irrelevant to research. It means the mechanism is smaller and more balanced than the popular version of it, and that any claim built on aggregate 0DTE volume alone is starting from the wrong quantity.

What the share does and does not do to intraday gamma

Gamma exposure is a model output, not an observation. It combines option gamma with contract size, spot and an assumption about who is long and who is short, usually applied to open interest. Because public data does not disclose the dealer-versus-customer split, two providers can compute different exposure values from the same chain, and both can be internally consistent.

At same-day expiries the model is most volatile precisely because the underlying quantity is: near-the-money gamma is largest close to expiration, so the map redraws as spot moves through the session. That makes 0DTE exposure a useful description of where sensitivity is concentrated right now. It does not make any strike a magnet, a wall or a level the market must respect.

• Gamma exposure requires a positioning assumption that public data cannot confirm.
• Short-dated exposure changes fastest, so a level read at 10:00 may be irrelevant by 14:00.
• Volume adds to the picture only after it settles into open interest overnight.
• Treat gamma wall, flip and magnet language as hypotheses about mechanics, not as rules.

How to use the number in a research routine

The share of volume is context, and it belongs at the start of a session read rather than inside a conclusion. Knowing that a large share of today's activity expires today tells you which expiries deserve attention and how quickly the picture will change. It tells you nothing about which way anything is going.

Realtime Options shows 0DTE activity and modelled gamma exposure by strike alongside the rest of the chain. It does not issue signals or alerts framed as recommendations, it does not build option strategies or payoff diagrams, and it cannot tell you whether short-dated activity is speculation, hedging or yield harvesting.

• Use the share to decide which expiries to look at, not to decide direction.
• Check the same-day slice separately from the rest of the chain before comparing sessions.
• Re-read short-dated exposure through the day rather than treating an early reading as fixed.
• Keep the underlying price path in view, since exposure without price is an unchecked model.

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