0DTE Options: What They Are and the Share of Option Volume

0DTE options are options with zero days to expiration: contracts traded on the same day they expire. They can make up a large share of option volume in index ETFs and some heavily traded stocks. Vyreon measures the 0DTE share of each security's option volume for each session.

What Are 0DTE Options?

Every option has an expiration date. On that date its remaining time value runs out, so its price responds sharply to small moves in the underlying. A "0DTE" trade is any trade in a contract on its final day. Securities with daily expirations, such as major index ETFs, have a 0DTE contract every trading day. Securities with only weekly or monthly expirations have one only on those dates.

Why 0DTE Volume Can Exceed Open Interest

Open interest counts contracts still open at the previous close. For a same-day contract it can be small, because positions opened and closed within the session never appear in it. Volume counts every contract traded during the day, including positions opened and closed again before the close. So same-day volume can exceed the open interest at the start of the day, sometimes many times over. For a contract on its final day that follows from how the two are counted; it is not, on its own, a sign of unusual positioning.

This is also why Vyreon's unusual options activity measure excludes same-day expiries. Otherwise they would dominate it every day.

How Vyreon Measures It

0DTE share of volume: contracts traded today in options expiring today, divided by the security's total reported option volume for the session.
0DTE contracts traded: the same volume in contracts.
Same-day expiry listed: whether the security had an expiration today. When none is listed, the share is 0 and the report says that no same-day expiry existed, so a zero is never mistaken for a quiet day.
End-of-day: the measurement uses the session's final reported volume. It is not an intraday reading.

Illustrative example: a security trades 1,000,000 option contracts in a session, and 600,000 of them are in contracts expiring that day. The 0DTE share is 60%. A security with only monthly expirations would show 0% on most days and a spike on its expiration day.

Is 0DTE Trading Bullish Or Bearish?

Neither, as measured here. The share counts contracts in both calls and puts, whoever bought or sold them. A high share means much of the day's options activity was very short-term trading. It does not tell you which way that trading leaned, or whether it was speculation, hedging or market-making.

What It Does Not Tell You

It does not show direction, buyers versus sellers, or dollar amounts.
It is not a forecast of price movement or volatility.
It does not describe intraday timing, such as when during the session the 0DTE volume traded.
Shares are comparable over time for one security, but differ structurally between securities with daily expirations and those without.

Sources

The Options Clearing Corporation (OCC), Characteristics and Risks of Standardized Options, the options disclosure document: expiration and how listed options work.
John C. Hull, Options, Futures, and Other Derivatives (Pearson, many editions): time value and its decay toward expiration.

"0DTE" is a market term for any contract on its final trading day, not a separate type of contract; it has no single originator.