Contracts that expire on the same trading day. Theta accelerates sharply in the final hours, which hurts the buyer and helps the seller. Available on SPX, SPY and QQQ every trading day.
What these contracts are
0DTE (0DTE · Zero Days to Expiration) options trade on the day they expire. They are no longer a niche case: on the major indexes they are among the most actively traded contracts, because daily expirations made every session an expiration day for some contract.
Extreme mechanics
On expiration day, the gamma of at-the-money contracts swells to its maximum and theta is at its fiercest. Within hours the contract turns from time value into zero, or into its spot value. A half-percent move in the index flips an at-the-money contract from a loser to a double, and back. That is huge leverage in both directions, with no time to recover.
Its effect on the market itself
These contracts trade so heavily that market-maker hedging in them becomes an instant force inside the session. Positioning piled near a close strike pulls price toward it or throws it away, depending on the sign of gamma. So the one-day gamma map reads as a map of the session's forces, not just a list of contracts.
Hypothetical example
An index opens at 5,000 and a 0DTE call has a strike of 5,010 with a premium of $6. The index reaches 5,025 before the close: spot value $15 and a gain of about 150%. It stays below 5,010: a total loss. The two outcomes are half a percent apart.
Common mistake
Carrying weekly-contract habits over to them: there is no time to wait for a bounce, and theta gives no second chance. The size of position you can afford to lose entirely is the rule for handling them. A total loss is an ordinary outcome, not an exception.
Where to see it on the platform
The gamma board shows positioning at the nearest expiration along with both walls and the Gamma Flip. The flow tools show the premiums of these contracts as they stream in during the session.
