There are SPX index options that expire every single day now (Mondays, Tuesdays, Wednesdays, Thursdays, and Fridays). I know that SPX options will trade until 4:00pm ET on the day of expiration. However, on days before the expiration day, they will trade until 4:15pm ET.

On days before the expiration day, how are prices set for SPX options between 4:00pm and 4:15pm when the value of the underlying SPX index doesn't change between 4:00 and 4:15?

  • Why would the SPX not change after 4?? All shares in it get still traded (until 7:30pm), so the index will also change.
    – Aganju
    Jun 28 at 22:06
  • It's true that the individual companies in the index still trade after 4, but the index itself stops updating at 4. It seems strange that options would continue to trade during a period when the underlying component is not updating.
    – 7529
    Jun 28 at 22:52


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