Description of US Stock Exchange Practices
Why is my limit or market orders not done when market opens at 9.30am (EST) and why is my executed price different from the opening price shown on POEMS?
All the orders received prior to market open will be routed and protected versus the stock’s primary listing exchange market opening print. Sometimes, there may be a delay in the opening for certain stocks in the primary exchange which will result in these counters not being able to open at 9.30am sharp.
However, you may still see transactions execute off the primary exchange before the official open, which by themselves are still required to be reported under SEC regulation. Any activity prior to the primary market open that is reported to the tape would be from alternative display facilities or dark pools. The reason that these trades are still reported to the tape, even though the primary market is not opened, is because under SEC rules, every stock transaction must be reported to a consolidated data feed, whether it occurs on an exchange, like the Nasdaq or Intercontinental Exchange Inc’s (ICE.N) New York Stock Exchange (NYSE), or in a dark pool. Off-exchange trades are reported through Trade Reporting Facilities (TRFs) run by Nasdaq and NYSE in conjunction with FINRA.
Similarly, the high and low of the day for certain counters may be executed off the primary exchange and may not be taken as official primary executed prices