Every day, a stock or ETF has an official open price, like its high, low, and close prices. If I put in a market-buy-at-open order, whether well before the open (overnight) or just a minute or two before the open, I sometimes get the official open price, but often not, sometimes by a significant amount. Apparently the open price is set by the open auction, aka opening cross, but the official open price is from the first trade of the day after the market opens. If I sell at close, I (almost) always get the official close price, but not so for the open. Anyone know why, or how to get the official open price consistently?

Edit: For reference, the auction I'm talking about is described here:

And the questions I'm trying to resolve are related to http://www.elitetrader.com/et/index.php?threads/where-can-i-check-nyse-opening-auction-prices.286797/

  • The answer here is clearly wrong. I wonder if you ever resolved this question? – user1175 Apr 5 '17 at 4:09

There is no official price. There is only the price a seller is willing to offer and a buyer is willing to accept at that moment. It tends to be close to the price negotiated for the last such sale, but that's just market statistics, not anything actively managed or guaranteed. "Past performance is no guarantee of future results;" this buyer and seller may not agree with the previous pair. Especially when the market has been closed overnight but real-world events have continued to occur.

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    If you go to any of the financial sites, you will find that ABC opened at $x.yz, just as it had a high, low, and close price. The open price is set by an auction process before the open. I'm afraid your answer does not address my question. – Albert Leo Jul 20 '15 at 13:35
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    You can't get that "official open price" unless someone is willing to sell for that price or less. As far as I know, it is entirely a statistical fiction intended only as a suggested/best-guess starting point so folks can factor it into their plans. It is not in any way a guaranteed or enforced price. – keshlam Jul 20 '15 at 14:33
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    Sorry I wasted my time here. – Albert Leo Jul 21 '15 at 5:12
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    Took the liberty of editing these into your question. Comments on SE don't always persist, and a self-contained question is more useful for future readers. – keshlam Jul 25 '15 at 3:31

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