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I have an stock brokerage account at TD Ameritrade, and I noticed that it allows market-on-close (MOC) and limit-on-close (LOC) orders, but not market-on-open (MOO) and limit-on-open (LOO) orders. Is there a reason why a stock brokerage firm has support for trading at the close but not at the open? Is the opening auction somehow more expensive for brokerage firms?

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  • Have you asked TD Ameritrade? – base64 Apr 24 at 13:51
  • @base64 They did not supply a reason. They merely confirmed that they do not support on-open orders, and suggested that I place regular limit orders instead. From what I gather from forum posts around the world wide web, this has been the case for many years now. – Flux Apr 24 at 13:54
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    What difference does the reason make? – quid Apr 24 at 14:28
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    @quid "What difference does the reason make?" No difference. I am asking the question out of curiosity. It seems a bit odd that the closing auction is supported, but not the opening auction. – Flux Apr 24 at 14:33
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If I understand everything correctly, TD Ameritrade does support market-on-open orders. Simply submit a market order while the market is closed, and it will be executed as a market-on-open order when the market opens.

In order to try to verify this, I looked at the fill prices of a couple of market orders I placed while the market was closed. I looked at two buy orders on different days, and both of them executed at that day's opening price listed on Yahoo Finance. I also looked at one sell order, and it executed at a price one cent better (higher) than that day's opening price.

It also seems to be possible to do a limit-on-open order by submitting a limit order with a fill-or-kill instruction while the market is closed. Presumably, when the market opens, if the opening price satisfies the order, then the order will be filled at that price, and if the opening price does not satisfy the order, then the order will be canceled.

Just now, I verified that it is possible to place such an order, but I have not confirmed that such an order will actually behave as expected.

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