An acronym for calculated opening price; the trading price where the most securities (e.g., shares) trade in a given market. In other words, it is the price intended to create the highest volume of trade at a given time interval. In the case where more than one price satisfies this condition, the calculated opening price (COP) is the price that leaves the minimum deal of imbalance. Still, if there is more than one price that satisfies these two conditions, the COP is the price closest to the previous day’s closing price.

Once the opening price is established, all the orders that can execute at this price will be filled. A the open, the aggressive side (bid or offer) is designated as the “balanced side”- that is, the side that will be completely traded in the open. When the bid volume and the offer volume are equal, both sides will be completely traded. Furthermore, the side with the earliest order (in terms of the time it comes to the market) will be designated as the aggressive side.

Typically, an auction order is submitted at the calculated opening price (COP). If the order is not filled, it will be resubmitted as a limit order at the COP or best bid-ask.