Equity, single-leg option, and multi-leg option trades can receive price improvement. Equity and single leg option orders that are executed while the market is open will display an estimate of the total dollar value of price improvement that you received, if any, based on the bid ask at the time your order was submitted. If your order is not immediately marketable, for instance if you place a limit or stop order away from the current bid ask, the price improvement indication will not be displayed. This is because as seconds or minutes pass, market conditions change, and your execution price is more a reflection of those changing conditions than it is of true price improvement.