Although this thread is 3 years old, I'll answer anyway. I use IB and trade ES. It's not 0.25 slippage. If you look at your trade report the execution price is the price traded. Almost always this is my limit price. However, the price in my account gets adjusted with the commission I paid. This is mostly 0.25 lower when shorting and 0.25 higher when long. They do this, so you know your profit/loss after costs. Also, when I used to trade stocks the adjusted price was a lot more than 0.25.