The Impact of Slippage Commissions and Spreads on Your Trading Strategy

Back testing does not take into account slippage commissions and spreads. A lower time frame trader, they're going to have a bigger impact than someone that trades on the daily chart. If you trade in the daily chart, your slippage isn't going to be a big deal. But if you're trading on a range bar chart or a one minute chart, spread can be 50% of your profit target.