To my mind, it would be better to calculate risk according to the average daily profit. The idea is that maximum daily loss should not exceed the half of average daily profit. Then you can divide this amount into the number of position you may have during the day in accordance with your trading system. For example, if your average daily profit is $100, your maximum loss per day should be $50. If the average number of trades per day is up to 5, then your risk per trade should be $10. This is very simple calculation without taking fees into account, but if the idea itself seems interesting and useful, you can improve it depending on your particular trading style. Such approach to risk management helps trader to avoid psychological pressure caused by huge daily loss, because it would be quite easy to recover after maximum daily loss - it would take only one day. Newbie traders that have no track of records should just start with the lowest position sizr available and then make those calculations based on their performance for a few weeks. The method described above is widely used among active daytraders. It could be also used for other trading styles just with minor changes and amendments.