In the previous lesson we talked about the martingale and anti-martingale methods of trading which are the two categories which position sizing methodologies fall into. In today’s lesson we are going to talk about one of the most basic anti-martingale strategies, which is discussed in Dr. Van K. Tharp’s book Trade Your Way to Financial Freedom, the Percent Risk Model.
The first step in determining your position size using this method is to decide how much you are going to risk on each trade in terms of a percentage of your trading capital. As we have discussed in our previous lessons on setting stop losses, studies have proven that over the long term traders who risk more than 2% of their capital on any one trade normally are not successful over the long term. Another factor to consider here when setting this percentage are things such as the win rate (how many winning trades) your stock, futures, or forex trading strategy is expected to have versus the number of losing trades as well as other components which we will discuss in future lessons.
Once this loss in percentage terms has been determined, setting your stop then becomes a function of knowing how large a position can be traded while still being below your maximum risk level.
As an example lets say you have $100,000 in trading capital and you have determined from analyzing your strategy that 2% or $2000 (2%*$100,000) of your trading capital is an appropriate amount to risk per trade. When analyzing the Crude Oil Futures market you spot an opportunity to sell crude at $90 a barrel at which point you feel there is a good chance it will trade down to at least $88 a barrel. You have also spotted a strong resistance point at just below $91 a barrel and feel that 91 is a good level to place your stop and also gives you a reward to risk ratio of 2 to 1.
From trading crude oil you know that a 1 cent or 1 point move in the market equals $10 per contract. So analyzing further to determine your position size you would multiply $10 times the number of points your stop is away from your entry price (in this case 100) and you would come up with $1000 in risk per contract. Lastly you divide the total dollar amount you are willing to risk by your total risk per contract ($2000 total risk/$1000 risk per contract) to get the number of contracts which you can place on this trade (in this case 2 contracts)
As Dr. Van K. Tharp points out in his book Trade Your Way to Financial Freedom, the advantages of this style of position sizing are that it allows both large and small accounts to grow steadily and that it equalizes the performance in the portfolio by the actual risk. As he also points out the disadvantages of this system are that it will require you to reject some trades because they are too risky (i.e. you will not have enough money in your account to trade the minimum contract size while staying under your maximum risk level) and that there is no way to know for sure what the actual amount you are risking will be because of slippage which can result in dramatic differences in performance when trading larger positions or using tight stops.
That completes our lesson. In the next lesson we will look at another position sizing model which is known as the Percent Volatility Model.