Position Sizing

DEFINITION of 'Position Sizing'

Position sizing refers to the number of units invested in a particular security by an investor or trader. An investor's account size and risk tolerance should be taken into account when determining appropriate position sizing.

BREAKING DOWN 'Position Sizing'

Position sizing basically refers to the size of a position within a particular portfolio, or the dollar amount that an investor is going to trade. Investors use position sizing to help determine how many units of a security they can purchase which helps them to control risk and maximize returns. (For further reading, see: Optimal Position Size Reduces Risk.)

Position Sizing Example

Using correct position sizing involves three steps:

  • Determining Account Risk: Before an investor can use appropriate position sizing for a specific trade, they must determine their account risk. This typically gets expressed as a percentage of the investor’s capital. As a rule of thumb, most retail investors risk no more than 2% of their investment capital on any one trade; fund managers usually risk less than this amount. For example, if an investor has a $25,000 account and decides to set their maximum account risk at 2%, they cannot risk more than $500 per trade (2% x $25,000). Even if the investor loses 10 consecutive trades in a row, they have only lost 20% of their investment capital.                                                                                      
  • Determining Trade Risk: The investor must then determine where to place his or her stop loss order for the specific trade. If the investor is trading stocks, the trade risk is the distance, in dollars, between to intended entry price and the stop-loss price. For example, if an investor intends to purchase Apple Inc. at $160 and place a stop-loss order at $140, the trade risk is $20 per share.                                                                                                                                                                                                                    
  • Determining Proper Position Size: The investor now knows that they can risk $500 per trade and are risking $20 per share. To work out the correct position size from this information, the investor simply needs to divide the account risk, which is $500 by the trade risk, which is $20. This means 25 shares can be bought ($500 / $20).

Position Sizing and Gap Risk

Investors should be aware that even if they use correct position sizing, they may lose more than their specified account risk limit if a stock gaps below their stop-loss order. If increased volatility is expected, such as before company earnings announcements, investors may want to half their position size to reduce gap risk. (For more, see: Do Stop or Limit Orders Protect You Against Gaps in a Stock’s Price?)