Determining Position Size

Before beginning any trading program, an assessment should be made of the maximum account loss that is likely to occur over time, per lot (see "Drawdown" in "Glossary of Terms"). For example, assume you have determined that your worse case loss on any trade is 30 pips. That translates into approximately $300 per $100,000 position size. Further assume that the $100,000 position size is equal to one lot.

Five consecutive losing trades would result in a loss of $1,500 (5 x $300); a difficult period but not to be unexpected over the long run. For a $10,000 account trading one lot, this translates into a 15% loss. Therefore, even though it may be possible to trade 5 lots or more with a $10,000 account, this analysis suggests that the resulting "drawdown" would be too great (75% or more of the account value would be wiped out).

Any trader should have a sense of this maximum loss per lot, and then determine the amount he wishes to trade for a given account size that will yield tolerable drawdowns.