I thought this thread was going to be simple. But fortunately I did a little research and came to realize that many ET members regard overtrading as something that didn't even occur to me. Much to my surprise, it turns out that "overtrading" is an ambiguous word. I regard it as trading too large a size, i.e., trading too large a percentage of your account. But many (most?) here regard it as "trading just for the sake of trading", i.e., trading too frequently. That's cool, language can be ambiguous and I'm a flexible guy. But this is the Trading Management forum, not the Psychology forum, and people who trade too frequently are what I call trading addicts, not overtraders. So this thread isn't for members with discipline problems or emotional problems that lead to some trading addiction, this is for those who have discipline and a plan that works, i.e., yields positive expectation. So the question is, when are you trading too much size? More specifically, given that you have a trading system with positive expectation, you also have an optimal trading fraction (hereafter referred to as your "Kelly fraction") which most likely is unknown to you. The reason for the unknowing is that outside of the fairyland examples of biased and/or uneven-payoff coinflips, the Kelly formulas are only approximations. But let's assume that you could find a formula that consistently fell within a range of your true Kelly fraction. What would this range be, ideally or acceptably? Oh yeah, the "other thing" in the title is undertrading : when are you trading too little size? I previously posted that ideally I wanted something consistently between 90% and 100% of the Kelly fraction, but that works out to 95% Â± 5%. Now I think a more realistic goal might be 100% Â± 5%. So is 105% of Kelly overtrading? Not to me but YMMV. So what is an acceptable range of trading fraction values for you?