I don't know how Lou Krieger does it, but if he uses the term "confidence interval", then I'm suspicious that he might be doing it wrong. It is a common mistake to say that because being broke represents a certain number of standard deviations below the mean after a certain number of hours, that this is your risk of ruin. The reason is that you can go broke before you ever reach this number of hours. This is not the way to do risk of ruin calculations. Use this formula to compute risk of ruin for a given bankroll:


r = [(1-u/sigma)/(1+u/sigma)]^(B/sigma)


u is hourly rate

sigma is hourly standard deviation

B is bankroll


This is correct, and comes from "Blackjack Attack" by Don Schlesinger. To get bankroll for a given risk of ruin, you can invert this equation or use:


B = [-sigma^2/(2B)]ln(r)