The normal method in calculating Anticipated Losing Sequence remembering your calculating the confidence level not the actual amount of Losing turns, so to calculate to a 99% confidence level you use the following formula, 1 minus( Losing Strike Rate % (to the power of) ^ Losing turns )
eg if my win strike rate was 25% my losing S/r is .75
1-(.75^ 5)=76.3%
that is after 5 losing runs the confidence level is 76.3%, when you reach the first 99% that is your anticipated longest losing sequence.