One of the easier formulas I am using is from this post:
Maximum Drawdown in Trading Computation
This is the formula for maximum losing streak with the probability of happening at 1 per 10,000 trades:
Max = -4 /Log(L)
Where L is the loss probability of the trading system.
Supposing you have a 60% loss probability, then the maximum losing streak is:
Max = -4 /Log(0.6)
The logarithm is to the base 10, computing it would reveal:
18 consecutive losses.
The interesting to note is that the probability of occurrence for this 18 consecutive losses is only 1 out of 10000 trades. That's rare isn't it?
Now for those who are looking "formula for the probability of further losing streaks". It would mean computing for a drawdown that would occur at a much common probabilities, something like 1/100 or even 1/10
The math will be (supposing you would be interested to know what is the drawdown at 1/10 probability):
Let D be the drawdown and L be the loss probability of the trading system:
Converting to exponential function:
L^D = 1/10
Taking logarithms in both sides:
Log(L^D) = Log(1/10)
D*Log(L) = -1
Solving for drawdown at 1/10 probability (the logarithm is now in base 10):
D = -1 /Log(L)
Looking back at the above example, what is my "usual" or "high probability occurring" consecutive losses (estimated at 1/10 probability) if my system has 60% loss probability?
D= -1/Log(0.6)
The answer is around 5 consecutive losses. To minimize consecutive losses, its much better to reduce the %loss probability or having a high winning trading system.
Hope this post clarifies everything. I would be interested if someone could run an actual simulation as the above is plainly theory.