How this calculator works
Enter number of trials, exact successes, success probability. CalcStack applies the displayed formula and reports each intermediate planning value with the units shown.
Formula / method
P(X=k) = C(n,k)p^k(1−p)^(n−k)
Worked example
Exactly 8 successes in 20 trials with p=0.4 has probability about 0.1797.
Assumptions and limitations
Trials are independent with constant success probability.
This does not calculate cumulative probability and is unsuitable for dependent trials.