Returns the cumulative beta probability distribution function. The cumulative beta probability distribution function is commonly used to study variation in the percentage of something across samples, such as the fraction of the day people spend watching television.
Syntax
BETADIST(x,alpha,beta,A,B)
X is the value between A and B at which to evaluate the function.
Alpha is a parameter to the distribution.
Beta is a parameter to the distribution.
A is an optional lower bound to the interval of x.
B is an optional upper bound to the interval of x.
Remarks

If any argument is nonnumeric, BETADIST returns the #VALUE! error value.

If alpha ≤ 0 or beta ≤ 0, BETADIST returns the #NUM! error value.

If x < A, x > B, or A = B, BETADIST returns the #NUM! error value.

If you omit values for A and B, BETADIST uses the standard cumulative beta distribution, so that A = 0 and B = 1.
Example
X 
Alpha 
Beta 
A 
B 
Formula 
Description (Result) 
2 
8 
10 
1 
3 
=BETADIST([X],[Alpha],[Beta],[A],[B]) 
Cumulative beta probability density function, for the parameters (0.685470581) 