WorksheetFunction.Fact (Excel)

Returns the factorial of a number. The factorial of a number is equal to 1*2*3*...

Fact (Arg1)

Arg1: Number - the nonnegative number that you want the factorial of. If number is not an integer, it is truncated.

Dim dblArg1 As Double: dblArg1 = 
Dim dblFact As Double
dblFact = WorksheetFunction.Fact(Arg1:=dblArg1)