The FACTDOUBLE is a Math function that returns the double factorial of a given number. Also known as the semi-factorialdouble factorial of a number (n) is shown as n!! and is equal to n x (n-2) x (n-4) x ... 4 x 2 for an even number, and n x (n-2) x (n-4) x ... 3 x 1 for an odd number. This denotation is typically used for simplifying some more complex expressions. In this guide, we’re going to show you how to use the FACTDOUBLE function in Excel, and also go over some tips and error handling methods.

Supported versions

  • All Excel versions

FACTDOUBLE Function Syntax




A number greater than or equal to -1 to calculate the factorial of


Common Scenarios

The double factorial of a number is the product of all the integers from 1 up to n that have the same parity (odd or even) as the number. For example,

=FACTDOUBLE(5) returns 15 (=5*3*1)

=FACTDOUBLE(6) returns 48 (=6*4*2)

Other Scenarios

You can't calculate the double factorial of a negative number less than -1, or a decimal number in mathematics. While negative numbers less than -1 will give a #NUM! error, decimal numbers will be truncated.

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  • If any argument values is not an integer, it will be truncated.
  • Use the FACT function to calculate the factorial (n!) of a number.


  • If any argument is a negative number less than -1, the FACTDOUBLE function returns a #NUM! error.