SQL UDF to get No. of Days in a Month

CREATE FUNCTION [dbo].[fn_GetNumDaysInMonth] ( @myDateTime DATETIME )

RETURNS INT

AS

BEGIN

DECLARE @rtDate INT

SET @rtDate = CASE WHEN MONTH(@myDateTime)

IN (1, 3, 5, 7, 8, 10, 12) THEN 31

WHEN MONTH(@myDateTime) IN (4, 6, 9, 11) THEN 30

ELSE CASE WHEN (YEAR(@myDateTime) % 4 = 0

AND

YEAR(@myDateTime) % 100 != 0)

OR

(YEAR(@myDateTime) % 400 = 0)

THEN 29

ELSE 28 END

END

RETURN @rtDate

END