### WEEKNUM(serial_num [,return_type])

Returns the week number in the year for a given date.

 serial_num The date within the week. return_type (Optional) The number that specifies on what day the week begins:1 = Sunday (default)2 = Monday11 = (Added in 2010) Monday (1 to 7)12 = (Added in 2010) Tuesday (1 to 7)13 = (Added in 2010) Wednesday (1 to 7)14 = (Added in 2010) Thursday (1 to 7)15 = (Added in 2010) Friday (1 to 7)16 = (Added in 2010) Saturday (1 to 7)17 = (Added in 2010) Sunday (1 to 7)21 = (Added in 2010) Monday (1 to 7)

#### Remarks

 * This function returns a number between 1 and 54.* If "return_type" is left blank, then 1 is used.* If "return_type" = 1, then weekdays are numbered Sunday = 1 to Saturday = 7.* If "return_type" = 2, then weekdays are numbered Monday = 1 to Sunday = 7.* This function is based on the American standard which considers the week containing January 1st to be the first week of the year.* The European convention however defines the first week as the first one containing four or more days.* If "return_type" = 21, then the weekdays according to the European Standard are returned.* You can use the DATE function to return the date serial number given a year, month, day.* You can use the ISOWEEKNUM function with return_type 21.* You can use the WEEKDAY function to return the day of the week.* You can use the WEEKNUMBER - User Defined Function if you want to use a VBA function.* In Excel 2007 the accuracy of this function was improved.* For the Microsoft documentation refer to support.microsoft.com

 A 1 =WEEKNUM("1/10/1999",1) = 40 2 =WEEKNUM("1/10/1999",2) = 40 3 =WEEKNUM("1/7/1977") = 27 4 =WEEKNUM("1/7/1977",1) = 27 5 =WEEKNUM(DATE(7,2,2005)) = 31 6 =WEEKNUM(TODAY(),30) = #NUM! 7 =WEEKNUM(invalid_namedrange) = #NAME?