The WEEKNUM Function is to return the week number with the date you specified.
- Serial_number is required. A date within the week which you are looking for. Serial number should be a date in Microsoft Excel format, the function will return to an error when it is in a wrong format, such as text format.
- Return_type is optional. A number that determines on which day the week begins, default is 1.
By default, Microsoft Excel uses January 1, 1900 as serial number 1. If a serial number or return type is out of the range, the result will return "#NUM!" error.