Syntax. WEEKNUM(serial_number,return_type)
Definition. This function returns an integer for the week number for the given date.
Arguments
serial_number (required). The date for which the week number is calculated.
return_type (optional). A number indicating on what day the week begins. This argument has the different options depending on the version of Excel you are using. In Excel 2003 and earlier, there are two return types:
1. System 1 (the default setting): The week begins on Sunday. The weekdays have the numbers 1 through 7, starting on Sunday.
2. System 2: The week begins on Monday. The weekdays have the numbers 1 through 7, starting on Monday.
In Excel 2010, the System 1 return type offers further options:
1. System 1 (default setting): The week begins on Sunday.
2. System 1: The week begins on Monday.
11. System 1: The week begins on Monday.
12. System 1: The week begins on Tuesday.
13. System 1: The week begins on Wednesday.
14. System 1: The week begins on Thursday.
15. System 1: The week begins on Friday.
16. System 1: The week begins on Saturday.
17. System 1: The week begins on Sunday.
21. System 2: The week begins on Monday.
Background. A year is divided into consecutively numbered weeks. There are two types of calculations in the WEEKNUM() function: In System 1, the week in which January 1 appears is considered as week number 1. In System 2, the week in which the first Thursday of the year appears is considered as week number 1. System 2 is the European week numbering system. The first day of week 1 is specified by the International Standards Organization (ISO) definition. System 2 is regulated by the ISO 8601 standard established in 1988.
See Also
For more information about saving dates in Excel, see the section titled The Excel Date System in Chapter 2.
Example. You may want to display the week number for each date in an operation schedule in Excel. To do this, use the formula
=WEEKNUM(date)