# WEEKNUM function

Returns a number that indicates where the week falls numerically within a year.

Important    The WEEKNUM function considers the week containing January 1 to be the first week of the year. However, there is a European standard that defines the first week as the one with the majority of days (four or more) falling in the new year. This means that for years in which there are three days or less in the first week of January, the WEEKNUM function returns week numbers that are incorrect according to the European standard.

Syntax

WEEKNUM(serial_num,return_type)

Serial_num     is a date within the week. Dates should be entered by using the DATE function, or as results of other formulas or functions. For example, use DATE(2008,5,23) for the 23rd day of May, 2008. Problems can occur if dates are entered as text.

Return_type     is a number that determines on which day the week begins. The default is 1.

Return_type Week Begins
1 Week begins on Sunday. Weekdays are numbered 1 through 7.
2 Week begins on Monday. Weekdays are numbered 1 through 7.

Remark

Microsoft Excel stores dates as sequential serial numbers so they can be used in calculations. By default, January 1, 1900 is serial number 1, and January 1, 2008 is serial number 39448 because it is 39,448 days after January 1, 1900. Microsoft Excel for the Macintosh uses a different date system as its default.

Example

The example may be easier to understand if you copy it to a blank worksheet.

1. Create a blank workbook or worksheet.
2. Select the example in the Help topic.

Note   Do not select the row or column headers.

Selecting an example from Help
1. Press CTRL+C.
2. In the worksheet, select cell A1, and press CTRL+V.
3. To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.
A
Data
March 9, 2008
Formula Description (Result)
=WEEKNUM(A2,1) Number of the week in the year, with a week beginning on Sunday (11)
=WEEKNUM(A2,2) Number of the week in the year, with a week beginning on Monday (10)

Note   March 9, 2008 is a Sunday.

Applies to:
Excel 2007