The `WEEKNUM` function in Excel is used to determine the week number of a specific date. The week number is commonly used in calendar management to track and compare week-to-week activities or events.
Here’s how to use the `WEEKNUM` function:
Syntax
WEEKNUM(serial_number, [return_type])
- `serial_number`: This is a required argument. It is the date for which you want to find the week number. You can enter a date directly by using a date string, or by using a cell reference containing a date.
- `return_type`: This is an optional argument. It specifies which day the week starts on, and therefore determines how the week numbering is calculated.
Available Return Types
- 1 or omitted: Week starts on Sunday. It uses the system where the first week of the year is the week that contains January 1st.
- 2: Week starts on Monday. It uses the system where the first week of the year is the week that contains January 1st.
- 11: Week starts on Monday. It uses the ISO-8601 system, where the first week of the year is the week that contains the first Thursday of the year (often used in European countries).
- Other values: There are several other return types (setting different days as the start of the week), but these three are the most commonly used.
Example
If you want to find out which week number October 4, 2023, falls on in a system where the week starts on Monday, you would enter:
=WEEKNUM("2023-10-04", 2)
If you have the date in cell A1, you would enter:
=WEEKNUM(A1, 2)
Important Points
- Ensure the date argument is in a valid format or a recognized date to prevent errors.
- Results may differ depending on the regional settings and the return type used.
- Starting with Excel 2010, the function supports ISO week numbers when using return type 11.
Make sure your dates are correctly formatted and that you consider which type of week numbering makes sense for your application (standard vs ISO).
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