WEEKNUM

Returns a number representing the week of the year where the provided date falls.

Sample Usage

WEEKNUM(DATE(1969, 7, 20), 1)

WEEKNUM("12/09/1948", 2)

WEEKNUM("6/14/2002")

Syntax

WEEKNUM(date, [type])

• date - The date for which to determine the week number. Must be a reference to a cell containing a date, a function returning a date type, or a number.
• type - [ OPTIONAL - default is 1 ] - A number representing the day that a week starts on as well as the system used for determining the first week of the year (1=Sunday, 2=Monday).

Notes

• When inputting the date, it is best to use the DATE function, as text values may return errors.
• Behind the scenes, there are two week numbering "systems" used for this function:
  • System 1 - The first week of the year is considered to be the week containing January 1, which is numbered week 1.
  • System 2 - The first week of the year is considered to be the week containing the first Thursday of the year, which is numbered as week 1. System 2 is the approach specified in ISO 8601, also known as the European system for numbering weeks.
• For each type, the start day and end day of a week are defined as follows when counting week numbers:

  type	Day week begins on	Day week ends on	System
  1 or omitted	Sunday	Saturday	1
  2	Monday	Sunday	1
  11	Monday	Sunday	1
  12	Tuesday	Monday	1
  13	Wednesday	Tuesday	1
  14	Thursday	Wednesday	1
  15	Friday	Thursday	1
  16	Saturday	Friday	1
  17	Sunday	Saturday	1
  21	Monday	Sunday	2

See Also

WEEKDAY: Returns a number representing the day of the week of the date provided.

DAYS360: Returns the difference between two days based on the 360-day year used in some financial interest calculations.

DATE: Converts a year, month, and day into a date.

DATEVALUE: Converts a provided date string in a known format to a date value.