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(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).


  • 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.

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