WeekNum

Description of formula:
Calculates week number in year, returns number from 1 to 53.

Syntax:
weeknum(date, [mode])

Parameters:
 

date

(type: Date) date to calculate week number form.

mode

(type: Number) you can choose whether the week starts from monday or sunday: 1 - week begins with sunday, 2 - week begins with monday, 1 is default value.

Returned type:
 

Number

Examples:
=weeknum(A1)
=weeknum(A1, 1)
=weeknum(Date(2026,1,1), 2)

 

How we calculate week numbers in a year.

The rule is that the first week of the year always starts on 1 January and ends on the last day of the week (depending on the mode adopted). Therefore, if 1 January falls in the middle of the week, the first and last weeks may be shorter than seven days.