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#Date and time

ISOWEEKNUM

Excel Functions

Get ISO week number for a given date

Syntax

EXCEL 
=ISOWEEKNUM(date)

Arguments

Parameter Description
date A valid Excel date in serial number format.

Return Value

A number between 1 and 54.

Details

The ISOWEEKNUM function returns a week number based on ISO standards. Under this standard, weeks begin on Monday and the week number 1 is assigned to the first week in a year that contains a Thursday, following ISO 8601. ISOWEEKNUM takes just one argument, date, which must be a valid Excel date. In the example shown, the formula in D5, copied down, is: The formula in E5, copied down the table, is: By default the standard WEEKNUM function will start week number 1 on the first day of the year, then increment week numbers on Sundays after that. The ISOWEEKNUM function increments on Mondays, and starts week 1 on the first week that contains a Thursday.

Examples

Examples

In the example shown, the formula in D5, copied down, is:

EXCEL 
=WEEKNUM(B5) // default week number
Examples

The formula in E5, copied down the table, is:

EXCEL 
=ISOWEEKNUM(C5) // ISO week number
Examples

The WEEKNUM function can also be configured to output an ISO week number, by setting the return_type argument to 21. The formula below will output the

EXCEL 
=WEEKNUM(B5,21) // ISO week number

See Also

WEEKNUM