Skip to content
ExcelExcel 2013+

ISOWEEKNUM function in Excel

Returns the number of the ISO week number of the year for a given date

=ISOWEEKNUM(date)

ISOWEEKNUM syntax and parameters

One argument, one required.

  • datenumberRequired

    Date is the date-time code used by Excel for date and time calculation.

ISOWEEKNUM examples

Formulas you'll actually reuse.

  1. The ISO 8601 week of an invoice date (weeks start Monday):

    =ISOWEEKNUM(B2)

    Result33

  2. 1 Jan 2027 is a Friday, so ISO puts it in week 53 of the previous year:

    =ISOWEEKNUM(DATE(2027, 1, 1))

    Result53

ISOWEEKNUM in Google Sheets

Same name — your formula ports as-is.

Try ISOWEEKNUM in the playground

Edit the example — nothing to install.

Preloaded with the ISOWEEKNUM formula from Example 1 — change anything and watch it respond.

Loading the editor…

Related functions

More ways Excel gets this done.