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ISOWEEKNUM function in Google Sheets

Returns the number of the ISO week of the year where the provided date falls.

=ISOWEEKNUM(date)

ISOWEEKNUM syntax and parameters

One argument, one required.

  • dateanyRequired

    The date for which to determine the ISO week number. Must refer to a cell containing a date, number, or function returning a date type.

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 Excel

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.

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Related functions

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