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Excel

WEEKNUM function in Excel

Converts a serial number to a number representing where the week falls numerically with a year

=WEEKNUM(serial_number, [return_type])

WEEKNUM syntax and parameters

Two arguments, one required.

  • serial_numbernumberRequired

    A date within the week. Dates should be entered by using the DATE function, or as results of other formulas or functions. For example, use DATE(2008,5,23) for the 23rd day of May, 2008. Problems can occur if dates are entered as text.

  • return_typenumberOptional

    A number that determines on which day the week begins. The default is 1.

WEEKNUM examples

Formulas you'll actually reuse.

  1. The calendar week of an invoice date (week 1 holds 1 January, weeks start Sunday):

    =WEEKNUM(B2)

    Result33

  2. 1 January is always week 1 here — unlike ISOWEEKNUM, which gives 53:

    =WEEKNUM(DATE(2027, 1, 1))

    Result1

WEEKNUM in Google Sheets

Same name — your formula ports as-is.

Try WEEKNUM in the playground

Edit the example — nothing to install.

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

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Related functions

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