The ISOWEEKNUM function accepts a date and returns theISOweek number (1 through 54) of that date. The date must be in avalid format, so you have to use theDATE function, wrap it in quotes, or use a cell reference to a cell containing a date.

An ISO week starts on Monday. The first week of the year is the first week containing a Thursday in that year.

If your days, months, and years are in different cells, use theDATE functionto combine them.



  • date- The date for which you want the ISO week number. This is required.

Related functions

DATE- Takes separate year, month, and day values and returns them as a date

DATEVALUE- Returns the serial value of a date

WEEKNUM- Returns the number of a given week


#NUM- The inputs are numbers but are not valid dates. This could happen if you used the 35th day of November.

#VALUE!- The inputs are something that doesn't convert to a number such as "The other day" or "Yester-yester-day".


Example 1 - Plain and Simple

=ISOWEEKNUM("March 1,2017")9

Example 2 - ISOWEEKNUM withDATEfunction



 Live examples in Sheets 

Go tothis spreadsheetfor the examples of the ISOWEEKNUM function shown above that you can study and use anywhere you would like.