ISOWEEKNUM function in Excel takes a date as input and returns a week number (1-54).
ISOWEEKNUM Function in Excel is similar to WEEKNUM Function but it follows ISO standards, where weeks begin on Monday and week number 1 is assigned to the first week in a year that contains a Thursday.
Syntax for ISOWEEKNUM Function in Excel
date – The date for which you want to get the week number according to ISO standards.
Example of ISOWEEKNUM Function in Excel
ISOWEEKNUM Functions does not consider 1/1/2016 as First week of the year. It considers only from when the week starts with Monday and it should have Thursday in that week.
1/4/2016 which is Monday and has Thursday in that week, so 1/4/2016 is considered as first week. So the result will be
NOTE: ISOWEEKNUM function was introduced in Excel 2013 and so it is not available in earlier versions of Excel.