Returns the ISO week number of the year where the provided date falls.
ISOWEEKNUM(DATE(1969, 7, 20))
- date - The date for which to determine the ISO week number.
ISOWEEKNUM("7/9/2019") returns 28 - the ISO week number of the year corresponding to 7/9/2019.
- As per ISO 8601:
- Weeks begin on Monday and end on Sunday.
- Week 1 of the year is the week containing the first Thursday of the year.
- As a result, if the first Thursday is after January 4, at least one of the following days, January 1-3, will have an ISOWEEKNUM of 52 or 53.
- Similarly, if the first Thursday is before January 4, at least one of the following days, December 29-31, will have an ISOWEEKNUM of 1.
- If the first Thursday is January 4, December 29-31 of the previous year will have ISOWEEKNUM of 52 and January 1-7 of the current year will have ISOWEEKNUM of 1.
- Problems can occur if dates are entered as text. You can use the DATE function to enter a date. For example, use DATE(2020,2,3) for the 3rd day of January, 2020.