The ISOWEEKNUM returns the number of ISO week of the year if a date is provided. For example, the formula =ISOWEEKNUM(“12 Dec 2019”) returns 50, which means the given date is in 50th week of ISO week of the year.
date – Required. The date from which to get the ISO week of the year.
The ISO week year has 52 to 53 weeks depending on a leap year. The first week is referred as 1 and each week starts on Monday.
The #NUM! error will result if the given date is not a valid number. For example, the formula =ISOWEEKNUM(“Jan 1800”) results the #NUM! error.
The #VALUE! error will result if the given date is in invalid format.