How to find out the number of the week in a calculated field?

Question

How can I calculate the number of the week based on a date in a list? I tried several examples I found on the internet, but none worked correctly?

The formula should comply with the ISO standard where the week always begins on a Monday, and ISO week 1 begins on the Monday of the first week of the year that contains a Thursday. Said differently, ISO week 1 is the first week (beginning on Monday) that has at least four days.

Anybody has a good solution for that?

Answer 1

I used the following formula. Week starts on monday. Depending on your regional settings you have to replace the ; with ,

=IF(INT((StartDate-DATE(YEAR(StartDate);1;1)+(TEXT(WEEKDAY(DATE(YEAR(StartDate);1;1)-1);"d")))/7)=0;52;INT((StartDate-DATE(YEAR(StartDate);1;1)+(TEXT(WEEKDAY(DATE(YEAR(StartDate);1;1)-1);"d")))/7))

Answer 2

On the following link a solution is described:

http://www.petestilgoe.com/2009/08/displaying-the-week-number-using-a-sharepoint-calculated-column/

Please keep in mind that different countries handle weeknumbers differently: week 1 could be: * the week of 1 january (any day) * the first week that has at least 4 days of januari * the first week that has 7 days of januari