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

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?

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))

• about the regional settings: login with browser locale "en-us". then add this formula in a calculated field, save it. After that,change back the locale ID and the formula automatically replaces with the localized formula. Jul 14 '11 at 16:18
• Hi Can you suggest me what changes i need to make if my week starts from Sunday rather than Monday, and First week would be the week having Wednesday Nov 11 '16 at 5:24
• @Flash265 Is it possible to let us know what to change to get it to start from Sunday? Mar 5 '19 at 18:54
• I found that this formula from @Flash265 works quite well but skips 1 week. For example, running it against 01/jan/2019 returns 52 whether it should return 1. Also, for 31/12/2019 it returns 52 too whether it should return 53. I did this tests running the results against the WeekNum() function on excel, so I've made a little change to it in order to fix that. Here my version: =IF(INT((StartDate-DATE(YEAR(StartDate);1;1)+(TEXT(WEEKDAY(DATE(YEAR(StartDate);1;1)-1);"d")))/7)=0;1;INT((StartDate-DATE(YEAR(StartDate);1;1)+(TEXT(WEEKDAY(DATE(YEAR(StartDate);1;1)-1);"d")))/7)+1) May 14 '19 at 15:04

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

• The formula under your link does not seem to work correctly: For example: for 1/1/2012 it returns week 4. It's seems to work for 2011 and 2013, 2014. But not for 2012. Strange. Jul 14 '11 at 9:57
=INT(([Report Date]-DATE(YEAR([Report Date]),1,1)+(TEXT(WEEKDAY(DATE(YEAR([Report Date]),1,1)),"d")))/7)+1
• Please provide a descriptive answer so it will be useful to the forum. Mar 15 '16 at 3:24