Many times I was asked to filter Task List by week number (e.g show this week task) .
In this post, I'll Explain how to calculate week number with SharePoint formula.
1. First step, create your SharePoint list and add calculate filed.
2. Add the following formula
=INT(([Start Date]-DATE(YEAR([Start Date]),1,1)+(TEXT(WEEKDAY(DATE(YEAR([Start Date]),1,1)),"d")))/7)+1
Formula description
= ({Calculate the distance between the begging of the year to the current date} + {the first day of the week in which the year begins})/ {Number of day per week} + {1}
Enjoy