This post shows you how to use the date hierarchy and the grouping function to easily group your data by year, month, week in Power BI. This can be very handy when reporting against data that is timephased, such as sales transactions or Project Online schedule and capacity data.
If you need to start your week on a specific day of the week, you can create a new column based on your date, using this DAX statement:
Week Beginning Date = ‘TableName'[DateFieldName] – MOD(‘TableName'[DateFieldName]-1,7) + [Add 0 for Sunday, 1 for Monday, etc. to start week accordingly]