Calculate bi-weekly weeknumbers

[IwanGerbes]

For an excel, i need to automatically calculate the bi-weekly numbers. So for 2018, up till 5 January 2018 is week #1 , from 6 till 19 January is week #2 , from 20 Jan till 2 Feb is week #3 .
With the formula WEEKNUM i only get the real weeknumbers. Is there an easy formula to do this, or do i really have to calculate it in a complex formula per calendar year?

 

[SteveO59L]

possibly make a list of your date and associated week number, then use vlookup()?