How to rank week numbers beginning from your first date in Reporting Period

Hi,

I'm looking at weekly sales and I have data from one year (RP) and previous year (CP). Now I might have to do this more than once and as I start my RP 2/2010-1/2017 I would like to put week number in right order: so first week would be week 5 then six and so on.

Does anyone have answer how I could do this?

Thanks for your answer.

Best regards

-K-