Calculating number of weeks between two dates from different year

Hi,

Situation is like this: Suppose i Have a drug data with its expiry date:

Exp. date is of different year.

Now I have another column with date, based on which I calculated the week number.

Now I have 2 slicer from this: Year and Weeknum.

When I select year as 2016 and week as 34 then I should get the name of drugs with their week to expiry data. (how many weeks remaining to expire the medicine)

I tried:  weeknum(exp) - weeknum(current date)

for same year (exp year = 2016) it is working fine for other years it is not working fine.

I am trying for a dynamic report where i can go to past or futer and figure out at tht time how many weeks were remaining for the drug to expire.

Meaning based on week slicer I should be able to see the data according to the week selected.

Thanks.. Please advise.