title: week of year starting at given date
body: <p>It's kind of hard to explain but I need to start counting weeks after a given date. Then I have to get the current date and check what week number it is.</p>
  
  <p>Already tried a few things and can't figure this out...
  Thanks!</p>
  
  <p>p.s. Maybe get the difference in days between two dates and divide by 7? How would I do this? </p>