Have you tired WeeksAgo (see comment by Alex)
As I'm very new to Qlikview, this is a great help. One question though, how would I create a WeeksAgo calendar field? My best guess was
52*(Week(Today())-Week(TempDate)) + Week(Today()) - Week(TempDate) as WeeksAgo
but this doesn't seem to work
The Week() function "restarts" at 1 every year, so you cannot use this if the two dates span two years. No, I would probably do
(WeekStart(Today()) - WeekStart(Date))/7
instead. To understand what this does you need to understand how QlikView handles dates. Read about this here. But to make a long story short: The WeekStart() function returns an integer corresponding to the day. So by taking the diff and dividing by 7, you get the number of weeks ago.