I remember seeing similar activity calculator few years, but now I can't find, maybe it doesn't works anymore. After release of merit system, activity isn't such important thing anymore, but it's still interesting to check estimated date when you can rank up. So, thanks for making it.
One fun thing related to this topic - theymos told that I would have received Legendary status at lowest possible activity. So, I was just one week away from Legendary rank when merit system was released lol.