I know the activity is calculate in below formula:-
time = number of two-week periods in which you've posted since your registration
activity = min(time * 14, posts)
However, I registered on 12-Jan, last Tues, why I got 28 activity i/o 14 now?
so when will I promote to Jr. Member? 2-Feb?
January 19 is the date when activity points was awarded to those who reached substantial posts in this forum in which you did, next activity increase will be by February 2 and you'll be Jr member by that time.