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?
You are now on the second two-week period so yes you will be jr.member by 2nd February (42 activity)