An example, if I registered on 11-01-2014, the next period would start on 25-01-2014?
You are wrong read again https://bitcointalksearch.org/topic/forum-rankspositionsbadges-what-do-those-shiny-coins-under-my-name-mean-178608
time = number of two-week periods in which you've posted since your registration
activity = min(time * 14, posts)
The activity will be calculated from your registration time but it will increase after each two week periods(dates are mentioned in above link).