It depends on how many activity period you were active.
Imagine you were active in two different activity period and posted once in each activity period. You are eligible to get 28 activities. Now, if you have posted in a lot of different activity periods for one/two or as many time as, you are eligible for YOUR ACTIVITY PERIOD*14 activities. I hope it is clear now.
I read your reply and it interests me. But I am not sure what I understood is actually what you meant. Permit me to say it the way I understood, and see if it's actually what you meant.
I registered an account today and made just one post. That means I am eligible for 14 activity addition every 14days. But due to I didn't make sufficient post, my activity will remain 1 (+13 unclaimed). Then, I wait again for another 14days and drop a post, I will have two activity (+13 and 13 unclaimed). So, after 1 month, if I begin to post frequently, I am entitled to 13+13 activity?