I think that the 11th rank would require 4500 posts. Why? because rank 7 requires 750, rank 8 1000, rank 9 1500 and rank 10 2500. If you still haven't noticed, the difference doubles. 1000-750=250, 1500-1000=500 2500-1500=1000. then double the number and add that to your current rank. ( after rank 7) Still haven't noticed? 250,500,1500,2500,4500,etc... I think the rank 12 requires 8500.