Rank based on date for each individual user

Hello all,

I am trying to write a measure or column (whichever one does the trick) that ranks the due date for each individual in the table based on his or her respective due dates. For example, I have this table below. Whenever I try to rank their due dates I get an overall rank (see rank column) . What I am looking for is what's in the rankx column. A rank of due date for each customer only. 

Any ideas on how I can do this?