Calculating percentage based on new data

Suppose on the attached sample I want to add new data for today 4/22/13 at column E. I insert a blank column at E which moves the percentage column to column F. At E1 I enter 4/22/13 and enter the proper numbers in rows E2-E10. How can the percentage be updated to reflect the new position of the added column?

I was looking at using the name function to so I can change the reference from column D to E but it needs to be a full cell reference, not a column reference.