I am trying to add the results of DATEIF

A1 1/1/12
A2 1/2/12

B4 =DATEDIF(A1,A2,"d")

But when I enter the next date, I get error #NUM! I realize it's looking for the next date but need to add the sum of B4:B10

Can anybody help. Can send excel spreadsheet if this helps.

Kind regards

Pedro