Calculating # of days early or late

Does anyone know of an easy formula that would look at two dates and figure out if the task is early or late and by how many days?

Example:

Estimated Date Due: 9/1/08
Actual Date Completed: 9/5/08
Days late = 4

Estimated Date Due: 9/10/08
Actual Date Completed: 9/5/08
Days early = 5

Assuming estimated date is in A1 and actual in B1 you could use this formula

=IF(B1="","",TEXT(B1-A1,"0 ""Day(s) Late"";0 "" Day(s) Early"";""On Time"""))

That's awesome. Now, what if there is no "actual date" (i.e. the task hasn't begun yet)? What happens now is this will show as something like 39707 Day(s) Early.

The formula I suggested should return a blank if B1 [actual date] is blank.

You could alter the formula so that it only shows a result when A1 and B1 both contain dates, e.g.

=IF(COUNT(A1,B1)=2,TEXT(B1-A1,"0 ""Day(s) Late"";0 "" Day(s) Early"";""On Time"""),"")

Thank you very much. That did just what I wanted.