Tom’s Tutorials For Excel: Keep a Running Count of Duplicate Entries
In cases where duplicate entries are expected, you can easily keep a running count of each entry with a formula to tell you how many times the entry exists in your list. There is a number next to each entry to tell you how many times in the list that particular entry has thus far appeared.
In the picture, the formula
=COUNTIF($B$2:$B2,B2) is entered into cell C2 and copied down as needed. This method can be applied to lists that are typically comprised of the same entry, such as store purchases, or the types of computer errors your IT department corrects, or reasons for employee sick days.