Forumla for reoccurance / countif

Hi everyone,

I am not the best person when it comes to excel. So I really dont know what formula I need.

This is my problem:

I have excel column "say A" and in this column I have ID numbers. After a manual check of over 522 ID's I noticed there are some duplicates (meaning same ID for two different people)

So what I like is a formula that alerts that theres a duplicate "number set" and maybe highlight or notify me some way. Also, this formula should also work when new entries are made as the list gets longer (ie: if I add a new entry and it so happens to be the same as another number above). I used been able to keep track, but the list is getting longer and longer by the day.

I feel like I am writing a software program, its that difficulate for me to do. So please explain in "baby terms" what I should do.


Thank you in advance for advice

MOB

Selecting as many cells in column A that you might need, starting in A2, then add conditional formatting with a formula of

=COUNTIF($A:$A,$A2)>1

and add a format fill colour.

How do I add colour fill options

It's an option in CF, press te format button, and fill is a tab after that.