# Duplicates within a calendar week

#### IRJULIE

##### New Member
Hi everyone!

First time posting here so please excuse my ignorance...

I am trying to find a formula or conditional formatting option to highlight rows of duplicate data that occur within a calendar week (Monday-Sunday). I have only 2 columns of data; column A is a serial number and column B is a date. All dates fall within the same month and each serial number should occur once in each calendar week for the month (though occasionally not for every week).

 Serial A 3/11/2020​ Serial A 10/11/2020​ Serial A 17/11/2020​ Serial A 24/11/2020​ Serial A 25/11/2020​ Serial B 4/11/2020​ Serial B 11/11/2020​ Serial B 18/11/2020​ Serial B 20/11/2020​ Serial B 25/11/2020​

In this example, both Serial A and Serial B have 2 dates occurring in the same calendar week (Serial A 24/11/20 & 25/11/20; Serial B 18/11/20 & 20/11/20). I need a way to highlight one or both rows with dates occurring in the same week for each serial number.

Any help would be greatly appreciated!!

### Excel Facts

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#### arthurbr

##### Well-known Member
Perhaps create a helper column in col C ( can be hidden) with the formula =WEEKNUM(\$B1;2) and pull down
Then use =SUMPRODUCT(--(\$A\$1:\$A\$10=\$A1),--(\$C\$1:\$C\$10=\$C1))>=2 as formula for your CF

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