Count duplicate values if they appear in the same month

Hi,

I have a spreadsheet of monthly subscriptions by customer. I am trying to identify how many customers hold multiple subscriptions for the product. I order to do this I need to count the number of times a customers email address appears in a month and if it is >1 then I would like it to return the number of duplicates.

For example:

Column A Column D
Email Address v 25/02/2021
Email Address w 02/01/2021
Email Address x 12/02/2021
Email Address y 18/02/2021
Email Address y 24/02/2021
Email Address z 10/01/2021
Email address z 10/02/2021

I would like the number 2 returned in Column J as this is the only multiple subscription in the list. The same email address appears twice in one month.

I've been going round in circles, getting close but can't quite nail it! Any help would be appreciated, thanks.

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No, I've corrected the example spreadsheet, just my poor typing!

Tow helper columns

in j6

=IF(A6=A5,J5,J5+1)

in K6

=TEXT(D6,"mmYYYY")&J6

in I6

=IF(COUNTIF($K$6:$K$1000,K6)>1,IF(COUNTIF($K$6:K6,K6)=COUNTIF($K$6:$K$1000,K6),COUNTIF($K$6:$K$1000,K6),""),""))

Thank you, I will give these a go and let you know how I get on!

Thank you these all worked, I really appreciate the responses!