Highlight duplicate dates who share unique ID

[Andrewjs]

Hey I've been all over Google with this and have got close but i can't seem to get the right syntax for Excel to execute how i want.

Ultimately i will be using conditional formatting and will convert the [HEADER] names to A2 / B2 format etc but i've been trying to first get the logic right as a formula in a column.

Column A has ID numbers, mostly unique but there are some duplicates, which i identify easily with COUNTIF

Column B has dates, many rows may share the same date so i'm not interested in knowing how many total duplicates of dates there are...


What i'm after is identifying how many duplicate dates in column B there are WHILE column A is a known duplicate. (If column A has duplicates, column B of those particular rows need unique dates, COUNT not to exceed 1)

I've tried other variations of COUNTIF and SUMPRODUCT but this is the latest thing i've tried. Is not quite right:

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Small example of what i'd like it to show:

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Anybody shed some light?
Thanks!

[63falcondude]

A simple COUNTIFS should do

C2 =COUNTIFS(A:A,A2,B:B,B2)

[Andrewjs]

Bingo!! Working great, nice and simple. Thanks a lot.

[63falcondude]

You're welcome. Thanks for the rep!

If you need a hand implementing the Conditional Formatting, let us know.