Here is a photo of an example

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Basically what i want to do:

I wanna have an expiry date on invoices. The expiry date to be 7 days from the day it was created.

In the expiry date coloumn, i want it to automatically know its out of date and then use conditional formatting to show it highlited red.

So basically if the invoice was created on the 10/08/2010, i want it to expire on the 17th. So i would put it in the expiry dat coloum "17/08/2010". If i check it everyday, it will be normal, but on the 17th (7 days after), i want it that it is red (conditional formatting or something). If there a code for that?

Also, saying this, i want it to relate to peaople that have paid or pending. I want it to say, "if coloum paid = Y, then leave normal, if column paid = Pending and then date of over 7 days of expiry then show me that its red"

Does anyone know a formula for me or can do one for me fromthe picture i showed you?