Your formula in conditional formatting could be (where D2 is cell with the
date):
=IF(DATEDIF(TODAY()+1,D2,"m")<3,TRUE,FALSE)

This method, as opposed to adding 90 days will highlight anything that is
within 3 calendar months. If run today is Nov 25, it will highlight every
date from Nov 26 to Feb 25. The 90 day method will highlight up to Feb 23.



"HR gal" wrote:

I am working with a spreadsheet having to do with various training my staff
must have. Some of the certificates expire after a few years, and I wanted
to enter a function so that a cell is highlighted when it is within 3 months
from expiring, so that I will know to schedule a new training session. I
tried using the Conditional Formatting option, but wasn't sure what formula
to write. Help!