Conditonal Formating

I have a training spread sheet that is used to track the due date of the training for our field personnel. We also use it to determine if the training will expire prior to a field operation. So when I put in a Field operation date in cell A3 I want to compare it to the training due date in cell H7, if H7 is before A3 I want it to fill orange. I tried cell value < A3 but it gives very strange results. The DateDif function doesn't work when you have a large selection of data. Any ideas.