You have a list of contracts and due dates for annual maintenance fees. You wish to determine when you have a contract coming due in the next 45 days and provide a note that warns you that the payment is coming due.
One way of providing a note could be with a formula like this on the place where you want the note to appear:
=IF(TODAY()+45>A1,"Warning: Payment is coming due","")
Change the reference from A1 to the cell with the due date.
You can format the cell as you want, to make sure that the note is visible.