Count Days down to a due date

Brianne

If I have a "Due Date" column, and I want another column to calculate the amount of days leading up to that date… what formula would be created? It would be marked "Closed" if completed and "Open" if not completed.

Additionally when that item is passed the "due date" and still "Open" we would like to count the amount of days overdue in a negative number. What would we use here?