In database design, the devil is in the details. How have you set up your database? What tables and relationships? Are you using a starter solution or a modified copy of a starter solution?
Much depends on your current system for getting an inventory count of what is in and what is out. A transactions table that logs each date that an item is checked out and each time that it is returned can probably be used with future dates in the date field to get the predictive capability that you want here.