I have to manually calculate these figures too often.  It is very common here for someone to own a home with an attached "ohana" (aka mother daughter studio), and have a cottage on the same property, and be using a portion of the main home for business with all of the mortgage, property taxes, etc., paid together.  We need a way to be able to separate the mortgage interest & property taxes between the 8829s (sometimes more than one home office for different businesses), E, and A.  Just carrying from E to A or 8829 to A is insufficient and means we have to manually calculate on a spreadsheet and manually enter the figures on all forms.