Start counting your "personal use days" after the rental was placed in service in September. The idea is that you are dividing the home's expenses between rental use and personal use for the period of time during which the home was used as a Rental (Sept. through Dec.) and only the expenses that pertain to the Rental will be deducted on the Schedule E.
You may take the full deduction for mortgage interest and property taxes applicable from June through August and the personal use apportioned amount from September through December of on Schedule A, if you itemize your deductions.
Please comment if you need additional help with this.
