If you have been using TurboTax over the period of the rentals, TurboTax normally calculates this and automatically insert on the form.
If not you will need to refer to each tax return and review Form 4562 (Depreciation Schedule) Part II Line 14 for each year the property was rented to determine the amount.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"