That's for the 1098 mortgage interest. If the property was rented the entire year, then it's 100%.
Take note that vacant periods between renters counts for days rented too, provided you did not live in the property for one single day during that vacancy "for personal pleasure use" of any kind.
It's not uncommon for a rental property owner to live in the property for a week or so between tenants for the purpose of getting things ready for the next tenant. Especially if the owner lives to far away to be commuting every day. Those are not personal use days.
