Taking a loss on rental property for taxes?

sounds like you may actually have some income there. You can only offset rental income with valid expenses. A mortgage payment is not a valid expense. The mortgage interest is, and then only that portion attributable to the rental activity, which in this case would probably be only 50% of what you pay in interest. Seek a tax pro for istance with this, cuz you probably have other expenses, like depreciation, insurance, etc.