Is the mortgage on a rental property a write off ? or just the interest, repairs and insurance type stuff??

No, your losses from principal mortgage payments cannot be used in that manner on a residential rental property.

Your mortgage payments cannot be used as an expense  on a residential rental property.

You can not deduct the mortgage payment;You can  deduct  the mortgage interest. You can, and should, deduct depreciation [land is not depreciated] .  If you don't the IRS will treat it as if you did.  That will have very  serious negative consequences when you sell the property.You will also have other expenses that you can claim, insurance, taxes and repairs.

Please complete the rental section (Schedule E) so that you will be able to claim all related expenses and depreciation [land is not depreciated] , so if any passive loss , that can be carried forth  even  up to the time the property is sold.However, unused losses do carry forward and can be applied to future years.  If you sell the property, any unused losses can be used to increase the basis of the property at sale.  So, you do get the losses, but they are deferred.

If you expenses exceed your rental income, you have a loss.  If the rental income exceeds your expenses, you have a profit.

Where do I enter income and expenses from a rental property?

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