Start with the adjusted basis in the property you sold, which includes any original mortgage you took out.
Add the value of any other property you transfer in the exchange, the mortgage amount on your new property, the amount of cash you’re contributing to the new purchase, and any recognized gain on the sold property. (Note: Not all of these will apply to every 1031 exchange.)
Subtract any money or property you received in the exchange, the amount of the mortgage on the sold property, and any recognized loss on any property sold in the exchange.
