It depends.

If you paid back taxes for the 2014 and 2015 tax year in 2016, you can list the full amount paid under the real estate tax section (combined with the 2016 property taxes) under rental expenses.

However, if you paid these 2014 and 2015 property taxes in 2014 and 2015 respectively, you will need to amend your 2014 and 2015 tax returns to include these property taxes on your Schedule E for those prior years.

 Click How to Amend a Return You Already Filed for more information about amending a prior year return