If it was sold in 2016, it goes on the 2016 tax return. If the loss offsets all other income on the 2016 tax return, you probably have a Net Operating Loss (NOL) that can be carried to an amended 2014 tax return (if it is not used up in 2015, the excess is carried to 2015, then 2017).

When you said it was sold at a $300,000 loss, does that include the depreciation that lowered the Basis? If it was originally a personal-use property and was later converted to a rental property, did you account for the possible Dual Basis rules (if that applies and you are unsure of what I mean, please post back)?