Hi esthela_v:
It is unclear from your question if you are the "forgiver" of the debt, or if you were the beneficiary of a "forgiven" debt. Therefore, we'll handle this question from both perspectives.
First, if you are holder of a debt instrument or obligation, and you either determine that it is uncollectable from the borrower, or that you simply decide to forgive for other reasons, then that "tax event" occurs at the time period the decision not to attempt further collection activity is made. Therefore, if a lender reaches this decision sometime in 2016, then that is the applicable period for reporting the debt as a "loss" for income tax accounting purposes.
Second, if you are instead in the position of the borrower, then what matters to you is when you receive a Form 1099-C (Cancellation of Debt) income from a lender. You would report that debt income, then, in the tax year during which you received the actual form. (If you get or got a Form 1099-A, instead of a Form 1099-C, then you can ignore the 1099-A until you later receive the 1099-C.)
Essentially, then, as a borrower it doesn't matter to you when the debt was forgiven, per se, but when you received the 1099-C. That is the tax year in which you would report your cancellation of debt income.
If you received a Form 1099-C in 2015, but did not report it on your 2015 tax return, then it would be improper to do so on your 2016 return. In that case you should "Amend" your 2015 tax return. But, if you receive a Form 1099-C in 2016, for a 2015 debt, then you would report it on your 2016 tax return, not 2015. Does that logic make some sense?
Finally, here are some links to additional information we have on both Amending a 2015 tax return in TurboTax, as well as Form 1099-C and debt forgiveness.
https://ttlc.intuit.com/questions/3410543
and
https://ttlc.intuit.com/questions/1901111-what-is-form-1099-c
Thank you for asking about this important topic.
