Final deadline to file your 2016 personal tax return if you filed an extension.
October 21, 2017
Final deadline to resubmit a rejected return that was originally e-filed on or before October 16.
If you're expecting a refund and miss the October 21 final cutoff date, you have until April 15, 2020 (October 15, 2020 if you filed an extension) to file a paper return and claim your 2016 refund.