Final deadline to file individual tax returns 1040, etc (with extension). The deadline is Oct 15th but since it’s a weekend the due date is October 16th instead.
Final deadline to fund a SEP-IRA or solo 401(k) for tax year 2017 if you requested an automatic extension of time to file.
What if I miss the Oct 15 Deadline
If you’re getting a refund on your 2016 tax return, you have until April 15, 2020 to file the return before the statute of limitations on your refund expires. If you don’t file by then, the U.S. Treasury simply keeps your “donation.”
On the other hand, if you owe tax, that deadline has already passed.
If you still owe taxes and can’t pay it off all at once, at least try to pay off as much as you can, as soon as you can. See IRS payment options.