Can't file by the tax deadline?
If you're planning to get a refund, there’s no need to panic if you do not file by April 18, 2017 (this year's tax deadline). Taxpayers receiving a refund will not have to pay a penalty if they do not file by April 18. However, you should still file as soon as possible.
If you plan to owe additional tax, you need to submit by April 18 an extension to file (Form 4868) with the amount you will owe to avoid penalty. If you don't know how much you will owe, last year's tax return is a good indicator. Submit that amount in payment. It's important to note that an extension to file is not an extension to pay.