There is no penalty for filing a form 1040 after the deadline so long as you are due a refund. Penalties and interest only accrue on unfiled returns if the taxes were not paid by April 18. Anybody who does expect to owe taxes should file and pay as soon as they can to keep the penalty amounts as low as possible.
The late-filing penalty for unpaid taxes is usually 5 percent for each month or part of a month your tax return is late. If you file more than 60 days late, the minimum penalty is either $210 or 100 percent of the unpaid tax, whichever is less.
So get those tax returns filed, and if you think you are going to owe – like you do every year – you can always go online at https://www.irs.gov and make apply a payment toward your 2017 form 1040.