Yes, since the return must be
postmarked by Tuesday, April 18, 2017. So, if you have it post marked by Tuesday, April 18, 2017 or before, you met the deadline.
For additional information please review the following.
Tax Year 2016 Calendar: Important Dates and Deadlines
https://ttlc.intuit.com/replies/3302298
If
you're a calendar year filer and your tax year ends on December 31, the
due date for filing your federal individual income tax return is
generally April 15 of each year. If you use a fiscal year (tax year
ending on the last day of any month other than December), your return is
due on or before the 15th day of the fourth month after the close of
your fiscal year. If your due date falls on a Saturday, Sunday, or legal
holiday, the due date is delayed until the next business day. For
example, April 15, 2017 is on a Saturday; Emancipation Day in the
District of Columbia is Sunday, April 16, 2017, and is observed on
Monday, April 17, 2017. So even if you don't live in the District of
Columbia, tax year 2016 returns are due Tuesday, April 18, 2017. Your return is considered filed on time if the envelope is properly addressed, postmarked, and deposited in the mail by the due date.
https://www.irs.gov/taxtopics/tc301.html
