August 1, 2016, is the deadline for filing retirement or employee benefit returns (5500 series) for plans on a calendar year. (The usual due date of July 31, 2016, is a Sunday.)
You'll also want to note two IRS updates regarding Form 5500. First, the compliance questions are optional. Form 5500 includes new compliance questions for 2015 tax years (returns with a due date of August 1, 2016, for calendar year filers). Because the questions were not approved by the Office of Management and Budget, the instructions for Form 5500 say plan sponsors should skip them when completing the form.
Also, some Form 5500-EZ filers will need to file electronically. If you're required to file at least 250 returns of any type with the IRS, including information returns (for example, Form W-2 and Form 1099), you may need to electronically file Form 5500-EZ for calendar year 2015.