Form 990, 990-EZ, or 990-PF must be filed by the 15th day of the 5th month after the end of your organization's accounting period. Thus, for a calendar year taxpayer, Form 990, 990-EZ, or 990-PF is due May 15 of the following year.
If a filing deadline falls on a Saturday, Sunday, or federal holiday, the return is considered timely filed if submitted by the following Monday. The filing deadline for tax year 2015 is May 16.