Currently, domestic corporations (including S corporations) must file tax their returns by the 15th day of the 3rd month after the end of their tax year. Thus, corporations following the calendar year must file their returns by March 15th of the following year.

Partnership returns are due on the 15th day of the 4th month after the end of their tax year. Therefore, partnerships using a calendar year must file their returns by April 15th of the following year.
Because the due date for a partnership return is the same as that of an individual tax return, individuals holding partnership interests must often file for an extension because their Schedule K-1’s may not arrive in time.

Now, in a major restructuring of entity return due dates under the Surface Transportation and Veterans Health Care Choice Improvement Act of 2015, partnerships and S corporations will have to file their returns (for tax years beginning after December 31st, 2015) by the 15th day of the 3rd month after the end of the tax year. Thus, entities following the calendar year must file by March 15th of the following year.

In other words, the filing deadline for partnerships will be accelerated by one month, while the filing deadline for S corporations remains the same.