March 15 Deadline - Partnerships and S Corps
The deadline for filing calendar year 2018 partnerships and S corporations is March 15, 2018. These returns must be filed (e-filed or postmarked) by midnight (local time) on March 15, 2018. Fiscal year returns will be due the 15th day of the 3rd month following the year-end.
Both partnership and S corporation returns are allowed a six-month extension if needed. Payment must accompany the return or extension if there are taxes due. An extension of time to file does not extend the time to pay taxes that are due.

April 17 Deadline - Individuals, C Corps, Estates, and Trusts
The deadline for filing calendar year individual, C corporation, estate, and trust returns is April 17, 2018. Calendar year C corporations are now eligible for an automatic six-month extension.