Calendar year partnership, S corporation, C corporation, estate and trust returns that are on extension are due Monday, September 15, 2014. Except in extremely rare circumstances (e.g. natural disaster), no further extensions are available. Even if your entity cannot pay, file timely!
The penalties for late filing are harsher than the late payment penalties. Late filing penalties are in addition to late payment penalties so filing late compounds an already bad situation for those who cannot pay by the due date.