if you did not file a valid extension by now you have incurred a (5% a month for a maximum of 5 months) 25% IRS penalty for late filing (failure-to--file-penalty) + interest this is in addition to the late payment penalties and interest, so it behooves you that pay ASAP. States also have late filing and payment penalties. these penalties are generally figured on the balance due. Technically, the IRS late payment penalty of .5% a month doesn't start until the after the late-filing period ends
