Extensions do not actually need to be paid at the time of filing. However, Brett Sloan is correct in that you must make either estimated tax payments based upon what is owed and/or the projected income and taxes for the next year. Making payment arrangements at the time of filing gives you a figure to work with.  You may decide upon making arrangements with the IRS that paying up front instead of extending with the late payment penalty worth filing and paying now. For those waiting for forms, file now, save the penalties and fees and file a 1040X to include the late form later.