A valid extension of time in which to file your federal return automatically extends the due date of your Oklahoma return if no Oklahoma liability is owed. A copy of the federal extension must be provided with your Oklahoma return. If your federal return is not extended or an Oklahoma liability is owed, an extension of time to file your Oklahoma return can be granted on Form 504-I.
90% of the tax liability must be paid by the original due date of the return to avoid penalty charges for late payment. Interest will be charged from the original due date of the return.