OAR 150-314-0325: Estimated Tax: Computation of Underpayment

(1) Underpayment charges shall be assessed on the last filed return received before the due date for such return. That return shall be considered the “original return,” and the tax due shall be used as the basis for computing the underpayment charges. (2) Once underpayment charges are assessed on the original return, an amended return, reducing the tax liability, shall not reduce the underpayment charges.