Oregon Department of Revenue Rule Rule 150-314-0165 Filing Returns of Income: Due date Returns of income must be filed with the department on or before the fifteenth day of the fourth month following the close of the tax year. For corporations, the due date is the 15th day of the month following the due date of the federal return. Thus, when the tax year is a calendar year, the return is due on or before the fifteenth day of April in the following year. Returns received after the due date are subject to late filing penalty as provided in ORS Chapter 314 (Taxes Imposed Upon or Measured by Net Income), except that returns received by mail are accepted without the imposition of such charges if postmarked before midnight of the due date (see ORS 293.660 (Determining date of filing or receipt of reports, claims, tax returns or remittances) and 305.820 (Date when writing, remittance or electronic filing deemed received by tax officials)). When the due date falls on a Saturday, Sunday or a state legal holiday, the return is due on the next business day following such Saturday, Sunday or state legal holiday.