Oregon Revised Statutes Revenue and Taxation § 314.085

(1) The taxable year of a partnership, REMIC (real estate mortgage investment conduit), FASIT (financial asset securitization investment trust) or taxpayer shall be the same as its taxable year for federal income tax purposes.

(2) If the taxable year of a partnership, REMIC, FASIT or taxpayer is changed for federal income tax purposes, that change in taxable year shall also apply for purposes of state taxation. If a change in taxable year results in a taxable period of less than 12 months, the personal deductions and the personal exemption credits allowed by ORS chapter 316 shall be prorated under rules adopted by the Department of Revenue.

(3) Notwithstanding subsections (1) and (2) of this section, if the department terminates the taxable year of a taxpayer under ORS 314.440, the tax shall be computed for the period determined by such action.