Tax returns—Filing.

(1)(a) Except as otherwise provided in this section or RCW 82.32.080, taxpayers owing tax under this chapter must file, on forms prescribed by the department, a return with the department on or before the date the taxpayer's federal income tax return for the taxable year is required to be filed. Individuals not owing tax under this chapter are not required to file a return under this section.(b)(i) Except as provided in (b)(ii) of this subsection (1), returns and all supporting documents must be filed electronically using the department's online tax filing service or other method of electronic reporting as the department may authorize.(ii) The department may waive the electronic filing requirement in this subsection for good cause as provided in RCW 82.32.080.(2)(a) Every taxpayer owing tax under this chapter must include with the Washington return described in subsection (1) of this section a copy of the taxpayer's federal income tax return filed with the internal revenue service of the United States, including:(i) All federal income tax forms, schedules, and other attachments that directly relate to the taxpayer's federal adjusted gross income; and(ii) Any information returns and federal tax documents received by the taxpayer that directly relate to the taxpayer's federal adjusted gross income including, but not limited to, form W-2, form 1099-INT, form 1099-DIV, form 1099-NEC, form 1099-MISC, form 1099-B, schedule K-1 (form 1065), and schedule K-1 (form 1120-S).(b) A taxpayer must provide to the department, upon request, other federal tax return information needed to verify the tax owed under this chapter.(c) The department may prescribe by rule additional reporting or verification requirements under this subsection (2) to substantiate an individual's federal adjusted gross income.(d) The department may prescribe by rule additional Washington-specific reporting or verification requirements under this subsection (2), such as a Washington schedule K-1 form, to substantiate an individual's Washington base income.(3) Each taxpayer required to file a return under this section must, without assessment, notice, or demand, pay any tax due thereon to the department on or before the date fixed for the filing of the return, regardless of any filing extension. The tax must be paid by electronic funds transfer as defined in RCW 82.32.085 or by other forms of electronic payment as may be authorized by the department. The department may waive the electronic payment requirement for good cause as provided in RCW 82.32.080. If any tax due under this chapter is not paid by the due date, interest and penalties as provided in chapter 82.32 RCW apply to the deficiency.(4) If a taxpayer has obtained an extension of time for filing the federal income tax return for the taxable year, the taxpayer is entitled to the same extension of time for filing the return required under this section. An extension under this subsection for the filing of a return under this chapter is not an extension of time to pay the tax due under this chapter.(5)(a) If any return due under subsection (1) of this section, along with a copy of the federal income tax return, is not filed with the department by the due date or any extension granted by the department, the department must assess a penalty in the amount of five percent of the unpaid tax due, as of the due date for the return, for the taxable year covered by the return for each full month that the return remains unfiled. The total penalty assessed under this subsection may not exceed 25 percent of the unpaid tax due, as of the due date for the return, for the taxable year covered by the delinquent return. The penalty under this subsection is in addition to any penalties assessed for the late payment of any tax due on the return.(b) The department must waive or cancel the penalty imposed under this subsection if:(i) The department is persuaded that the taxpayer's failure to file the return by the due date was due to circumstances beyond the taxpayer's control; or(ii) The taxpayer has not been delinquent in filing any return due under this section during the preceding five calendar years and the taxpayer has not been contacted by the department for enforcement purposes regarding the reporting period covered by the waiver request.(6) The department must waive or cancel the penalty imposed under RCW 82.32.090(1) on a payment required under this section when the circumstances under which the delinquency occurred do not qualify for waiver or cancellation under RCW 82.32.105(1) if all of the following apply:(a) A taxpayer requests a waiver of penalty for a payment required under this section;(b) The taxpayer has not been contacted by the department for enforcement purposes regarding the reporting period covered by the waiver request; and(c) The taxpayer has timely remitted payment on all tax returns due under this section during the preceding five calendar years.(7)(a) In the event a taxpayer's federal income tax return is changed in a manner that is final after their return required under subsection (1) of this section is filed with the department and the taxpayer's federal income tax return is changed in a manner that impacts either the calculation of their Washington adjusted gross income or their tax liability under this chapter, or both, the taxpayer must amend the taxpayer's return due under subsection (1) of this section for the same tax year in which their federal income tax return is changed. For the purposes of this subsection (7), a federal income tax return is changed in a manner that is final when such change is not subject to either administrative review by the United States internal revenue service or judicial review in a court of competent jurisdiction, or both. A change is also final in the case of an audit finding in the following circumstances:(i) The taxpayer has received audit findings from the internal revenue service for the tax period and the taxpayer does not timely file an administrative appeal with the internal revenue service.(ii) The taxpayer consented to any of the audit findings for the tax period through a form or other written agreement with the United States internal revenue service.(b) If the return is not amended, as required under this subsection (7), with the department within 90 days of the federal income tax return change becoming final, the department must assess on the 91st day a penalty in the amount of five percent of any additional tax due for the taxable year covered by the return for each month or portion of a month that the return is not timely amended as required by this subsection. The total penalty assessed under this subsection (7)(b) may not exceed 25 percent of the additional tax due for the taxable year covered by the delinquent return amendment. The penalty under this subsection (7)(b) is in addition to any penalties assessed under this section.(8)(a) No assessment or correction of an assessment for additional taxes, penalties, or interest due may be made by the department more than four years after the year in which a return is filed under subsection (1) of this section except:(i) When the taxpayer's federal income tax return is changed in a manner that requires an amended return under subsection (7) of this section; or(ii) As provided in RCW 82.32.050(4).(b) In the event the statute of limitations is extended under (a)(i) of this subsection, no assessment or correction of an assessment for additional taxes, penalties, or interest due may be made by the department more than four years after the year in which an amended return is filed with the department as required under subsection (7) of this section. Any assessment or correction of an assessment for additional taxes, penalties, or interest due under this subsection (8)(b) but made by the department more than four years after the year in which a return is filed under subsection (1) of this section must be directly related to the federal income tax return change described in subsection (7) of this section.(9) If the federal government extends the due date for filing a tax return, paying tax, or both, by reason of natural disaster or other occurrence, the corresponding deadlines under this section shall be adjusted in the same manner.[ 2026 c 238 s 702.]Notes:Findings—Intent—Effect of invalidation of 2026 c 238 s 201—Automatic expiration date and tax preference performance statement exemption—Necessity of act—Intent—Implementation by department of revenue—2026 c 238: See notes following RCW 82A.04.030.