(1) If, upon receipt of an application by a taxpayer for a refund, or upon examination of the returns or records of any taxpayer, the department determines that within the statutory period for assessment of taxes, penalties, or interest prescribed by RCW
83.100.095 a person required to file the Washington return under RCW
83.100.050 has overpaid the tax due under this chapter, the department shall refund the amount of the overpayment, together with interest as provided in subsection (2) of this section. If the application for refund, with supporting documents, is filed within one hundred twenty days after an adjustment or final determination of federal tax liability, the department shall pay interest until the date the refund is mailed. If the application for refund, with supporting documents, is filed after one hundred twenty days after the adjustment or final determination, the department shall pay interest only until the end of the one hundred twenty-day period.
(2) Interest refunded under this section for periods before January 2, 1997, shall be computed at the rate provided in RCW
83.100.070(1). Interest refunded under this section for periods after January 1, 1997, through December 31, 1998, shall be computed on a daily basis at the rate as computed under RCW
82.32.050(2) less one percentage point. Interest allowed for periods after December 31, 1998, shall be computed at the rate as computed under RCW
82.32.050(2). Except as provided in subsection (1) of this section, interest shall be refunded from the date of overpayment until the date the refund is mailed. The rate so computed shall be adjusted on the first day of January of each year.
(3) Except as otherwise provided in subsection (4) of this section and RCW
83.100.090, no refund shall be made for taxes, penalties, or interest paid more than four years prior to the beginning of the calendar year in which the refund application is made or an examination of records is complete.
(4) The execution of a written waiver under RCW
83.100.095 shall extend the time for making a refund if, prior to the expiration of the waiver period, an application for refund is made by the taxpayer or the department discovers a refund is due.
(5) An application for refund shall be on a form prescribed by the department and shall contain any information and supporting documents the department requires.