Section 35 ILCS 735/3-2 - Interest(a) Interest paid by the Department to taxpayers and interest charged to taxpayers by the Department shall be paid at the annual rate determined by the Department. For periods prior to January 1, 2004, and after December 31, 2013, that rate shall be the underpayment rate established under Section 6621 of the Internal Revenue Code. For periods after December 31, 2003, and prior to January 1, 2014, that rate shall be: (1) for the one-year period beginning with the date of underpayment or overpayment, the short-term federal rate established under Section 6621 of the Internal Revenue Code.(2) for any period beginning the day after the one-year period described in paragraph (1) of this subsection (a), the underpayment rate established under Section 6621 of the Internal Revenue Code.(b) The interest rate shall be adjusted on a semiannual basis, on January 1 and July 1, based upon the underpayment rate or short-term federal rate going into effect on that January 1 or July 1 under Section 6621 of the Internal Revenue Code.(c) This subsection (c) is applicable to returns due on and before December 31, 2000. Interest shall be simple interest calculated on a daily basis. Interest shall accrue upon tax and penalty due. If notice and demand is made for the payment of any amount of tax due and if the amount due is paid within 30 days after the date of such notice and demand, interest under this Section on the amount so paid shall not be imposed for the period after the date of the notice and demand.(c-5) This subsection (c-5) is applicable to returns due on and after January 1, 2001. Interest shall be simple interest calculated on a daily basis. Interest shall accrue upon tax due. If notice and demand is made for the payment of any amount of tax due and if the amount due is paid within 30 days after the date of the notice and demand, interest under this Section on the amount so paid shall not be imposed for the period after the date of the notice and demand.(d) No interest shall be paid upon any overpayment of tax if the overpayment is refunded or a credit approved within 90 days after the last date prescribed for filing the original return, or within 90 days of the receipt of the processable return, or within 90 days after the date of overpayment, whichever date is latest, as determined without regard to processing time by the Comptroller or without regard to the date on which the credit is applied to the taxpayer's account. In order for an original return to be processable for purposes of this Section, it must be in the form prescribed or approved by the Department, signed by the person authorized by law, and contain all information, schedules, and support documents necessary to determine the tax due and to make allocations of tax as prescribed by law. For the purposes of computing interest, a return shall be deemed to be processable unless the Department notifies the taxpayer that the return is not processable within 90 days after the receipt of the return; however, interest shall not accumulate for the period following this date of notice. Interest on amounts refunded or credited pursuant to the filing of an amended return or claim for refund shall be determined from the due date of the original return or the date of overpayment, whichever is later, to the date of payment by the Department without regard to processing time by the Comptroller or the date of credit by the Department or without regard to the date on which the credit is applied to the taxpayer's account. If a claim for refund relates to an overpayment attributable to a net loss carryback as provided by Section 207 of the Illinois Income Tax Act, the date of overpayment shall be the last day of the taxable year in which the loss was incurred.(e) Interest on erroneous refunds. Any portion of the tax imposed by an Act to which this Act is applicable or any interest or penalty which has been erroneously refunded and which is recoverable by the Department shall bear interest from the date of payment of the refund. However, no interest will be charged if the erroneous refund is for an amount less than $500 and is due to a mistake of the Department.(f) If a taxpayer has a tax liability for the taxable period ending after June 30, 1983 and prior to July 1, 2002 that is eligible for amnesty under the Tax Delinquency Amnesty Act and the taxpayer fails to satisfy the tax liability during the amnesty period provided for in that Act for that taxable period, then the interest charged by the Department under this Section shall be imposed at a rate that is 200% of the rate that would otherwise be imposed under this Section.(g) If a taxpayer has a tax liability for the taxable period ending after June 30, 2002 and prior to July 1, 2009 that is eligible for amnesty under the Tax Delinquency Amnesty Act, except for any tax liability reported pursuant to Section 506(b) of the Illinois Income Tax Act (35 ILCS 5/506(b)) that is not final, and the taxpayer fails to satisfy the tax liability during the amnesty period provided for in that Act for that taxable period, then the interest charged by the Department under this Section shall be imposed in an amount that is 200% of the amount that would otherwise be imposed under this Section.(h) No interest shall be paid to a taxpayer on any refund allowed under the Tax Delinquency Amnesty Act. Amended by P.A. 098-0425,§ 15, eff. 8/16/2013.Amended by P.A. 096-1435,§ 20, eff. 8/16/2010.Amended by P.A. 095-0331,§ 420, eff. 8/21/2007.Amended by P.A. 093-0032, § 50-40, eff. 6/20/2003.Amended by P.A. 093-0026, § 905, eff. 6/20/2003.P.A. 89-379, eff. 1-1-96; 91-803, eff. 1-1-01.