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quarters, he shall file a return with the Department each month by the 20th day of the month next following the month during which such tax liability is incurred and shall make payments to the Department on or before the 7th, 15th, 22nd and last day of the month during which such liability is incurred. On and after October 1, 2000, if the taxpayer's average monthly tax liability to the Department under this Act, the Use Tax Act, the Service Occupation Tax Act, and the Service Use Tax Act, excluding any liability for prepaid sales tax to be remitted in accordance with Section 2d of this Act, was $20,000 or more during the preceding 4 complete calendar quarters, he shall file a return with the Department each month by the 20th day of the month next following the month during which such tax liability is incurred and shall make payment to the Department on or before the 7th, 15th, 22nd and last day of the month during which such liability is incurred. If the month during which such tax liability is incurred began prior to January 1, 1985, each payment shall be in an amount equal to 1/4 of the taxpayer's actual liability for the month or an amount set by the Department not to exceed 1/4 of the average monthly liability of the taxpayer to the Department for the preceding 4 complete calendar quarters (excluding the month of highest liability and the month of lowest liability in such 4 quarter period). If the month during which such tax liability is incurred begins on or after January 1, 1985 and prior to January 1, 1987, each payment shall be in an amount SB3019 Enrolled LRB104 20255 HLH 33706 b Public Act 104-0468