IL SB1641

Amends the Uniform Penalty and Interest Act to add a new subsection (b-25) applicable to returns due on or after January 1, 2024, establishing penalty rates for late tax payment of 2%, 10%, or 20% depending on payment timing and audit status.

Modifies subsection (b-20) to end its applicability on December 31, 2023, replacing it with the new (b-25) framework that includes enhanced provisions for federal change amendments required under Section 506(b) of the Illinois Income Tax Act.

Establishes that amounts resulting from federal changes reported and paid by the due date for filing the federal change amended return are deemed paid on time, eliminating penalties for those specific liabilities.

Maintains penalty reduction from 20% to 15% when entire amount due is paid within 30 days after Department provides amended return or waiver form, contingent on taxpayer not filing refund/credit claims.

Continues provisions for estimated and accelerated tax payment penalties at 2% (if paid within 30 days of due date) or 10% (if paid after 30 days).