# Month-end close: sales tax in Illinois Illinois's state rate is 6.25%, and the Department of Revenue sets your filing frequency from your average monthly liability. This is part of the [sales tax checklist](/month-end-close-checklist/sales-tax). Illinois sales tax is filed with the Illinois Department of Revenue (IDOR) on Form ST-1. **Rate.** 6.25% state rate (1.00% for qualifying drugs and medical appliances), plus local tax, so the rate may be higher where the client sells. **Filing.** IDOR may notify a client to file monthly if its average monthly liability is over $200, quarterly if it is $50 to $200, and annually if it is under $50. It also tells clients who must pay on an accelerated schedule. **Due.** The 20th of the month after the reporting period, or the next business day if the 20th falls on a weekend or holiday. **The trap.** Filing on time earns a discount of 1.75% of the tax due or $5 a year, whichever is greater. A payment 1 to 30 days late costs 2%, and 31 or more days costs 10%. ## The month-end steps 1. **Confirm the filing frequency.** IDOR sets it, and may change it from the average monthly liability: monthly over $200, quarterly from $50 to $200, annual under $50 [1]. Use the frequency in the client's IDOR account. Done when the frequency on file matches the account. 2. **Check the rate.** The state rate is 6.25%, and 1.00% for qualifying drugs and medical appliances. Local tax is added, so the rate may be higher [1]. Done when each taxable sale carries the state rate plus the local rate that applies. 3. **File and pay on time.** The return and any payment are due on or before the 20th of the month after the end of the reporting period. If the 20th falls on a weekend or holiday, they are due the next business day [1]. A client entitled to the discount takes 1.75% of the tax due or $5 a year, whichever is greater [1]. IDOR notifies a client that must pay on an accelerated schedule [1]. Done when each return's due date is on the client's calendar. 4. **Know what late costs.** A payment 1 to 30 days late carries a 2% penalty, and 31 or more days late carries 10% [2]. A late return carries a first-tier penalty of the lesser of $250 or 2% of the tax due on the return, reduced by timely payments or credits. If the return is still not filed 30 days after a notice of nonfiling, a second tier of the greater of $250 or 2% applies, to a maximum of $5,000, even if there is no tax due [2]. Done when each return and payment went in by its due date, or the late ones are flagged for the client. 5. **Tie the liability.** Done when the sales tax payable account is at zero after the month's payment, or equals the tax not yet due. ## Sources 1. Illinois Department of Revenue, ST-1 instructions (R-01/26), read 2026-10-24: 6.25% state rate (1.00% for qualifying drugs and medical appliances) plus local; due the 20th of the month after the reporting period, next business day on a weekend or holiday; frequency by average monthly liability (over $200 monthly, $50 to $200 quarterly, under $50 annual); accelerated payment schedule; timely-filing discount of 1.75% or $5 a year. 2. Illinois Department of Revenue, Publication 103, Penalties and interest, read 2026-10-24: late payment 2% for 1 to 30 days and 10% for 31 or more; late filing first tier the lesser of $250 or 2% of the tax, second tier the greater of $250 or 2% up to $5,000. --- Published 2026-10-24. Web page: https://www.bookkeepingforsmallbusiness.com/month-end-close-checklist/sales-tax/illinois Part of [Month-end close: sales tax by jurisdiction](https://www.bookkeepingforsmallbusiness.com/month-end-close-checklist/sales-tax).