Guide

Behind on Illinois sales tax: how costs grow and where to start

Falling behind on sales tax happens to careful people. The cost grows with time, so the best moment to deal with it is now.

General information only, not legal or tax advice. I am not a CPA or an attorney.

Why it gets expensive

• Penalties. Late filing and late payment each carry penalties. A commonly cited schedule has a late-payment penalty of 2% for payments up to 30 days late and 10% after that, and a late-filing penalty of the lesser of $250 or 2% of the tax. Confirm the current amounts in IDOR Publication 103.
• Interest. Interest runs on the unpaid tax from the day after the due date. IDOR sets the rate and updates it twice a year.
• Lost discount. Filing or paying late can cost you the vendor's discount, which is 1.75% of the tax, or $5 a year if greater, up to $1,000 a month.
• More periods pile up. Each month or quarter you skip adds another return and another round of penalties.

The money may not be yours to spend

Sales tax you collected from customers is held in trust for the state. If it was spent, the situation is more serious than a simple late fee. The law can make responsible people personally liable, including owners of an LLC. Read why compliance matters, then talk to a CPA or an attorney before you decide what to do.

Where to start

1. Do not ignore notices. Open mail and messages from the Illinois Department of Revenue. Deadlines in them matter.
2. Gather your records. Sales reports by month, payment processor exports, and any returns you already filed. If you sell through marketplaces, note which orders the marketplace already taxed.
3. List the periods. Which months or quarters were not filed, and which were filed but not paid?
4. Talk to a CPA or an attorney before filing back returns, especially if several periods are missing or you collected tax and did not send it in. They can tell you what options exist.
5. Ask IDOR about your options. Ask whether a payment arrangement is available and how to file past-due returns in MyTax Illinois.
6. Set up a system so it does not repeat. A calendar reminder for the 20th, and a separate account for tax you collect.

What not to do

• Do not stop collecting or filing and hope it goes away.
• Do not file a return with numbers you know are wrong.
• Do not pay a stranger who promises to make the debt disappear.

How I can help

I can help you get your records organized and understand the filing process, but I do not give tax or legal advice and I do not represent you before IDOR. For decisions about back returns, penalties or payment plans, that is a CPA's or attorney's job.

I am not a CPA or an attorney

This page is general information, not legal or tax advice. Rules, fees and forms change, so confirm with the agency. For advice about your situation, talk to a CPA or an attorney.

Sources: Illinois penalty and discount summary (secondary); 35 ILCS 735/3-7; Illinois Department of Revenue. Checked Oct 27, 2026.