Agencies
Services
How is interest calculated and what is the current interest rate?
Interest charged to you: Interest begins to accrue the day after the date the payment is due through the date you pay the tax.
Interest paid by the state of Illinois: Unless an overpayment is refunded or a credit is approved within 90 days after the return due date, interest will be paid to you from the due date of the original return, the date a processable return is filed, or the date of overpayment (whichever date is latest).
Rate: For interest accruing on or after January 1, 2014, the rate of interest payable on overpayments and underpayments is the "underpayment rate". This rate is established by the IRS under the IRC Section 6621. Please visit our Interest Rates webpage for a list of the current rates.