Section 205 ILCS 205/6004 - Calculation of interest; postpayments and prepayments(a) In any contract or loan that is secured by a mortgage, deed of trust, or conveyance in the nature of a mortgage for the purpose of purchase or refinance of residential real estate, the interest that is computed, calculated, charged, or collected pursuant to the contract or loan, or pursuant to any regulation or rule promulgated under this Act, may not be computed, calculated, charged or collected for any period of time occurring after the date on which the total indebtedness, with the exception of late payment penalties, is paid in full.(b) For purposes of this Section, a prepayment means the payment of the total indebtedness, with the exception of late payment penalties if incurred or charged, on any date before the date specified in the contract or loan agreement on which the total indebtedness shall be paid in full, or before the date on which all payments, if timely made, shall have been made. In the event of a prepayment of the indebtedness that is made on a date after the date on which interest on the indebtedness was last computed, calculated, charged, or collected but before the next date on which interest on the indebtedness was to be calculated, computed, charged, or collected, the lender may calculate, charge, and collect interest on the indebtedness for the period that elapsed between the date on which the prepayment is made and the date on which interest on the indebtedness was last computed, calculated, charged, or collected at a rate equal to 1/360 of the annual rate for each day which so elapsed, which rate shall be applied to the indebtedness outstanding as of the date of prepayment. The lender shall refund to the borrower any interest charged or collected that exceeds that which the lender may charge or collect under this subsection.