815 ILCS 405/7
Notwithstanding the provisions of any retail installment contract to the contrary, the buyer may prepay the contract in full, whether by payment in cash, extension, renewal or otherwise, at any time before maturity, and if he does so, shall receive a refund credit thereon for that prepayment. The amount of refund credit shall represent at least as great a proportion of the finance charge, less an acquisition cost of $25, as the sum of the periodical time balances beginning with the next payment period bears to the sum of all the periodical time balances under the schedule of installment payments in the contract. In those instances where a buyer's overpayment requires the refund credit to be given through the issuance of a negotiable instrument by the holder, no refund credit need be made if the amount of refund credit is less than $5, provided that a buyer may obtain a cash refund at the seller's or holder's location. In all other cases where the buyer's prepayment permits the refund credit to be given to the buyer as a credit on the buyer's account, no refund credit need be made if the amount of refund credit is less than $1.
815 ILCS 405/7