Michigan Compiled Laws, Chapter 445. Trade and Commerce § 445.873

(a) The number and amount of installment payments required to be stated under section 3  1 may be estimated for purposes of this section assuming that each scheduled payment is made on the date it is due and in the scheduled amount.

(b) The holder of the contract has the option of deferring interest charges that accrue due to installment payments being received later than the periodic installment due date. The deferred interest charge shall be computed on the basis of additional interest charges accruing for late installment payments and appropriate interest reductions for installment payments made before the due date. On contracts providing for equal monthly installments, if the final installment is more than 105% of a previous installment as a result of the deferred interest charges, the installment buyer shall be given the option to pay the deferred interest charges not less than 25 days after the date the last installment payment is due.

(c) If the entire principal balance is prepaid in full, together with all interest incurred to the date of prepayment, the balance of the original time price differential shall be canceled and the provisions of section 8  2 respecting a refund credit shall not be applicable.