(1) With respect to a precomputed consumer credit sale or consumer loan, refinancing or consolidation, the parties may contract for a delinquency charge on any installment not paid in full within ten days after its scheduled due date in an amount not exceeding the greater of:

(a) Five percent of the unpaid amount of the installment, not to exceed $30; or

(b) An amount equivalent to the deferral charge that would be permitted to defer the unpaid amount of the installment for the period that it is delinquent.

(2) A delinquency charge under subdivision (a), subsection (1) of this section may be collected only once on an installment however long it remains in default. No delinquency charge may be collected with respect to a deferred installment unless the installment is not paid in full within ten days after its deferred due date. A delinquency charge may be collected at the time it accrues or at any time thereafter.

(3) No delinquency charge may be collected on an installment which is paid in full within ten days after its scheduled or deferred installment due date, even though a delinquency or deferral charge on an earlier installment may not have been paid in full.

(4) If two installments, or parts thereof, of a precomputed consumer credit sale or consumer loan are in default for ten days or more, the creditor may elect to convert such sale or loan from a precomputed sale or loan to one in which the sales finance charge or loan finance charge is based on unpaid balances. In such event, the creditor shall make a rebate pursuant to the provisions on rebate upon prepayment, refinancing or consolidation as of the maturity date of any installment then delinquent and thereafter may make a sales finance charge or loan finance charge as authorized by the appropriate provisions on sales finance charges or loan finance charges for consumer credit sales or consumer loans. The amount of the rebate may not be reduced by the amount of any permitted minimum charge. If the creditor proceeds under this subsection, any delinquency or deferral charges made with respect to installments due at or after the maturity date of the delinquent installments shall be rebated and no further delinquency or deferral charges shall be made.

(5) The commissioner shall prescribe by rule the method or procedure for the calculation of delinquency charges consistent with the other provisions of this chapter where the precomputed consumer credit sale or consumer loan is payable in unequal or irregular installments.