A deferment charge may be charged and collected on a loan made under Section 18636 if the payment date of all wholly unpaid installments on which no default charge has been collected is deferred one or more full months and the loan contract so provides. Such deferment charge shall not exceed the portion of precomputed charge applicable, prior to deferment, to the first deferred monthly installment period multiplied by the number of months the maturity of the contract is deferred. Such number of months shall not exceed the number of full installments which are in default on the date of deferment or which may become due within 15 days of such date. When a deferment charge is
made, no portion of the precomputed charge shall apply to the installment periods in which no installment payment is required by reason of the deferment. In computing any default charge or required rebate, the portion of the precomputed charge applicable to each deferred balance and installment period following the deferment period and prior to the deferred maturity shall remain the same as that applicable to such balances and periods under the original contract of loan. Such charge may be collected at the time of deferment or at any time thereafter. Any payment received at the time of deferment may be applied first to the deferment charge and the remainder, if any, applied to the unpaid balance of the loan contract; provided, however, if such payment is sufficient to pay, in addition to the appropriate deferment charge, any installment which is in default and the applicable default charge, it shall be first so applied and any such installment shall not be deferred nor subject to the deferment
charge.