California Code, Civil Code - CIV § 1810.12

(a) Notwithstanding Section 1810.4, a seller or holder of a retail installment account may, subject to subdivision (d) of Section 1810.3, provide that for each installment in default the buyer shall pay a delinquency charge not in excess of one of the following amounts:

(b) Only one delinquency charge may be collected on any installment regardless of the period during which it remains in default.  No delinquency charge shall be imposed for any default of payment on any payment due prior to the mailing or delivery to the buyer of the written disclosure concerning the delinquency charge provided by the seller or holder of a retail installment account pursuant to subdivision (d) of Section 1810.3.  Payments timely received by the seller under a written extension or deferral agreement shall not be subject to any delinquency charge.  The agreement may also provide for payment of any actual and reasonable costs of collection occasioned by removal of the goods from the state without written permission of the holder, or by the failure of the buyer to notify the holder of any change of residence, or by the failure of the buyer to communicate with the holder for a period of 45 days after any default in making payments due under the agreement.

(c) Notwithstanding subdivision (b) of Section 1810.3, the seller or holder of a retail installment account shall provide a minimum of 20 days between the monthly billing date and the date upon which the minimum payment is due, exclusive of the applicable grace period provided in subdivision (a).