California Code, Health and Safety Code - HSC § 127458

The emergency physician shall reimburse the patient or patients any amount actually paid in excess of the amount due under this article, including interest. Interest owed by the emergency physician to the patient shall accrue at the rate set forth in Section 685.010 of the Code of Civil Procedure, beginning on the date payment by the patient is received by the emergency physician. However, an emergency physician is not required to reimburse the patient or pay interest if the amount due is less than five dollars ($5). The emergency physician shall give the patient a credit for the amount due for at least 60 days from the date the amount is due.