California Code, Financial Code - FIN § 22307

(a) Except as provided in Section 22305 and Article 4 (commencing with Section 22400), all charges on loans made under this division shall be computed and paid only as a percentage per month of the unpaid principal balance or portions thereof, and shall be so expressed in every obligation signed by the borrower. The charges on loans shall be computed on the basis of the number of days actually elapsed. For the purpose of these computations, a month is any period of 30 consecutive days.

(b) The loan contract shall provide for payment of the aggregate amount contracted to be paid in substantially equal periodical installments, the first of which shall be due not less than 15 days nor more than one month and 15 days from the date the loan is made. This subdivision shall not apply to a loan made to a graduate student at an accredited college or university while the student is actively pursuing a study program leading to a postbaccalaureate degree, or to a student loan made by an eligible lender under the Higher Education Act of 1965, as amended (20 U.S.C. Sec. 1070 et seq.), or to a student loan made pursuant to the Public Health Service Act, as amended (42 U.S.C. Sec. 294 et seq.).

(c) This section shall not apply to open-end loans.