California
Civil Code – CIV § 1916-1
The rate of interest upon the loan or forbearance of any money, goods or things in action or on accounts after demand or judgments rendered in any court of this state, shall be seven dollars upon the one hundred dollars for one year and at that rate for a greater or less sum or for a longer or a shorter time; but it shall be competent for parties to contract for the payment and receipt of a rate of interest not exceeding twelve dollars on the one hundred dollars for one year and not exceeding that rate for a greater or less sum or for a longer or shorter time, in which case such rate exceeding seven dollars on one hundred dollars shall be clearly expressed in writing.