Legal analysis: there is an iou, which belongs to the civil legal relationship, that is, the creditor-debtor relationship, so it is not illegal. Moreover, for private loans, the maximum interest rate shall not exceed 4 times the interest rate of similar loans of banks (including interest rates). Beyond this limit, the excess interest will not be protected.

Legal basis: Article 680 of the Civil Code of People's Republic of China (PRC) prohibits high-interest lending, and the lending rate shall not violate the relevant provisions of the state.