Legal analysis: IOU can be regarded as a loan contract, and it has legal effect when both parties sign it voluntarily. In order to protect the interests of lenders more comprehensively and prevent legal risks, lenders can write all the more detailed loan information clearly. Such as repayment time, repayment method and other related information.

Legal basis: Article 409 of the Civil Code of People's Republic of China (PRC). If the parties sign a contract in the form of a contract, the contract is established when both parties sign or seal it.