Legal analysis: An iou with a written date is invalid. Pay attention when writing IOUs: (1) Write the name accurately; (2) clearly stipulate interest; (3) provide guarantee; If the loan amount is huge, the borrower shall be required to provide a guarantee to ensure the safety of the loan funds.

Legal basis: Civil Code of People's Republic of China (PRC).

Article 675 The borrower shall repay the loan within the agreed time limit. There is no agreement or unclear agreement on the loan period.

Article 510 If it is still uncertain, the borrower may return it at any time; The lender may urge the borrower to return it within a reasonable period of time.