As long as you have the creditor's name, loan amount, debtor's name and loan date (although it was added later), it meets the main requirements of the loan, so it has legal effect. Once a dispute arises, it can be used as evidence to claim creditor's rights to the people's court, and the people's court will accept it. So the IOU you said is valid.

The basic contents of IOUs include: creditor's name, loan amount (local and foreign currency), interest calculation, repayment time, liquidated damages (deferred repayment), dispute resolution method, debtor's name, loan date and other elements.

Extended data:

For legal problems, prevention is always the first, and remedy is the second. In addition to writing IOUs, we should also pay attention to the borrower, the date of borrowing, the date of repayment, the borrower's signature, the amount of borrowing, the reason for borrowing, etc. And don't make any mistakes. Besides, you should pay attention to the following five points:

1. It's best to attach the ID numbers of the lender and the borrower in the debit note to avoid unnecessary disputes.

2. When the borrower signs, the lender must see his signature with his own eyes to prevent the borrower from signing with others, and finally refuse to recognize the IOU.

3. The borrower must be the borrower, not the lender, otherwise the borrower will argue that the content is not the original.

4. Try to avoid using different languages. Simple and semantically simple IOUs are the most standard IOUs. Avoid vague language like "A borrows money from B", because it is easy to tell who is the lender and who is the borrower.

The name should be written as IOU, not IOU. Their legal meanings are quite different. IOUs are valid for 20 years and IOUs for 2 years.

Baidu encyclopedia-IOUs