Legal analysis: the validity of IOUs is permanent, but the limitation of action is three years. If, during this period, you have evidence to prove that you asked the other party to pay back the money or the other party returned some money to you, the limitation of action will be interrupted and recalculated from the date when you asked him to pay back the money or the other party returned some money to you.

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

Article 667 A loan contract is a contract in which the borrower borrows money from the lender, repays the loan at maturity and pays interest.

Article 668 A loan contract shall be in written form, unless otherwise agreed between natural persons.

The contents of a loan contract generally include terms such as loan type, currency, purpose, amount, interest rate, term and repayment method.

Article 669 When concluding a loan contract, the borrower shall, at the request of the lender, provide the true information about the business activities and financial status related to the loan.