It is illegal if the annual loan interest rate exceeds four times the one-year floating interest rate. The one-year loan interest rate is 4.5, so the interest of 3,600 per year exceeds the regulations and is illegal. If the lender requests the borrower to pay interest according to the interest rate agreed in the contract, the People's Court shall support the request, except where the interest rate agreed upon by both parties exceeds four times the one-year loan market quotation rate at the time the contract is established. Legal basis: Article 680 of the "People's Republic of China and Civil Code" prohibits usury lending, and the interest rate for borrowing must not violate relevant national regulations. If the loan contract does not stipulate the payment of interest, it will be deemed that there is no interest. If the loan contract does not clearly stipulate the payment of interest, and the parties cannot reach a supplementary agreement, the interest will be determined according to local or party transaction methods, transaction habits, market interest rates and other factors; if the loan is borrowed between natural persons, it will be deemed to have no interest.