1. Bank loans are usually calculated at the annual interest rate.

2. Suppose the annual interest rate is x%(x is a percentage), and the annual repayment of principal plus interest is: 20000 * (1+x%).

Because the loan has to be paid off within two years, half of the total amount has to be paid off every year: (20000 * (1+x%))/2.

4. To get the specific repayment amount, you need to know the actual annual interest rate.

Summary:

To determine how much you need to pay back a year, you need to know the annual interest rate of the loan. According to the loan amount and annual interest rate, the amount that should be paid off every year can be calculated. Please note that this answer is only a rough estimate, and the actual repayment amount may be affected by other factors.

Extended data:

The loan interest rate is determined by the bank according to the market situation and personal credit evaluation. Interest rates directly affect the cost and repayment amount of loans. Before applying for a loan, it is recommended to consult a bank or lending institution to obtain accurate interest rate information and understand relevant loan conditions and repayment plans.