Interest refers to the amount generated by deposits or loans in a certain period of time. Principal refers to the amount initially deposited or lent. Interest rate refers to the percentage of interest to principal, usually expressed in the form of annual interest rate. If you want to calculate the interest amount in a specific time, interest = principal × interest rate × time. Time is usually in years, and if it is in other units (such as months or days), it needs to be converted into corresponding proportions. For example, on a monthly basis, you need to divide the annual interest rate by 12 to get the monthly interest rate.