A simple interest calculator uses three basic inputs: principal amount, rate of interest, and time. Based on these, it shows the interest earned and the total value at the end of the period.
The bank discount rate is a calculation of the interest investors earn on short-term instruments such as Treasury bills.
Interest can be charged when you borrow money or earned when you save. When you charge something on a credit card or take out a loan from a financial institution (student loan, auto loan, mortgage, ...