The borrower has to pay the price, i.e. interest, for getting access to the money which does not belong to him. The lender runs the risk of not being paid back the lent money. Inflation also plays spoilsport by decreasing the purchasing power of the money that the lender gets repaid in the future. Thus, the rate of interest compensates for the risks borne by the lender. In this sense, interest is income for one party and cost for another.
The rate of interest is influenced by the following factors:
Supply and Demand: The levels of interest rate affect the demand and supply of credit. Interest rate rises with an increase in demand of credit and vice versa. On the contrary, interest rate falls with an increase in supply of credit and vice versa.
Financial institutions increase the supply of credit by increasing the availability of money for loan seekers. For instance, when the income of banks increases through new customers buying various products and services, the former puts that money in lending. An increase in lending leads to a decrease in the interest rate.
The supply of credit shrinks when borrowers defer loan repayment. For instance, if a credit card holder does not make timely payments, s/he decreases the availability of money in the market. This leads to increase in the rate of interest.
Inflation: Mounting inflation leads to rise in interest rates. This is because the purchasing power of money falls during inflation. Hence, lenders try to compensate for this by charging higher interest rates.
Government: The government of a nation may also step in to regulate interest rates and to stabilize the economy.