Like many economic variables in a reasonably free-market economy, interest rates are determined by the forces of supply and demand. Specifically, nominal interest rates, which is the monetary return on saving, is determined by the supply and demand of money in an economy. Explain how an increase in interest rates may affect aggregate demand in an economy The first thing to do is define aggregate demand and interest rates. The interest rate is the cost of borrowing and the benefit of saving—the extra money (expressed as a percentage) to be paid back on top of a loan above the value of the loan itself, and the amount paid to savers for saving money in the bank or elsewhere. Setting interest rates involves assessing the strength of the economy, inflation, unemployment and supply, and demand. More money flowing through the economy corresponds with lower interest rates,