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. Aggregate demand is the total demand for goods and services in an economy at a given time, and we can express aggregate demand using the national income identity, where AD = C + I + G + EX - IM, i.e., consumption plus investment plus government spending plus exports minus imports. Using this identity, and thinking about how more expensive borrowing and more attractive saving will impact consumer and firm behaviour, we can answer the question.

If interest rates increase, it becomes more expensive to borrow money (since there is a larger amount to be paid back on top of the value of the loan) and more beneficial to save money (since banks will pay more for saving). This means that consumers are less likely to take out loans and more likely to store their money in the bank, leading to a reduction in consumption—less consumer spending, more saving. Likewise with firms, which will be less likely to invest in new capital (because borrowing funds to buy it costs more) and more likely to save profits. This reduction in consumption and investment means that aggregate demand falls, represented in a diagram by a shift to the left.

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Depending on the level of the student/how far they are along with A-Level or IB etc., we could also talk about the effects of interest rates on the exchange rate via capital flight and how this will impact exports and imports, as well as potential government bond prices and how this could impact fiscal spending or at least the government's finances.