A committee of about nine people meets eight times a year and changes one number. That number is not a tax, not a budget, and not a law, yet it moves mortgage payments, business investment, the exchange rate and eventually the price of almost everything. Monetary policy is the most powerful lever in macroeconomics operated by people nobody elected, and understanding why it is arranged that way is half of understanding the topic.
Monetary policy
The use of interest rates, the money supply and sometimes the exchange rate by a central bank to influence the level of economic activity and achieve macroeconomic aims.
Money supply
The total amount of money in an economy at a given time, including notes and coins and money held in bank accounts.
The commonest lost mark here is attributing monetary policy to the government. It is conducted by the central bank, and in most countries the central bank is operationally independent of the government precisely so that it is not. Fiscal policy is the government's; monetary policy is the central bank's. Getting that wrong in the first line undermines everything after it.
The instruments
There are three instruments and the syllabus expects all of them. The interest rate is the main one: the central bank sets a policy rate, and commercial banks move their own lending and saving rates with it. The money supply can be changed directly, by buying or selling government bonds, which puts money into or takes it out of the banking system. And the exchange rate can be influenced, since buying or selling the domestic currency changes its value and therefore the price of imports and exports. In practice the interest rate does most of the work, but an answer naming only one instrument has answered a third of the question.
At AS a fourth tool is added: credit regulation. The central bank, or the government, can limit how much banks lend directly, rather than through the price of borrowing. It can require banks to hold more reserves or capital against their loans, set limits on how much can be lent relative to a house's value or a borrower's income, or restrict lending to particular sectors. Tighter credit regulation reduces lending and spending even if interest rates are unchanged, and it can be targeted at one part of the economy, such as an overheating housing market, which the interest rate cannot.
Expansionary monetary policy means cutting the interest rate or increasing the money supply. Borrowing becomes cheaper, saving less rewarding, and total demand rises. It is used when growth is weak and unemployment is rising. Contractionary monetary policy means raising the interest rate or reducing the money supply, which dampens borrowing and spending. It is used when inflation is climbing. The direction follows the problem, exactly as with fiscal policy.
A change in the interest rate reaches ordinary households through several routes at once. Mortgage and loan repayments rise or fall, which changes how much income is left to spend. Saving becomes more or less attractive, which changes how much is set aside rather than spent. Borrowing to buy cars, furniture and other durable goods becomes cheaper or dearer. Firms feel it too: a project that was worth borrowing for at 3% may not be at 6%, so investment plans are shelved. Households with large mortgages and firms that borrow heavily feel it most, which is one reason the effects are uneven.
Explain questions on interest rates are marked on the linking, not on the list. 'Interest rates rise so demand falls' is one mark at best. 'Interest rates rise, so mortgage repayments increase, so households have less disposable income, so consumption falls, so aggregate demand falls' is the same idea earning four times as much. Name each step.
Nominal and real interest rates
Real interest rate = nominal interest rate - rate of inflationThis is the approximation, and it is the one Cambridge expects. The exact relationship is (1 + nominal) / (1 + inflation) - 1, which matters only at high inflation rates. Formulae are not printed in any 9708 paper, so recall it.
Working out whether a saver is actually gaining
A bank pays savers a nominal interest rate of 3.5% a year. Inflation over the same year is 5.1%. Calculate the real interest rate and explain what it means for the saver.
Which of the following is an instrument of monetary policy?
A central bank raises interest rates. Other things being equal, the most likely effect on the exchange rate is:
Draw a demand and supply diagram for loanable funds, or for money, showing the interest rate on the vertical axis. Show the effect of the central bank increasing the money supply, and mark the new equilibrium interest rate.
The point of the diagram is that the central bank cannot set the interest rate and the money supply independently. Increasing the supply of money pushes the equilibrium interest rate down; targeting a lower interest rate requires supplying more money. Choosing one determines the other, which is a distinction examiners reward at AS and above.
The transmission mechanism
At AS the effect has to be traced through aggregate demand rather than asserted. A policy rate is not itself a component of AD. It works by changing consumption and investment, and by moving the exchange rate and therefore net exports. The route from a rate decision to a change in output runs through several markets and takes months, which is why the chain below matters more than the headline.
How a rate rise reduces demand-pull inflation
- The central bank raises its policy rate in response to inflation above target.
- Commercial banks raise lending and deposit rates, since their own cost of funds has risen.
- Borrowing becomes more expensive and saving more rewarding, so households postpone consumption, particularly of durables bought on credit.
- Firms face a higher cost of capital, so marginal investment projects no longer clear their required rate of return and investment falls.
- Higher domestic rates attract financial inflows, demand for the currency rises and it appreciates.
- Appreciation makes exports dearer abroad and imports cheaper at home, so net exports fall.
- Consumption, investment and net exports have all fallen, so aggregate demand shifts left.
- The price level rises more slowly, so the inflation rate falls, at the cost of lower output and higher unemployment in the short run.
AO2 analysis is 40% of the written papers. Note that three separate AD components move here, and the exchange rate channel is the one candidates most often omit. Including it is a cheap way to lift an answer.
Practise this chain →Draw an AD/AS diagram for an economy experiencing demand-pull inflation with AS steepening near full capacity. Show the effect of contractionary monetary policy on AD, the price level and real output. Then draw the same shift on an economy in deep recession where AS is flat.
Drawing both is the point. Near capacity the leftward AD shift lands mostly on the price level, which is the policy working as intended. In deep recession the same shift costs a great deal of output for very little price effect. The state of the economy determines whether the policy is well judged, and saying so explicitly is worth marks.
Most central banks now operate an inflation target, commonly around 2%, set by the government but pursued independently. The target is symmetric: undershooting is a failure too, because deflation brings its own problems as households delay purchases expecting lower prices later. Independence exists because a government facing an election has a short-run incentive to cut rates and let inflation follow, and everyone knowing that in advance makes inflation harder to control. Handing the decision to a body with a single published objective makes the commitment credible, and credibility is itself a policy instrument, because expectations of future inflation feed into today's wage and price setting.
Why does an independent central bank with a published inflation target tend to achieve lower inflation than a government setting rates directly?
Applied context
The tightening cycle that began in 2022 is the clearest recent illustration. Major central banks raised policy rates rapidly from near zero after inflation rose well above target, having spent the previous decade unable to push inflation up to it. Two features are worth carrying into an answer. Mortgage holders on variable or expiring fixed rates absorbed the impact far more sharply than outright owners or those on long fixes, so the burden fell very unevenly across households. And the lag was long enough that rates were still rising while some of the earlier increases had not yet fully fed through, which is precisely the difficulty the theory predicts.
Use this to support a specific point about incidence or about lags, not as scene setting. One example used precisely beats several mentioned in passing.