Control by the central bank

Monetary policy is a demand-management policy through which a central bank changes the money supply or interest rates to influence aggregate demand and macroeconomic outcomes. This is demand-side intervention. Its immediate aim is to change total spending, rather than the economy's productive capacity.

A central bank is a public monetary authority responsible for managing monetary conditions in an economy. Its role depends on the monetary system: it may directly influence the money supply, set an official policy interest rate, or use both approaches. Commercial banks pass these changes on to households and firms through the rates they offer on savings and loans.

The interest rate is the percentage cost of borrowing or reward for saving over a period of time. When interest rates change, they affect borrowing, saving, consumption and investment. As a result, aggregate demand, real output, employment and the average price level may also change. The key here is the transmission mechanism, not simply the announcement of a new rate.

Price stability and inflation targeting

A central goal is price stability: a low and reasonably predictable inflation rate, rather than a price level that never changes. When inflation is stable, people and firms can plan more easily. Money remains useful, and arbitrary changes in real income and wealth are reduced.

Inflation targeting is a monetary-policy framework in which a central bank publicly commits to keeping inflation at or near a stated rate or within a stated range. When forecast inflation remains above the target, the bank may tighten policy. If inflation is below target while demand is weak, it may loosen policy instead. Central banks usually take a forward-looking approach because changes in interest rates affect the economy after a delay.

Employment, stability and growth

Monetary policy can pursue several connected goals:

• Low unemployment: when spare capacity exists, stronger aggregate demand can increase firms' sales and output, raising their demand for labour.
• Reduced business-cycle fluctuations: lower interest rates can moderate recessions, while higher rates can restrain excessive demand during booms.
• A stable environment for long-term growth: predictable inflation and financial conditions reduce uncertainty, which supports investment. Monetary policy cannot create sustained increases in productive capacity by itself, but greater stability can make this growth easier.
• External balance: changes in interest rates can influence capital flows and the exchange rate, affecting export and import expenditure. Shifts in domestic demand also change spending on imports.

These goals may conflict. Tighter policy can reduce inflation, but it may also weaken growth and increase cyclical unemployment. Looser policy may support employment in the short run, yet generate inflation or external pressure if demand grows faster than productive capacity. Monetary policy therefore requires choices; it cannot achieve every objective simultaneously without cost.

Lending and deposit creation

A commercial bank is a financial institution that accepts deposits and provides loans to households and firms. A reserve is an asset held by a commercial bank as vault cash or as a balance at the central bank rather than being lent to customers. Banks keep reserves so they can meet withdrawals and payment obligations.

When a bank grants a loan, it usually credits the borrower’s deposit account. That new deposit is available to spend, so the act of lending creates deposit money. After the money is spent, it may arrive at another bank. This bank keeps part as reserves and lends the rest. As lending and redepositing continue, deposits can expand by a multiple across the banking system.

A minimum reserve requirement is a regulation requiring commercial banks to keep a specified proportion of eligible deposits as reserves. In the simplified IB model, lowering the required proportion gives banks more to lend. Raising it restricts lending.

The maximum simple deposit multiplier is

$$m = \frac{1}{rr}$$

where $m$ is the maximum deposit multiplier (dimensionless) and $rr$ is the required reserve ratio (dimensionless, expressed as a decimal).

For example, if $rr=0.10$, the simple multiplier is 10. Under the model’s assumptions, a new reserve injection of 2,000 currency units could support up to 20,000 currency units of total deposits. The first bank keeps 200 and lends 1,800. Once that money is redeposited, the next bank keeps 180 and lends 1,620. The process then continues with progressively smaller amounts.

Why the result is a maximum

The model assumes that banks lend every unit of excess reserves and borrowers spend every loan. It also assumes that all funds return to the banking system and banks hold no excess reserves. In practice, cash withdrawals, weak demand for loans, cautious bank behaviour or regulatory constraints reduce the amount created. The formula gives a theoretical ceiling, not a promise that deposits must rise by that amount.

Changing liquidity and lending conditions

Central banks have several tools for loosening or tightening monetary conditions. The chain of causation matters here. First, the tool changes bank reserves, lending conditions or the money supply. Market interest rates and credit then adjust, followed by spending.

Open market operations are central-bank purchases or sales of government securities in financial markets to alter bank reserves and the money supply. When the central bank buys securities, it credits the banking system with reserves. This supports more lending and lower interest rates. Selling securities does the reverse: it withdraws reserves, restricts lending and puts upward pressure on rates.

A change in the minimum reserve requirement affects the proportion of deposits banks must retain. Lowering the requirement increases potential lending and money creation; raising it reduces both. The instrument can be powerful because many banks are affected at the same time.

The central bank minimum lending rate is the interest rate charged by the central bank when it lends reserves to commercial banks. It may also be known as the base, discount or refinancing rate. If the rate falls, central-bank funding becomes cheaper and banks are generally encouraged to lend at lower rates. If it rises, banks face higher funding costs and credit conditions generally tighten.

Quantitative easing is a policy under which a central bank creates reserves to purchase financial assets, usually on a large scale, to lower longer-term borrowing costs and increase liquidity. This tool is especially relevant when the short-term policy rate is already very low. Asset purchases increase demand for bonds, pushing up their prices and lowering their yields. They also add reserves to the banking system. Quantitative tightening removes this support through asset sales or by allowing assets to mature without replacing them.

The expansionary and contractionary directions of the four tools can be compared side by side.

How major monetary-policy tools operate in expansionary and contractionary directions.

The money market

Money is an asset that is generally accepted as a means of payment. In this model, money covers currency and readily accessible bank deposits used for transactions.

Demand for money is the quantity of money balances that households and firms are willing and able to hold at each interest rate. Holding money instead of an interest-bearing financial asset has an opportunity cost, represented by the interest rate. When the interest rate rises, the opportunity cost rises too, so the quantity of money demanded falls. This gives the money-demand curve its downward slope.

Supply of money is the quantity of money balances available in the economy at a particular time. The simplified diagram shows it as a vertical curve fixed by the central bank. Along this curve, money supply does not change with the interest rate.

The equilibrium interest rate is the interest rate at which the quantity of money demanded equals the quantity supplied. This is where the money-demand and money-supply curves intersect. If money supply shifts right, there is excess supply at the old rate and the equilibrium interest rate falls. A leftward shift creates excess demand, causing the equilibrium interest rate to rise.

In a correct diagram, the interest rate goes on the vertical axis and the quantity of money on the horizontal axis. Draw a downward-sloping money-demand curve and a vertical money-supply curve, then label the intersection. In this model, do not show money supply as an ordinary upward-sloping market-supply curve.

Distinguishing the two rates

A nominal interest rate is the stated percentage return to saving or cost of borrowing before adjustment for inflation. By contrast, a real interest rate is the nominal interest rate adjusted for the change in the purchasing power of money caused by inflation. The real rate matters to savers and borrowers because it shows how the purchasing power of their funds changes.

For the IB calculation, use the approximation

When rates expressed in percent are subtracted, the answer is in percentage points per year.

Suppose the nominal interest rate is 6% and inflation is 2.5%. The real interest rate is 3.5%. If the nominal rate is 2% while inflation is 4%, the real rate is -2%. The nominal return is positive, but the purchasing power of the saved funds is falling.

Use the language carefully. A fall in inflation doesn’t necessarily mean deflation. Likewise, a lower real interest rate doesn’t necessarily show that the nominal rate has fallen; inflation may simply have risen.

Expansionary policy and a recessionary gap

Aggregate demand is the total planned expenditure on domestically produced final goods and services at each average price level in a given period. It consists of consumption and investment, together with government spending and net exports.

Expansionary monetary policy is a demand-side policy that lowers interest rates or increases the money supply to raise aggregate demand. Cheaper borrowing encourages interest-sensitive consumption and investment. At the same time, a lower reward for saving may lead people to spend now. Lower interest rates can also trigger capital outflows and currency depreciation, which increase net exports, although other conditions affect the size of this exchange-rate effect.

An economy has a recessionary gap when equilibrium real output is below potential output. Stronger aggregate demand shifts the aggregate-demand curve to the right, raising real output and the average price level while reducing cyclical unemployment. The shift must be the right size to close the gap.

Where the economy starts makes a difference. If there is substantial spare capacity, expansion is likely to raise real output by more and the price level by less. Near potential output, inflation is likely to account for more of the effect.

Contractionary policy and an inflationary gap

Contractionary monetary policy is a demand-side policy that raises interest rates or reduces the money supply to lower aggregate demand. More expensive borrowing discourages credit-financed consumption and leaves fewer investment projects profitable. A higher reward for saving may also delay consumption, while currency appreciation may reduce net exports.

An inflationary gap exists when equilibrium real output exceeds potential output. Lower aggregate demand shifts the aggregate-demand curve to the left. Demand-pull inflationary pressure falls and output moves back towards its sustainable level, though short-run growth also declines and cyclical unemployment may rise.

Write the full transmission chain as an argument rather than making a jump: the policy instrument changes; interest rates or credit conditions respond; components of aggregate demand adjust; aggregate demand shifts; and equilibrium output and the average price level change.

Strengths

Monetary policy is incremental. A central bank can shift its policy stance in relatively small steps, assess new evidence and then make another adjustment. This lowers the risk of introducing one unnecessarily large change.

Monetary policy is also flexible and easily reversible. A monetary-policy committee can change interest rates without rewriting the government budget. If inflation or employment develops unexpectedly, or financial conditions change, the committee can reverse course. Decision and implementation lags are therefore often shorter than those associated with fiscal policy. However, the full transmission from an official rate change to spending, output and inflation may still take considerable time.

These characteristics can make contractionary monetary policy effective against demand-pull inflation. Higher interest rates discourage borrowing and spending. A credible inflation target may also stop expectations of continuing inflation from becoming embedded. The Bank of England, for example, raised its policy rate repeatedly from late 2021 as inflation intensified. Household and business credit conditions tightened, although falling energy prices and easing supply disruption also helped inflation decline later.

Constraints

There is limited scope to reduce nominal interest rates when they are close to zero. Further small cuts may be impractical, while banks may remain unwilling to lend and customers unwilling to borrow. Asset purchases can add stimulus, but their effect on ordinary spending is uncertain.

Weak consumer and business confidence can disrupt the transmission mechanism. In a severe downturn, households may choose to save instead of spending. Firms might reject even cheap loans if they expect poor sales, while commercial banks may become more cautious about lending. Monetary policy is often considered more reliable at restraining excessive demand than at forcing pessimistic private agents to spend.

Japan's long experience with very low interest rates shows this constraint. Inexpensive credit did not consistently generate strong demand because consumption and investment were also shaped by weak expectations, demographic change and other structural forces. An interest-rate change must therefore be linked to its economic context rather than assumed to work automatically.

Judging performance against the objectives

For growth and low unemployment, expansionary policy works best when deficient aggregate demand is the main problem, banks are prepared to lend and spare capacity exists. Its impact is weaker if unemployment is structural or if shortages of labour, energy or capital constrain production. Monetary policy influences spending; it cannot directly retrain workers or increase productive capacity.

For low and stable inflation, contractionary policy can tackle demand-pull inflation effectively, but it is less capable of resolving cost-push inflation. After an imported energy shock, higher rates may suppress second-round demand and inflation expectations. They cannot create additional energy. A sharper trade-off between inflation, output and employment is therefore likely.

For external balance, the outcome depends on exchange-rate responsiveness, global interest rates and what caused the imbalance. Higher interest rates may attract financial inflows and cause the currency to appreciate. This can weaken net exports, even as lower demand reduces imports, so the channels may operate in opposing directions.

Factors determining the effectiveness of monetary policy

Interdependence and an overall judgement

Policy effectiveness depends on interdependence. Economic conditions, including spare capacity and debt, shape sensitivity to interest rates. Political arrangements influence central-bank credibility, while social conditions affect how costs are shared between borrowers and savers, or homeowners and renters. Environmental shocks may also cause inflation that demand management cannot directly remove. For instance, a rate rise could improve price stability but worsen equity and short-run economic well-being for heavily indebted households.

Scarcity forces policymakers to choose between competing objectives. Intervention may improve stability and allocative efficiency by reducing damaging inflation. Yet excessive tightening can come at the cost of employment and investment, including investment required for sustainable long-term growth. Any judgement should therefore depend on the cause of the problem and the economy's initial position, alongside confidence, bank behaviour, time lags, debt exposure, and the size and timing of the policy change.