Cambridge International AS and A Level Economics: Monetary policy and supply-side policy (9708)

This guide covers sections 5.3 (Monetary policy) and 5.4 (Supply-side policy) of the Cambridge International AS & A Level Economics 9708 syllabus for examination in 2026, 2027 and 2028. Topic 5 is AS Level content. A Level candidates study it too, and the syllabus treats AS content as assumed knowledge for A Level Papers 3 and 4. Every country, firm and figure below is invented for illustration. None is a real statistic, and money is in currency units (cu).

Start from the Cambridge A Level Economics hub or the printable checklist. After this guide, use the revision notes and the practice questions. The AD and AS guide explains the curves used here, and a free 10-minute diagnostic shows where you stand.

What this guide covers

Outcome	What you must be able to do
5.3.1	Define monetary policy
5.3.2	Explain the tools: interest rates, money supply and credit regulations
5.3.3	Distinguish expansionary from contractionary monetary policy
5.3.4	Use AD/AS to show how monetary policy changes equilibrium national income, output, prices and employment
5.4.1	Explain supply-side policy in terms of its effect on LRAS curves
5.4.2	State the objectives: higher productivity and productive capacity
5.4.3	Explain tools such as training, infrastructure development and support for technological improvement
5.4.4	Use AD/AS to show how supply-side policy changes equilibrium national income, output, prices and employment

Monetary policy works mainly on the demand side (AD). Supply-side policy works on the supply side (AS). Keep that contrast in mind throughout.

5.3.1 What monetary policy is

Monetary policy means the government or its central bank adjusting interest rates, the money supply or credit regulations to influence the level of aggregate demand and so meet objectives such as price stability, low unemployment and economic growth. Which body takes the decisions differs between countries, so write “the government or central bank” unless the question names one.

5.3.2 The tools

Interest rates

The central bank sets a policy (base) interest rate. Commercial banks move their own lending and saving rates in the same direction. A change affects AD through several routes:

• Borrowers: a lower rate cuts the cost of loans and variable-rate mortgages, so households keep more income to spend.
• Savers: a lower rate reduces the reward for saving, so saving falls and consumption rises.
• Firms: a lower rate makes more investment projects worth undertaking.
• Confidence and asset values: cheaper borrowing tends to raise demand for housing and other assets.

Worked example 1 (cost of borrowing). The policy rate in Country M falls from 5% to 3.5%. A small bakery has an interest-only loan of 200,000 cu.

• Interest at 5%: 200,000 x 0.05 = 10,000 cu a year.
• Interest at 3.5%: 200,000 x 0.035 = 7,000 cu a year.
• Saving: 3,000 cu, a 30% fall in the interest bill.

A household with a 150,000 cu variable-rate mortgage sees the rate fall from 6% to 4.5%. Annual interest falls from 9,000 cu to 6,750 cu, a saving of 2,250 cu a year, or 187.50 cu a month. That extra disposable income can be spent.

Worked example 2 (investment). A firm considers a 500,000 cu machine that is expected to add 27,500 cu a year to profit before interest. That is a return of 27,500 / 500,000 = 5.5%.

• Borrowing at 4.5% costs 22,500 cu a year, leaving a gain of 5,000 cu. The firm invests.
• Borrowing at 6% costs 30,000 cu a year, leaving a loss of 2,500 cu. The firm does not invest.

A fall in interest rates therefore raises investment, which is a component of AD.

Nominal and real rates. The real interest rate is approximately the nominal rate minus the inflation rate. If the nominal rate is 4% and inflation is 1.5%, the real rate is about 2.5%. If inflation rises to 3.5% with the nominal rate unchanged, the real rate is about 0.5%. Real rates matter for saving and borrowing decisions.

Money supply

The money supply is the total money in the economy. The central bank can add to it, for example by buying government bonds from banks, which increases the reserves that banks can lend. In a money market diagram, the vertical axis is the interest rate and the horizontal axis is the quantity of money. The demand for money slopes downward because holding money costs the interest forgone. The money supply is a vertical line set by the central bank.

Interest rate (%)	Demand for money (cu bn)
6	300
5	340
4	380
3	420
2	460

If the money supply is 380 cu bn, the equilibrium rate is 4%. If the central bank raises the money supply to 420 cu bn, the equilibrium rate falls to 3%. If it cuts the supply to 340 cu bn, the rate rises to 5%. Money supply and interest rates are linked: a central bank that controls the money supply influences the price of borrowing.

Credit regulations

These are rules on how much banks may lend and on what terms. An example is a cap on the loan-to-value ratio for mortgages. For a house costing 250,000 cu:

• Cap of 80%: the largest loan is 200,000 cu, so the buyer needs a deposit of at least 50,000 cu.
• Cap of 70%: the largest loan is 175,000 cu, so the deposit is at least 75,000 cu, which is 50% more.

Fewer buyers can afford the larger deposit, so borrowing and spending fall even if interest rates do not change. Looser credit rules do the opposite.

5.3.3 Expansionary and contractionary policy

	Expansionary	Contractionary
Interest rates	Cut	Raised
Money supply	Increased	Reduced
Credit rules	Relaxed	Tightened
Effect on AD	Shifts right	Shifts left
Typical use	Weak growth, high unemployment	Inflation above target, overheating

5.3.4 AD/AS analysis

Axes: price level (vertical) and real output (horizontal). Expansionary policy shifts AD to the right. The new equilibrium is at a higher real output and a higher price level. Contractionary policy shifts AD left, giving lower real output and a lower price level (or slower price rises in a growing economy).

Worked example 3 (expansionary policy). Country M is in a downturn. In a model, AD is Y = 1,100 - 4P and short-run AS (SRAS) is Y = 400 + 6P, where Y is real output in cu bn and P is the price index.

• Equilibrium: 1,100 - 4P = 400 + 6P, so 10P = 700 and P = 70. Y = 1,100 - 280 = 820.
• Lower rates raise AD by 80 at every price: Y = 1,180 - 4P. Then 10P = 780, so P = 78 and Y = 868.
• Real output rises by 48, which is 5.9%. The price level rises by 8, which is 11.4%.
• If each 100 cu bn of extra output employs about 1 million more people (an invented rule), employment rises by about 480,000.
• The gap to full-capacity output (taken as 1,000) shrinks from 180 to 132.

Worked example 4 (contractionary policy). Country N is overheating. AD is Y = 1,360 - 4P and SRAS is Y = 400 + 6P.

• Equilibrium: 10P = 960, so P = 96 and Y = 976.
• Higher rates and tighter credit cut AD by 60: Y = 1,300 - 4P. Then P = 90 and Y = 940.
• The price level is 6.25% lower than it would have been and real output falls 3.7%. With the same employment rule, about 360,000 jobs are lost.

The trade-off is clear: reducing inflationary pressure costs output and jobs.

Evaluating monetary policy

• Time lags: firms and households respond slowly, and many fixed-rate loans do not change at once.
• Confidence: in a deep downturn, lower rates may not persuade firms to invest or banks to lend.
• Spare capacity: expansion raises output if there is spare capacity. Near full capacity it mainly raises prices.
• Cause of inflation: raising rates is better suited to demand-pull inflation than cost-push inflation, where it also reduces output.
• Winners and losers: lower rates help borrowers and hurt savers.

5.4 Supply-side policy

5.4.1 Meaning and the LRAS curve

Supply-side policy aims to raise the economy’s capacity to produce by improving the quantity or quality of factors of production or their efficiency. In AD/AS terms it shifts the long-run aggregate supply (LRAS) curve to the right. If LRAS is drawn as a vertical line at full-capacity output, the line moves from, say, 1,000 to 1,060 cu bn, a 6% increase in capacity. If LRAS is drawn in three sections, the rightward shift moves the vertical section. Lower unit costs can also shift SRAS right.

5.4.2 Objectives

• Increase productivity: output per worker or per unit of input.
• Increase productive capacity: the maximum the economy can produce, an outward shift of the production possibility curve.

These support economic growth, lower costs and prices, and more jobs without the inflationary pressure that comes with a pure demand boost.

5.4.3 Tools

Training and education. Worked example 5: Country S has 25 million workers producing 1,000 cu bn, so productivity is 1,000 bn / 25 m = 40,000 cu per worker. A programme trains 4 million workers (16% of the workforce) and raises their output by 10%.

• Trained workers: 4 m x 44,000 = 176 bn. Others: 21 m x 40,000 = 840 bn.
• New output: 1,016 bn, up 1.6%. Output per worker rises from 40,000 to 40,640 cu.
• At 2,000 cu per trainee the cost is 8 bn a year against a gain of 16 bn a year, if the gain is repeated.

Infrastructure development. Suppose a delivery takes 40 minutes, of which 25 are travel. A new road cuts travel to 15 minutes, so a delivery takes 30 minutes. In a 480-minute day a driver makes 16 deliveries instead of 12, an increase of 33.3%.

Support for technological improvement. If a firm spends 500,000 cu on research and the government pays 30%, the government bears 150,000 cu and the firm 350,000 cu. A lower cost to the firm encourages more research.

The syllabus lists these as examples. Other measures, such as better health care, tax incentives for investment or reducing barriers to starting a business, are also valid if they improve productivity or capacity.

5.4.4 AD/AS analysis

Start from Country S: AD is Y = 1,200 - 4P and SRAS is Y = 400 + 6P, so P = 80 and Y = 880.

• The policy lowers costs and shifts SRAS right by 60: Y = 460 + 6P. Then P = 74 and Y = 904.
• Real output rises 2.7%, the price level falls 7.5%, and about 240,000 jobs are added (using the same invented employment rule).
• LRAS moves right, so capacity rises and the economy can sustain more output in future.

Unlike expansionary monetary policy, output rises while the price level falls.

Evaluating supply-side policy

• Long time lags: training and infrastructure take years to pay off.
• Cost: the opportunity cost of government spending can be large.
• Uncertain effect: workers may not use new skills, or firms may not use new technology.
• Complements AD policy: more capacity gives no benefit if demand is too weak to use it.

Common errors

• Shifting AD for a supply-side policy, or LRAS for a monetary one.
• Saying a lower interest rate makes saving more attractive.
• Forgetting the price level rises under expansionary policy near full capacity.
• Treating a movement along SRAS as a shift.
• Giving only a list of tools with no chain of reasoning to AD or AS.

Official syllabus

Cambridge International AS & A Level Economics 9708, syllabus for examination in 2026, 2027 and 2028, version 2, published by Cambridge University Press & Assessment. This guide covers sections 5.3 and 5.4.