Monetary policy is the central bank changing the price of borrowing money. One small decision about an interest rate ripples out through mortgages, business loans, the exchange rate and, in the end, the whole level of demand in the economy. Follow that ripple and this topic is straightforward.
📚 What you need to know
Demand-side policies shift AD. There are two: fiscal (the government, using spending and tax) and monetary (the central bank, using interest rates and the money supply).
Central banks are usually independent and meet several times a year, so monetary policy can be changed quickly.
Expansionary (loose): cut interest rates, expand the money supply. AD shifts right.
Contractionary (tight): raise interest rates, tighten the money supply. AD shifts left.
Real interest rate = nominal interest rate − inflation rate. The real rate is what actually matters for decisions.
The transmission mechanism is the chain from the policy rate all the way through to output and inflation.
Where monetary policy sits
Both demand-side policies aim at the same thing: moving aggregate demand. They just use different levers and different people pull them.
Monetary policy serves the same macroeconomic objectives as everything else in this topic: low and stable inflation (often an explicit target such as 2%), low unemployment, steady long-term growth, smaller swings in the business cycle, and a healthy external balance. Inflation is the priority for most central banks, because the other goals are much harder to hit when prices are unstable.
Real versus nominal interest rates
“Nominal” means the number on the poster in the bank window — no adjustment for inflation. But if your savings earn 5% while prices rise 3%, you are only 2% better off in terms of what you can actually buy. That 2% is the real interest rate, and it is what households and firms respond to.
Real interest rate
real interest rate = nominal interest rate − inflation rate
WORKED EXAMPLE
Calculate the real interest rate [3 marks]
A country’s consumer price index was 108.0 in 2024 and 111.2 in 2025. The nominal interest rate in 2025 was 5%. Calculate the real interest rate in 2025.
Step 1: find inflation from the CPI change(111.2 − 108.0) ÷ 108.0 × 100= 3.2 ÷ 108.0 × 100 = 2.96%Step 2: subtract inflation from the nominal rate5% − 2.96% = 2.04%Real interest rate = 2.04%divide by the EARLIER year’s CPI — using 111.2 on the bottom is the standard slip
Why this matters. A central bank can cut the nominal rate to 1% and still be running tight policy if inflation is −1%, because the real rate is then 2%. This is exactly the problem that leads to quantitative easing.
Expansionary monetary policy
The economy is growing slowly and there is a recessionary gap. The central bank cuts rates. Loans get cheaper so firms borrow to invest, households borrow to buy cars and houses, and saving becomes less attractive so more income gets spent. Consumption and investment are both components of AD, so AD shifts right.
Reverse every arrow and you have contractionary policy: AD shifts left, real GDP falls back and the price level eases. Same diagram, opposite direction.
Contractionary monetary policy
Now the economy is booming and inflation is above target. The central bank raises rates. Existing loans and mortgages cost more to repay, so households have less to spend. Firms delay investment. Higher rates also attract money from abroad, which pushes the exchange rate up, making exports dearer and imports cheaper — so net exports fall too. AD shifts left, growth slows and inflation eases.
Rate rises → loans cost more → C and I fall → hot money flows in → currency appreciates → net exports fall → AD shifts left
The transmission mechanism
A rate change does not touch prices directly. It works through a chain, and each link takes time. This is why central banks talk about acting “ahead of” inflation rather than reacting to it.
The chain can break at any link. If households are frightened about their jobs, cheaper loans do not tempt them to borrow, and the policy stalls at step three.
In an essay, walk the chain out loud rather than jumping from “rates fall” to “inflation rises”. Every arrow you write is a potential analysis mark, and the chain is what separates a level-2 answer from a level-3 one.
What each policy does to the four objectives
Objective
Expansionary (rates cut)
Contractionary (rates raised)
Economic growth
Rises
Slows
Inflation
Rises
Eases
Unemployment
Falls, as output needs more workers
May rise, as output falls
Net external demand
Worsens — higher prices and higher incomes pull in imports
Mixed — a stronger currency hurts exports, but lower incomes cut imports
💡 Exam tips
Say which components of AD move. “Lower rates raise C and I” earns more than “AD rises”.
Label your AD/AS diagram fully: both axes, both AD curves, the AS curve, and both equilibrium points.
Use the Keynesian AS curve if the question is about an economy with a large output gap, and the classical one otherwise.
For calculations, real rate = nominal − inflation. Show the inflation working separately if you have to find it from CPI.
Remember the exchange rate route into AD. Most students only mention C and I.
Mention that central banks are independent — it is a strength worth a mark in evaluation.
⚠ Common mix-ups
Confusing monetary with fiscal. Central bank and interest rates = monetary. Government, spending and tax = fiscal.
Shifting the AS curve. Monetary policy is a demand-side policy: move AD, not AS.
Real and nominal. Nominal is the advertised rate; real subtracts inflation.
Dividing by the wrong CPI. Percentage change always divides by the earlier value.
Assuming a rate cut always works. If confidence is low, people simply do not borrow.
Forgetting the price level. Expansionary policy raises output and prices; say both.
Up next: The Central Bank’s Policy Toolkit — how banks actually create money, and the four levers a central bank pulls to change how much of it there is.
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