Almost every macroeconomics question in the exam eventually becomes the same question: something happened, so which way does AD move and why? Once you can route any piece of news through one of the four components, you can answer all of them. This page is that routing map.
📘 What you need to know
A change in any non-price determinant of AD shifts the entire curve.
An increase in any component shifts AD right, so real GDP is higher at every price level.
A decrease shifts AD left, so real GDP is lower at every price level.
Consumption responds to confidence, interest rates, wealth, income tax, household debt and expectations of future prices.
Investment responds to interest rates, business confidence, technology, business taxes and corporate debt.
Government spending responds to political and economic priorities.
Net exports respond to trading partners’ incomes, exchange rates and trade policy.
What a shift looks like
Read the diagram horizontally. Pick any price level, hold it still, and see how much real GDP is demanded on each curve. That is what a shift actually means.
At the price level AP1, the economy demands Y1 on the original curve, Y2 after an increase in AD, and only Y3 after a decrease. The price level never changed. What changed is how much the economy wants to buy at that price level.
What moves consumption
Determinant
How it works
Effect on AD
Consumer confidence
When people feel secure in their jobs and expect steady pay, they spend more and save less. In a downturn the reverse happens and precautionary saving rises.
Confidence up: shifts right
Interest rates
Higher rates reward saving, and raise the monthly cost of mortgages and loans, leaving less money for everything else.
Rates up: shifts left
Wealth
Rising house or share prices make households feel richer and more willing to borrow against that wealth, even if their income has not changed.
Wealth up: shifts right
Income tax
Disposable income is what is left after tax and after benefits received. Lower income tax means more disposable income to spend.
Tax up: shifts left
Household debt
Debt is repaid monthly. The more of household income that goes on repayments, the less is left for new spending.
Debt up: shifts left
Expected future prices
If people expect prices to rise, they bring purchases forward to beat the increase. If they expect prices to fall, they wait.
Expected inflation up: shifts right
Confidence deserves special attention. It is not a number anyone controls, it can change fast, and it feeds on itself. People who fear redundancy spend less, which reduces firms’ revenue, which leads to actual redundancies, which frightens more people. Keynes called this force animal spirits, and you will meet it again when you get to his view of aggregate supply.
What moves investment
Determinant
How it works
Effect on AD
Interest rates
Most investment is financed by borrowing, so the interest rate is the price of the project. There is a broadly inverse relationship between rates and investment.
Rates up: shifts left
Business confidence
Firms invest when they expect a good return. A long run of growth breeds optimism, while a slowdown makes firms hold back and wait.
Confidence up: shifts right
Technology
New technology that cuts costs or raises output gives firms a reason to spend on capital they would otherwise not have bought.
New technology: shifts right
Business taxes
Higher taxes on profit leave less retained profit to fund investment and reduce the expected return on any project.
Business tax up: shifts left
Corporate debt
Firms already carrying heavy repayments have less spare cash and less appetite for borrowing more.
Debt up: shifts left
What moves government spending and net exports
Government spending is decided by people, not markets, and it moves for two kinds of reason. Political priorities differ: some governments believe the state should provide more, others believe it should be smaller. Economic priorities also matter: spending is set out in the annual budget and follows policy aims, so a government that has promised to upgrade the rail network has to spend to deliver it.
Net exports depend on three things:
Incomes of trading partners. When partner economies grow, their households buy more, including more of our exports, so X rises. When they fall into recession, X falls.
Exchange rates. If the domestic currency appreciates, our exports cost foreigners more and their goods cost us less, so X falls and M rises: net exports fall. A depreciation does the opposite.
Trade policy. More protection makes imports dearer and reduces M. Freer trade tends to raise both imports and exports.
The exchange rate one is worth practising, because it has two steps and students usually give one. An appreciation makes exports more expensive abroad and makes imports cheaper at home. Both effects push net exports down, so AD shifts left.
Putting it together
🧩 How to answer any “what happens to AD” question
Name the component affected. C, I, G or X − M.
Explain the mechanism in one sentence. Why does that component change?
State the direction of the shift and draw it, labelling AD1 and AD2.
Say what happens to real GDP and the price level at the new equilibrium.
Add a limitation if the question asks you to evaluate. Size of the component, time lags, or whether confidence follows.
Watch out for changes that pull in opposite directions. A rise in interest rates cuts C and I, but it also tends to attract foreign money, which strengthens the currency and cuts net exports too. Three components fall, so the answer is clear. But a currency depreciation raises net exports while making imported raw materials dearer, which is a supply-side effect. When two forces conflict, say so and explain which is likely to dominate.
WORKED EXAMPLE
Explain the effect on aggregate demand of a rise in the central bank’s interest rate. [4]
Step 1: consumption
Saving becomes more rewarding and mortgage and loan repayments rise, so households have less to spend and C falls.
Step 2: investmentborrowing costs rise, fewer projects are profitable, so I fallsStep 3: net exportsHigher rates tend to attract foreign capital, so the currency appreciates and net exports fall as well.Step 4: conclude with the diagramThree components fall, so AD shifts left, lowering real GDP and the price levelThree chains from a single change. That is a full-mark structure.
WORKED EXAMPLE
A country’s currency depreciates by 10%. Explain the likely effect on AD, and state one reason the effect might be smaller than expected. [4]
Step 1: exportsdomestic goods are cheaper for foreigners, so X risesStep 2: importsforeign goods cost more at home, so M fallsStep 3: net exports and ADNet exports rise, so AD shifts rightStep 4: a reason it may be limitedIf net exports are only a small share of AD, or if demand for exports is price inelastic in the short run, the shift will be modest. Imported raw materials also become dearer, which raises firms’ costs.
💡 Exam tip
Always route through a component. Never write “AD falls” without saying which part of AD fell and why.
Look for changes that hit more than one component. Interest rates hit three, and saying so is an easy extra mark.
Label the shift AD1 to AD2 with an arrow. Unlabelled shifts do not score.
Bring in the size of the component when evaluating. A big move in net exports may matter less than a small move in consumption.
Mention time lags. Firms do not respond to an interest rate change overnight, and that limits short-run effects.
Do not confuse a shift with a change in the price level. Check the trigger before you draw.
⚠️ Common mix-up
Confusing appreciation with depreciation. A stronger currency makes exports dearer and cuts net exports.
Thinking higher taxes always cut AD. If the government spends every extra pound it collects, G rises as C falls, and the net effect depends on the sizes.
Treating saving as spending. Saving is not part of AD. It is a leakage.
Assuming government spending only rises in recessions. It also rises because of political choices that have nothing to do with the cycle.
Confusing consumer confidence with actual income. They usually move together, but confidence can collapse before anyone loses a job.
Shifting AD for a cost change. Higher oil prices raise firms’ costs, which is a supply-side effect, not a demand-side one.
Up next: Short-Run Aggregate Supply, the other half of the model, and the reason the price level ends up where it does.
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