What Is Aggregate Demand?
Aggregate demand and supply
What you will learn
- Aggregate demand is planned spending on domestic output at each price level.
- Distinguish a movement along AD from a shift
Essential definitions
- Aggregate demand
- Total planned spending on domestically produced final goods and services at each general price level.
- Consumption
- Household expenditure on goods and services.
- Investment
- Expenditure on newly produced capital goods and additions to inventories.
Bring the spending components together
Aggregate demand, AD, means total planned spending on domestically produced final goods and services at each general price level. Its components are consumption, C; investment in new capital and inventories, I; government purchases, G; exports, X; and imports, M. AD = C + I + G + X − M. Subtract imports because their production occurs abroad.
In the diagram, real GDP is on the horizontal axis and the general price level on the vertical axis. AD slopes down. At a higher price level, money balances buy less, which may reduce consumption. Domestic products may also become dearer relative to foreign goods, reducing net exports. Interest-rate effects depend on monetary conditions. These explanations hold other spending determinants constant.
Why AD shifts
A change in the price level moves the economy along an existing AD curve. A change in spending at every price level shifts it. Suppose households expect more secure future incomes. They buy more at each price level, so AD shifts right from AD1 to AD2.
Consumption also depends on disposable income, wealth, debt, interest rates and expected future prices. Expected price rises may bring purchases forward. Investment depends on expected sales and profits, borrowing costs, technology and spare capacity; heavy business debt may restrain it. Government priorities determine purchases of services and infrastructure. Household taxes affect disposable income, and business taxes can affect investment returns.
Exports respond to overseas income and relative prices. Imports respond to domestic spending, exchange rates and trade rules. A tariff may cut some imports while raising input costs or provoking retaliation, so do not infer the overall AD change from one isolated component.
Connect demand to production
First identify the spending change. Then shift AD and examine where it meets aggregate supply, which the next lesson introduces. With spare capacity, stronger sales can lead firms to produce and hire more. Near capacity, extra spending is more likely to raise prices.
The calculation below adds spending in billions for one period. An initial increase in investment is not automatically the final GDP increase: extra income generates further spending, and supply conditions limit the response. A depreciation can support net exports but also make imported inputs dearer. Keep its demand and cost effects separate.
Hypothetical planned spending
- At a given price level, C = 300, I = 70, G = 90 and net exports = −10 billion. AD expenditure = 450 billion.
- An autonomous 20-billion increase in investment raises planned spending at that price level to 470 billion.
The initial expenditure increase shifts AD right; the final equilibrium GDP change also depends on supply and induced spending.
Aggregate demand: expansion and contraction
AD: P = 200 − 0.8Y. SRAS: P = 20 + 0.8Y. E2: Y=112.5, P=110.
Higher autonomous spending raises AD. With upward-sloping SRAS, firms expand output as the price level rises relative to sticky input costs. A fall in AD reverses this short-run result.
How to draw it and model assumptions
- Price level (index) vertically and real GDP (index) horizontally.
- Label AD₁, AD₂ and SRAS.
- Project E1 and E2 to both axes and show the AD shift with an arrow.
Hypothetical linear AD and SRAS; input prices and productive capacity fixed in the short run. A shift is a change in spending at each price level.
Apply and evaluate
- Interest sensitivity and confidence determine how strongly private spending responds to policy.
- Several components can move in opposite directions, so one component alone does not establish the net shift.
Common misconceptions
- A higher price level does not itself shift AD.
- An AD curve concerns the general price level, not the price of one individual product.
Knowledge check
Foreign incomes rise and demand for domestic exports increases. What shifts?
Real-world application
Energy costs and aggregate supply
16 November 2022: ONS reported that gas and electricity prices made the largest upward contribution to the change in UK annual consumer-price inflation between September and October 2022.
Model application: dearer energy can raise firms’ unit costs, shifting SRAS left. It also reduces households’ purchasing power, which can weaken demand. The observation alone does not identify the size of either shift or prove all inflation had one cause.
ONS, Consumer price inflation, UK: October 2022 ↗Historical evidence checked 9 October 2026. The model interpretation is an original teaching application.
What to remember
Aggregate demand is planned spending on domestic output at each price level. A price-level change moves along AD; a change in another spending determinant shifts the curve.
Completion is your own reflection on learning, not a test score. Syllabus references: 3.2.01, 3.2.02, 3.2.03, 3.2.04, 3.2.05, 3.2.06, 3.2.07.
Lessons in this section
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