How Does Fiscal Policy Change Aggregate Demand?
Fiscal policy
What you will learn
- Government purchases affect demand directly; taxes and transfers work through recipients' spending.
- Apply the model to an original scenario and justify its limits.
Essential definitions
- Discretionary fiscal action
- A deliberate change in spending or taxation made through a new policy decision.
- Fiscal stimulus
- An increase in public spending or reduction in taxes intended to support demand.
Trace the instrument to a spending component
Suppose the government orders repairs to public buildings. Payments to builders buy current output, so G rises directly. Builders pay workers and suppliers, who can spend some of their extra incomes. A household tax cut instead raises disposable income; consumption increases only to the extent households spend rather than save the cut.
Transfers work through recipients' responses too. Business-tax changes may alter investment returns, but firms need worthwhile projects and expected sales. Identify the policy instrument, the affected component and the reason spending changes before shifting aggregate demand.
Compare the models
Use real GDP horizontally and the price level vertically. Start at E1 where AD1 intersects supply. Expansion shifts AD right to AD2 and gives a new intersection E2. With idle resources in the flat Keynesian region, output and employment can rise with little price increase. Near capacity, more of the effect becomes higher prices.
In the neoclassical model, extra demand can temporarily move output above potential. Wages and costs then adjust, returning output to vertical LRAS unless productive capacity changes too. A completed infrastructure project may later shift supply right, but that requires an additional explanation about productivity; it is not the demand shift itself.
Explain contraction and choose conditions
Lower purchases or higher taxes can reduce AD. This can moderate excessive demand and inflation, at the cost of lower short-run output and employment. Cutting poorly used resources has different long-term effects from cancelling effective education or maintenance. The distribution of tax changes also affects how strongly consumption responds.
Consider a negative output gap of 4% with unemployed construction workers. Useful repairs can mobilise idle resources. The same programme during shortages may compete for scarce workers and mainly raise costs. Financing and implementation also matter, which the following HL and evaluation lessons examine. Select a policy according to the cause and stage of the problem rather than always favouring expansion.
Demand management: fiscal and monetary policy
AD: P = 180 − 0.8Y. SRAS: P = 20 + 0.8Y. E2: Y=100, P=100. The final equilibrium closes the initial gap at Yp=100.
Expansionary monetary or fiscal policy raises spending and AD; contractionary policy lowers it. Closing a recessionary gap can raise output and employment, while closing an inflationary gap restrains price pressure.
How to draw it and model assumptions
- Select the initial recessionary or inflationary position.
- Shift AD toward the intersection of SRAS and LRAS.
- Mark initial E1 and final E2; compare the price level and real output at these intersections.
Short-run upward SRAS; potential output fixed. Policy transmission, confidence, import leakages and time lags determine the size of the actual AD shift.
Keynesian aggregate supply
Initial AD: P = 130 − 0.8Y. Selected AD: P = 190 − 0.8Y. E2: Y=113.89, P=98.89, on the rising costs segment. Capacity is fixed at 120.
At low demand, unemployed factors allow output to rise with little pressure on costs. As bottlenecks emerge AS slopes upward; at full capacity further AD increases raise prices without raising output.
How to draw it and model assumptions
- Draw a flat, then rising, then vertical AS curve.
- Intersect each AD curve with the appropriate segment; mark initial E1 and new E2.
- Compare an identical demand increase at different initial levels of spare capacity.
Stylized three-section Keynesian curve; fixed capacity Y=120. Wage rigidity and weak demand can sustain underemployment equilibrium. This is not a vertical-LRAS adjustment model.
Apply and evaluate
- Estimate spare capacity and choose spending that can be implemented when support is needed.
Common misconceptions
- A tax cut does not guarantee an equal increase in consumption; households can save some of the gain.
Knowledge check
Why might fiscal stimulus have a larger real-output effect during a deep recession?
Real-world application
Separating the cycle from policy decisions
November 2024: CBO’s report on automatic stabilizers compares US federal budget balances with and without its estimated cyclical effects, alongside actual or projected output gaps.
Model application: a recession can lower tax receipts and increase unemployment-related spending even without a new policy vote. Therefore, a larger observed deficit does not by itself measure a discretionary stimulus. The counterfactual depends on estimates of potential output and is uncertain.
CBO, Effects of automatic stabilizers on the federal budget: 2024 to 2034 ↗Historical evidence checked 9 October 2026. The model interpretation is an original teaching application.
What to remember
Government purchases affect demand directly; taxes and transfers work through recipients' spending. The output and price effects depend on spare capacity, financing and timing.
Completion is your own reflection on learning, not a test score. Syllabus references: 3.6.04, 3.6.05.
Sources and applications
Lessons in this section
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