3.4 Long-Run Aggregate Supply (LRAS)

Long-run aggregate supply (LRAS) shows the total output an economy can produce when all resources are fully employed. It is a vertical line at the full-employment level of real GDP (often labeled Y or YF), because in the long run wages and prices fully adjust.

LRAS Macroeconomics

In macroeconomics, long-run aggregate supply (LRAS) is the economy's full-employment level of real output. The LRAS curve is vertical because in the long run wages and prices fully adjust, so a higher price level does not increase sustainable real GDP.

For AP Macro 3.4, connect LRAS to productive capacity. Anything that expands the economy's ability to produce, like more resources, better technology, or higher productivity, shifts LRAS right. Anything that lowers productive capacity shifts LRAS left.

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Why This Matters for the AP Macroeconomics Exam

LRAS is part of the aggregate demand-aggregate supply model, which is one of the most heavily used tools in AP Macroeconomics. You need to know what makes the long run different from the short run, why the LRAS curve is vertical, and what causes it to shift. This shows up when you interpret AD-AS graphs, identify whether an economy is at, above, or below full employment, and explain how the economy adjusts over time. Getting comfortable with LRAS now sets you up for later topics like long-run self-adjustment and economic growth.

Key Takeaways

• In the short run, some input prices (especially wages) are fixed or slow to adjust. In the long run, all wages and prices are fully flexible.
• The LRAS curve is vertical at the full-employment level of real GDP because output does not change when the price level changes once wages and prices fully adjust.
• LRAS represents maximum sustainable capacity, the same idea shown by the production possibilities curve (PPC). A rightward LRAS shift pairs with the PPC expanding outward and economic growth.
• Because wages and prices fully adjust in the long run, there is no long-run trade-off between inflation and unemployment, and the economy returns to the natural rate of unemployment.
• LRAS shifts when the quantity or quality of resources changes, or when policies change the economy's productive capacity. A leftward shift means the economy can produce less; a rightward shift means it can produce more.

What the LRAS Curve Shows

Long-run aggregate supply is the amount of goods and services an economy can produce when all resources are fully employed. This is also called potential output or full-employment output.

The key to LRAS is the difference between the short run and the long run:

• Short run: some input prices, especially wages, are fixed or slow to adjust.
• Long run: all prices and wages are fully flexible and adjust to changes in the economy.

In the long run, the relationship between the price level and real GDP supplied is constant. As the price level rises or falls, firms do not change the quantity of real GDP they produce. That is because when the price level increases, wages and resource prices increase by the same amount, so there is no incentive to produce more or less.

Because wages and prices fully adjust this way, there is no long-run trade-off between inflation and unemployment. In the long run, the economy returns to the natural rate of unemployment.

Why the Curve Is Vertical

The LRAS curve is vertical at the full-employment level of output. YF (or Y*) represents the quantity of output a society can produce when it is at full employment and at the natural rate of unemployment.

Maximum sustainable capacity is the total output an economy can produce over a set period of time when all resources are fully employed. The LRAS curve corresponds to the production possibilities curve (PPC) because both represent this maximum sustainable capacity. When you see LRAS shifting to the right, you can pair it with the PPC expanding outward and with economic growth.

When you graph this in the AD-AS model, remember to label the axes "Price Level" and "Real GDP," not "Price" and "Quantity." That mix-up is an easy way to lose points.

What Shifts LRAS

LRAS shifts any time something would also shift the production possibilities curve. The difference between an SRAS shift and an LRAS shift is what you are changing: LRAS changes the potential output of the economy, while SRAS changes actual output at the current time.

LRAS shifts when there is a change in:

• The number of resources (factors of production), such as a larger labor force, more capital, or more natural resources.
• The quality of resources, such as better technology that raises the productivity of labor and capital.
• Policy, such as incentives that increase employment or investment.

Any of these can increase potential output and shift LRAS right, or decrease potential output and shift LRAS left.

Changes in the Number of Resources

This category includes changes in:

• The size of the workforce
• The amount of land or natural resources available
• The capital stock

Things that increase LRAS: a larger workforce, an increase in land resources, an increase in capital stock.

Things that decrease LRAS: a smaller workforce or population, depletion of land resources, destruction of capital.

Changes in the Quality of Resources

This category includes:

• A better educated and more highly skilled workforce
• An improvement in the quality of land resources
• An improvement in capital

Greater investment in schools and job training gives the workforce more productive skills. New technology that makes resources more productive raises potential output. For example, improvements that increase yields or improve capital can shift LRAS right. On the other side, if a country's infrastructure or education system deteriorates, potential output can decrease.

Policy Changes

Policy changes can also shift potential output, often through different levels of government. For example, if the government creates strong incentives to find work, the workforce can grow and LRAS increases. Tax incentives to invest in capital or technology can also raise potential output. Treat these as applications of how policy can affect productive capacity, not as a fixed list you must memorize.

How to Use This on the AP Macroeconomics Exam

Multiple Choice

• Identify the LRAS curve as vertical at full-employment output and know that price level changes do not move output along LRAS.
• Connect LRAS to the natural rate of unemployment and to the idea that there is no long-run trade-off between inflation and unemployment.
• Recognize that a rightward LRAS shift means economic growth and an outward PPC shift.

Free Response

• When asked to draw the AD-AS model, label axes "Price Level" and "Real GDP" and mark full-employment output on the LRAS curve.
• If a prompt describes more resources, better technology, or growth-friendly policy, show LRAS shifting right. For lost resources or declining capacity, show it shifting left.
• Be ready to explain why output stays the same along LRAS when the price level changes: wages and prices fully adjust.

Common Trap

• Do not confuse a shift of LRAS (a change in potential output) with a movement along SRAS (a change in actual output at current prices).

Common Misconceptions

• LRAS is not upward-sloping like SRAS. It is vertical because in the long run wages and prices fully adjust, so output does not respond to price level changes.
• A higher price level does not raise long-run output. Along LRAS, more inflation does not buy more real GDP.
• LRAS and SRAS are different curves. LRAS is about potential output (maximum sustainable capacity), while SRAS is about actual output when some input prices are still fixed.
• A rightward LRAS shift is the same idea as economic growth and an outward PPC shift, not just a temporary boost in output.
• The AD-AS graph is not the same as a single-market supply and demand graph. Use "Price Level" and "Real GDP" on the axes, not "Price" and "Quantity."

Related AP Macroeconomics Guides

• 3.1 Aggregate Demand
• 3.2 Spending and Tax Multipliers
• 3.3 Short-Run Aggregate Supply (SRAS)
• 3.8 Fiscal Policy
• 3.5 Equilibrium in Aggregate Demand-Aggregate Supply (AD-AS) Model
• 3.6 Changes in the AD-AS Model in the Short Run