The long run aggregate supply curve represents the total quantity of goods and services an economy can produce when all resources are fully employed and prices and wages have had enough time to adjust fully. Worth adding: unlike short-term fluctuations driven by temporary shocks or changes in consumer confidence, this curve captures the economy’s sustainable production capacity over an extended period. Understanding the long run aggregate supply curve is essential for anyone studying macroeconomics, because it reveals the limits of growth, the role of productivity, and why demand-side stimulus cannot permanently increase output beyond its natural level.
What Is the Long Run Aggregate Supply Curve?
The long run aggregate supply curve, often abbreviated as LRAS, is a vertical line plotted at the economy’s potential output, also known as full-employment output or natural real GDP. It shows the level of real production that occurs when the labor market is in equilibrium, capital is fully utilized, and technology is being used efficiently Less friction, more output..
In graphical terms, the vertical axis measures the price level, while the horizontal axis measures real output. Because the LRAS is vertical, changes in the price level do not change the quantity of output supplied in the long run. Whether prices rise or fall, the economy returns to its potential output once all adjustments are complete Not complicated — just consistent. Simple as that..
This concept is rooted in classical economic thinking, which assumes that markets are self-correcting. Now, if there is unemployment, wages will eventually fall, making labor cheaper and encouraging firms to hire more workers. If there is inflation, input costs rise and squeeze profit margins, bringing production back down to its sustainable level.
Why Is the LRAS Curve Vertical?
The vertical shape of the long run aggregate supply curve reflects a fundamental idea: in the long run, output is determined by real factors, not by the price level. Those real factors include:
- The quantity and quality of labor
- The stock of physical capital such as machinery and infrastructure
- Availability of natural resources
- Technology and innovation
- Institutional and legal frameworks that support production and trade
Because these determinants do not change simply because the price level changes, the long run aggregate supply curve remains fixed at potential output. As an example, if the price level doubles overnight, workers will demand higher nominal wages to maintain their purchasing power. Practically speaking, once wages adjust, firms face the same real costs as before, and there is no incentive to produce more or less. The economy returns to the vertical LRAS line Simple, but easy to overlook. Worth knowing..
This flexibility of wages and prices is what separates the long run from the short run. In the short run, some prices and wages are sticky, meaning they do not adjust immediately. That stickiness gives the short run aggregate supply curve its upward slope. In the long run, however, stickiness disappears, and the economy gravitates back to its natural level of output.
LRAS vs SRAS: Key Differences
Students often confuse the long run aggregate supply curve with the short run aggregate supply curve. While both describe the relationship between the price level and real output, they behave very differently:
| Feature | Short Run Aggregate Supply (SRAS) | Long Run Aggregate Supply (LRAS) |
|---|---|---|
| Shape | Upward sloping | Vertical |
| Price and wage flexibility | Some prices and wages are sticky | All prices and wages are flexible |
| Output determinant | Temporary demand shocks, input price surprises | Productivity, resources, institutions |
| Response to price level | Higher prices encourage more output | No effect on output |
| Time horizon | Months to a few years | Several years to decades |
If aggregate demand increases in the short run, the SRAS curve shows that firms will increase output and prices will rise. In the long run, however, higher prices lead to higher wages and input costs, shifting SRAS back until output returns to the LRAS line. The end result is higher prices but the same real output Less friction, more output..
What Shifts the Long Run Aggregate Supply Curve?
Because the LRAS reflects the economy’s productive capacity, it only shifts when that capacity changes. A rightward shift indicates economic growth, while a leftward shift signals a contraction in potential output Worth knowing..
Factors That Shift LRAS to the Right
- Technological advancement: New inventions and better production methods allow more output from the same inputs.
- Increase in capital stock: More factories, equipment, and infrastructure expand what the economy can produce.
- Growth in the labor force: Population growth, immigration, or higher labor force participation adds workers.
- Improved human capital: Better education and training make workers more productive.
- Discovery of natural resources: New oil fields, minerals, or arable land expand resource availability.
- Institutional improvements: Stronger property rights, less corruption, and efficient regulations reduce the cost of doing business.
Factors That Shift LRAS to the Left
- Natural disasters: Earthquakes, floods, or pandemics can destroy capital and reduce labor availability.
- Decline in human capital: Poor education systems or brain drain reduce workforce quality.
- Resource depletion: Overuse of non-renewable resources limits future production.
- Worsening institutions: Political instability, excessive regulation, or weak rule of law discourage investment and production.
When policymakers talk about supply-side economics, they are usually referring to measures designed to shift the long run aggregate supply curve to the right, thereby increasing the economy’s long-term growth potential without causing inflation Easy to understand, harder to ignore..
Long Run Equilibrium and the Economy
Long run equilibrium occurs where the aggregate demand curve intersects both the short run aggregate supply curve and the long run aggregate supply curve at the same point. At this intersection, the economy is producing
