Aggregate Supply: What It Is, How It Works

The 4 Factors of Production, Supply Curve, Law of Supply and Demand

business meeting
Entrepreneurship contributes to aggregate supply. Photo: Jon Feingersh/Getty Images

Defintion: Aggregate supply is the total of all goods and services produced by an economy over a given period. When people talk about supply in the U.S. economy, they are usually referring to aggregate supply. The typical time frame is a year.

That time frame is important because supply changes more slowly than demand. For example, demand can rise quickly, but companies can't ramp up production as fast.

When demand drops, it can take companies months to reduce supply.  They've got to close factories and lay off workers.

That's why there's a big difference between supply in the short-run versus the long-run. Short-run supply depends on price. As demand rises, customers are willing to pay a higher price. Businesses will increase supply to gain the profits from higher prices until they reach their current capacity.

In the long-run, if the price and demand remain high, companies can boost supply. They have the time to add the workers, machinery, and factories required. (Source: "Aggregate Supply,",)

The amount supplied is determined by the four factors of supply. The amount supplied is called the natural rate of output. Short-run economic fluctuations can occur without affecting the long-run output rate. The United States has an abundance of the factors of production. That allows American companies to produce 20% of the world's supply.

The following four factors determine long-run supply.

  1. Labor. The people who work for a living. The value of labor depends on workers' education, skills, and motivation. The reward or income for labor is wages. The United States has a large, skilled and mobile labor force that responds quickly to changing business needs. But it faces increasing competitive labor from other countries. For more, see Why American Jobs Are Being Outsourced.
  1. Capital Goods. Man-made objects, such as machinery and equipment, that are used in production. The United States is a technological innovator in creating capital goods, from airplanes to robots. The income derived from capital goods is interest.
  2. Natural Resources. The raw goods and materials used by labor to create supply. The United States has a unique combination of easily-accessible land and water. It has a moderate climate, miles of coastline and lots of oil. The income from this is rent.
  3. Entrepreneurship. The drive of business owners to produce and innovate. The income from this is profits.

Financial capital, such as money and credit, is not a factor of production. Instead, it's used to buy the factors of production. In other words, it isn't itself a component of anything produced. But the ease of obtaining financial capital, whether through stocks, bonds, or loans, plays a critical role in supply. One of the reasons the U.S. economy is so powerful is the ease of obtaining financial capital. (Source: St. Louis Federal Reserve, Factors of Production)  

Aggregate Supply Curve

The supply curve charts out how much will be supplied based on the price. Here's how it works. If someone asks you, "How much will you supply?" you would first ask them, "How much will you pay me?" If that answer were satisfactory, you'd ask, "How long have I got?" In other words, your answer would vary depending on the price and the time frame.

That's what the supply curve describes. The higher the price and the longer the time-frame, the more you would produce. That's why a normal supply curve slopes up to the right. An aggregate supply curve simply adds up the supply curves for every producer in the country.

Aggregate Supply and Aggregate Demand

Of course, you and the person would have to agree on both the price and the deadline. In other words, that persona's demand curve would have to intersect with your supply curve. When all the demand for everything in the country is added together, that's aggregate demand. Everything in an economy depends on how these curves intersect.

Law of Supply and Demand

The amount supplied is guided by the laws of supply and demand. The law of supply says that supply increases when the price increases. The law of demand says that demand decreases as the price increase. The right price is when the amount supplied equals the amount demanded.

In other words, an economy must follow these six rules:

  1. Supply must equal demand.
  2. Demand creates supply, but supply won't create demand.
  3. Prices adjust until supply equals demand.
  4. When prices decline, businesses either a) decrease supply, b) lower the operating costs to maintain profit margins, c) go out of business, thus reducing output.
  5. When prices rise, businesses supply more in the short-term until they reach current capacity. In the long-run, they increase the factors of production so they can supply more. They may also create similar or related products to meet the demand.
  6. If supply is constrained, then prices will continue to rise, creating inflation.

What Does the U.S. Supply?

The amount supplied is the output. It's measured by Gross Domestic Product (GDP.) The four components of GDP are:

  1. Personal Consumption. It's nearly 70 percent of total supply. It includes goods (such as automobiles and appliances) and services (such as healthcare and banking.)
  2. Business investment. That includes machinery and equipment. This category also includes construction.
  3. Government spending. Most of this is Social Security, defense, and Medicare.
  4. Net exports. Most of this is capital goods, such as machinery and equipment, and consumer goods, especially pharmaceuticals. For more, see Import/Export Components