AP, IB, and College Microeconomic and Macroeconomic Principles 

Keys to Understanding Monopoly – AP/IB/College

Keys to Understanding the Monopoly Graph

Updated 7/26/2018 Jacob Reed
In the last review, we covered the perfectly competitive market structure. That is the most competitive of markets. Next, we will move on to the other extreme. Monopolies are the least competitive of markets. Review everything you need to know about monopolies on test day below.

Market structures spectrum

Like All Profit Maximizing Firms:

  • Produce the quantity where MR=MC
  • Price at Demand
  • Temporarily shut down when price falls below Average Variable Cost (AVC) at the profit maximizing quantity
  • Profit/loss is determined by the gap between the ATC and the firm’s demand curve at the profit maximizing quantity (MR=MC)

Monopoly:

Number of Sellers: One. There are no close substitutes and no competitors.

Product Difference: The product is unique.

Barriers to Entry: High barriers which prevent any competitors from entering. Monopolies may engage in rent seeking behavior (working to pass voter initiatives, lobbying politicians, etc), to maintain a monopoly. These actions will increase the firm’s ATC and erode some economic profits.

Long-run Profit: Due to the high barriers to entry, economic profit is possible in the long run.

Efficiency: No, Monopolies price above marginal cost and do not produce at the lowest average cost so they are not allocatively or productively efficient.

Economies of Scale: Monopolies usually capture economies of scale because the profit maximizing quantity is on the downward sloping portion of their long-run average total cost curve. 

Graph: Since there is only one firm, the market is the firm. As a result, the firms demand curve is downward sloping. The average revenue, and price will also be the demand curve (DARP). If the firm is a single price monopoly , the marginal revenue curve is below demand. 

Note: The cost curves for a monopoly are the same as a perfectly competitive firm and monopolistically competitive firm.  The AVC and AFC are rarely needed in this graph. 

Why is the marginal revenue below demand?

For a perfectly competitive firm (and a perfect price discriminating monopoly as seen below), marginal revenue is equal to demand. But for a single price monopoly (one that does not price discriminate), the marginal revenue is less than demand. That is because when the firm produces more output, it must lower the price of not just the last unit produced, but on all units produced. Take a look at the chart which shows the quantities of candy bars I could sell at each price (the demand is equal to the price). If I have one candy bar, I might be able to sell it for $3. But if I want to sell 2 candy bars, I must lower the price to $2.50; and since I am not a price discriminator, I charge the same price for both candy bars. As a result, the marginal revenue for that second candy bar isn’t the $2.50 I charged for it but just $2.00.

Total Revenue: As long as the marginal revenue curve is positive (above the x axis), total revenue is increasing as output increases. Since the marginal revenue curve is downward sloping, total revenue will increase at a decreasing rate. When marginal revenue is negative (below the x axis), total revenue decreases. So as output increases, a monopoly’s total revenue will increase at a decreasing rate, then decrease.

Marginal Revenue and Elasticity of Demand

The monopoly’s marginal revenue curve reveals the elasticity of the demand curve above. The total revenue test tells us the if a demand curve is elastic, a decrease in price will cause an increase in total revenue. At lower quantities monopoly’s marginal revenue curve is positive. That means as price falls with each additional unit produced, total revenue increases. Therefore, the demand curve is elastic at those quantities. When marginal revenue is zero (where it intersects the x axis), the demand curve is unit elastic at that quantity because the decrease in price causes no change in total revenue. Finally, at higher quantities, the marginal revenue curve is negative which indicates total revenue decreases with the price decrease. As a result, that portion of the demand curve is inelastic. Profit maximizing monopolies will always produce in the elastic region of their demand curve.

Regulation: Governments will sometimes regulate Monopolies by imposing price ceilings which are more efficient. A fair return price is one which enforces a price where economic profits are zero (P=ATC). The socially optimal price is allocatively efficient; where price equals marginal cost.

Compared to perfectly competitive markets: Unlike perfectly competitive firms, monopolies produce less, and price higher. Monopolies can also earn an economic profit in the long run. 

Higher Prices Lower Quantities
Price Discrimination: Price discrimination occurs when a firm is able to charge different customers different prices for the same product. Like letting kids eat free or giving senior citizens discounts at restaurants. Firms charge lower prices to people with a lower willingness to pay and higher prices to people with a higher willingness to pay. If the firm is able to figure the maximum price each customer is willing to pay and charge them that price, the firm would be a perfect price discriminator. That would cause the MR curve to be the same curve as the Demand, Average Revenue, and Price (MRDARP). Perfect price discriminators are allocatively efficient. The last unit produced will be priced at the marginal cost. ​

Multiple Choice Connections:
2012 Released AP Microeconomics Exam Questions: 8, 9, 21, 24, 44, 53
2008 Released AP Microeconomics Exam Questions: 39, 40, 51, 52, 53, 54, 58

Up Next: 
Review Game: Product Market Structures ReviewShading Practice, and Prices, Points, and Quantities
Graph Drawing Practice: Monopoly and Monopolistic Competition
Content Review Page: Monopolistic Competition

Other recommended resourcesACDC Leadership (Monopoly)