Updated for the 2026-2027 CFA® Level I curriculum.
Monopolistic competition describes a market with many firms selling differentiated products. Each firm has some control over price because its product is not identical to a competitor's, but that control is limited by close substitutes. CFA Level I tests whether you can find a firm's profit-maximizing price and output, and whether you understand how short-run profit disappears in the long run. This note walks through the graph logic step by step.
Quick Answer
A monopolistically competitive firm faces a downward-sloping demand curve because its product is differentiated from competitors' products. The firm maximizes profit at the output where marginal revenue (MR) equals marginal cost (MC), then reads the price directly from the demand curve at that quantity. Because entry is relatively easy, short-run economic profit attracts new competitors, and economic profit tends to fall to zero in the long run. Even then, the firm keeps some pricing power and typically operates with excess capacity.
Key Takeaways
A monopolistically competitive firm's demand curve slopes downward because its product is differentiated, not identical to rivals' products.
MR lies below the demand curve because selling an extra unit requires a lower price on all units sold.
Profit-maximizing output ( ) occurs where , with rising through that point.
Price (P*) comes from the demand curve at , never from the curve and never set equal to .
Economic profit equals at the chosen output.
No single supply curve exists because quantity supplied depends on both cost and the firm's specific demand conditions.
In the long run, entry shifts demand curves inward until price equals , producing zero economic profit and excess capacity.
What You Need to Know for CFA Level I
Identify the defining characteristics of monopolistic competition: many firms, differentiated products, low entry barriers, limited pricing power.
Explain why the firm's demand curve slopes downward and why MR lies below it.
Locate optimal output where .
Read the profit-maximizing price from the demand curve at that output, not from .
Calculate or interpret economic profit using price, average total cost, and quantity.
Explain why monopolistic competition has no well-defined supply curve.
Compare short-run and long-run equilibrium, including zero economic profit and excess capacity.
What Is Monopolistic Competition?
Monopolistic competition sits between perfect competition and monopoly. Many firms compete, but each sells a product that differs from its rivals in some way. Entry barriers are relatively low, so new firms can enter when profit opportunities appear.
Products are close substitutes. A customer can switch from one coffee shop to another, but each shop still has some loyal customers who prefer its specific version. That loyalty gives each firm a small amount of pricing power.
Firms build differentiation through advertising, service quality, design, location, product features, and brand positioning. These choices shape how sensitive a firm's demand is to competitors' prices.
Demand and Marginal Revenue Under Monopolistic Competition
Each firm in monopolistic competition faces its own downward-sloping demand curve. This happens because the firm's product is not identical to its competitors' products. Some buyers prefer this firm's version even at a higher price, so the firm can raise price without losing every customer. It can also lower price to attract more buyers.
MR lies below the demand curve at every output level greater than one unit. To sell an additional unit, the firm must lower price. That lower price applies to all units sold, not just the marginal one. So each extra unit sold adds less revenue than the price charged for that unit.
The exact position of the demand curve depends on how successful the firm's differentiation is and how many close substitutes exist. Strong differentiation and few substitutes support a demand curve that is less sensitive to price changes. Weak differentiation and many substitutes make demand more price-sensitive.
How to Find the Profit-Maximizing Price and Output
Use this four-step process:
Step 1. Find where , with rising through that intersection.
Step 2. Move straight up from to the demand curve. The price at that point is .
Step 3. Compare to average total cost (ATC) at .
Step 4. Calculate economic profit when data allow.
Where:
is the profit-maximizing price read from the demand curve
is average total cost at output
is the output level where
Never set price equal to . That rule applies to firms in perfect competition, not to firms with downward-sloping demand curves. A monopolistically competitive firm's price always sits above at the profit-maximizing output.
Why There Is No Well-Defined Supply Curve
A supply curve maps each price to one specific quantity supplied. Monopolistic competition does not produce this clean relationship.
Output depends on two things at once: the firm's cost structure and its specific demand curve. Two firms with identical cost curves can choose different quantities at the same price if their demand curves differ. The same price can correspond to different quantities depending on how differentiated the product is and how demand shifts over time.
Because MC alone cannot predict quantity without knowing the position of demand, no single supply curve exists for a monopolistically competitive firm.
Short-Run Profit or Loss
Once you have and at , three outcomes are possible.
Condition | Outcome |
|---|---|
Positive economic profit | |
Firm breaks even | |
but | Firm operates at a short-run loss but continues producing |
If price falls below average variable cost ( ), the firm minimizes losses by shutting down. That decision follows the same logic used for any firm's shutdown point. For a full breakdown of that rule, see the related note on breakeven and shutdown decisions.
Monopolistic Competition in the Long Run
Short-run economic profit does not last. Low entry barriers allow new firms to enter the market when they see other firms earning profit.
As new firms enter, they pull customers away from existing firms. Each incumbent's demand curve shifts inward. This continues until price equals at the firm's chosen output. At that point, economic profit is zero.
The firm still applies the same rule: choose output where . What changes is the position of the demand curve, not the decision process.
Long-run equilibrium typically occurs to the left of the output that minimizes . This creates excess capacity. The firm produces less than the quantity that would minimize its per-unit cost, because it operates on the downward-sloping part of its demand curve rather than at the bottom of its curve.
Zero economic profit does not eliminate product differentiation. The firm still sells a distinct product and still charges a price above marginal cost. It simply cannot sustain profit above its opportunity cost of capital once entry catches up.
Product Differentiation and Pricing Strategy
Differentiation changes how buyers view substitutes. Strong differentiation makes buyers see fewer close alternatives, which makes demand less sensitive to price. This supports more pricing power.
Firms pursue non-price competition to strengthen this position. Advertising, product features, customer service, and brand image can all support demand. These choices also add cost. Higher marketing spending does not automatically raise profit. It raises profit only if the additional revenue from stronger demand exceeds the additional cost of achieving it.
Competitors respond to successful differentiation, and easy entry limits how long any pricing advantage lasts. Differentiation supports pricing power in the short run, but it does not guarantee permanent economic profit.
Worked Graph Example
Riverside Roasters sells a specialty coffee blend in a mid-sized city with several competing coffee shops. Each shop's blend differs slightly in taste and branding, so each faces its own downward-sloping demand curve.
Short-run data at the profit-maximizing output:
bags per month (point where )
per bag (read from the demand curve at )
ATC at is per bag
Step 1: Confirm is where .
Step 2: Read from the demand curve at that quantity.
Step 3: Compare to
Step 4: Calculate economic profit.
Plain-English interpretation: Riverside Roasters earns $2,800 in economic profit each month at its current price and output.
Long-run adjustment: This profit attracts new coffee shops into the neighborhood. As competitors open, Riverside's demand curve shifts inward. Over time, the demand curve moves until price equals ATC at the new profit-maximizing output. Suppose this settles at bags, where Economic profit falls to zero. Riverside still sells a differentiated product and still prices above marginal cost, but competition has erased the extra profit.
Common Exam Traps
Setting price equal to marginal cost. That rule belongs to perfect competition. A monopolistically competitive firm's price sits above at .
Reading price from the MR curve. Price always comes from the demand curve at , never from .
Treating MC as a supply curve. Quantity supplied depends on both cost and firm-specific demand, so no single MC-to-quantity mapping exists.
Assuming zero long-run profit means perfect competition. Zero economic profit can occur in both market structures, but monopolistic competition still involves product differentiation and price above marginal cost.
Forgetting excess capacity. Long-run equilibrium typically sits left of minimum . The firm does not produce at the cost-minimizing quantity.
Assuming differentiation guarantees lasting profit. Entry and competitor response limit how long any pricing advantage holds.
Practice Question
A monopolistically competitive firm has the following data at its current output: at units. The demand curve shows at . ATC at is .
What is the firm's profit-maximizing price and does it earn a short-run economic profit?
Price is $8, and the firm earns no economic profit because price equals marginal cost.
Price is $11, and the firm earns a short-run economic profit of $750.
Price is $9.50, and the firm breaks even because price equals average total cost.
Correct Answer: B
The firm sets output where MR = MC, which occurs at Q = 500. Price comes from the demand curve at that quantity, which is 11, not from MR or MC.
Option A. This confuses the output rule () with the perfect-competition pricing rule (). Monopolistically competitive firms price above marginal cost.
Option C. This mistakenly reads ATC as if it were the market price, ignoring the demand curve entirely.
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FAQs About Monopolistic Competition
How does a monopolistically competitive firm set price and output?
The firm finds output where equals , then reads price directly from its demand curve at that quantity. It never sets price equal to marginal cost. This two-step process applies in both the short run and the long run.
Why is the monopolistic competition demand curve downward sloping?
Each firm sells a differentiated product, so it has some control over price. Raising price loses some but not all customers, and lowering price attracts more buyers. This gives the firm a downward-sloping demand curve rather than a horizontal one.
Does monopolistic competition have a supply curve?
No. Quantity supplied depends on both the firm's cost structure and its specific demand curve. Because two firms with the same costs can supply different quantities at the same price, no single supply curve exists for this market structure.
What happens to economic profit in the long run?
Low entry barriers allow new firms to enter when incumbents earn economic profit. Entry shifts each firm's demand curve inward until price equals average total cost. Economic profit falls to zero, though firms still sell differentiated products and price above marginal cost.