Entry and Economic Profit in Monopolistic Competition

New substitutes shift each incumbent’s demand left.

Check Three Standard-Model Comparisons

These comparisons use the standard long-run model: differentiated close substitutes, relatively easy entry and exit, comparable firms and no continuing advantage that prevents rivals from competing away excess returns. Costs and other conditions are held fixed in the usual entry diagram. The zero-economic-profit endpoint is a model prediction under those assumptions, not a promise about the timing or income of a real business.

Trace Entry through the Incumbent’s Demand

Profit attracts entrants with differentiated alternatives. Each incumbent loses some customers at every price until its demand curve is tangent to ATC. At tangency, P=ATC, so economic profit is zero. The firm still chooses where MR=MC and still faces downward-sloping demand.

Separate Differentiation, Shifts and Elasticity

Entry supplies close substitutes rather than making all products identical. In the standard diagram, the incumbent sells less at a given price, so its demand shifts left. More alternatives can also make buyers more price-sensitive, but a leftward shift and an elasticity change are different claims. A firm-specific demand shift does not mean the industry’s total demand must have fallen. Check explicit and implicit costs before deciding whether excess returns remain.

Check Tangency at the Profit-Maximizing Output

At the chosen positive output, price is read from demand and average total cost is read at that same quantity. Their equality, P=ATC, gives zero economic profit. The profit-maximizing quantity also satisfies MR=MC in the smooth interior model. A demand–ATC intersection alone is insufficient: it need not be tangent or occur at a profit maximum. The usual long-run graph has no alternative positive output that earns excess profit.

Trace the Standard Exit Response

Loss causes exit, shifting the remaining firms’ demand right until normal profit returns. Entry and exit affect each firm’s demand, not merely the market supply curve used in perfect competition.

Read the Entry-and-Exit Reference

Apply the Model to a Differentiated Studio

Suppose a fitness studio earns positive economic profit and new yoga, cycling and training studios are feasible close substitutes. Under the stated model, entry reduces the original studio’s demand. Buyers may also become more price-sensitive as alternatives grow. The long-run endpoint covers economic cost without an excess return; the demand shift does not turn the studio’s differentiated service into an identical product.

Count a Normal Return Once

Economic cost includes the opportunity costs of the owner’s resources as well as explicit expenditure. A normal return is already included in that cost; do not add it a second time under another name. At zero economic profit, those resources receive their opportunity-cost return. Revenue can remain positive, and accounting profit can remain positive because accounting and economic cost measures differ.

Use the Right Market Diagram

Perfect competition handles entry differently: market supply shifts right while one firm’s horizontal demand line moves down with market price. In monopolistic competition, each firm has its own downward-sloping demand and new substitutes shift it left. Both reach zero economic profit, but the graph route and efficiency endpoint differ.

Check Whether Entry Is Feasible

If a binding barrier prevents new differentiated sellers, entry may not remove positive economic profit. Relatively easy entry is a necessary condition for the standard adjustment argument. A restriction can obstruct that process, but it does not by itself establish the number of firms or justify assigning a different market structure without further facts. Verify the entry condition before applying the zero-profit endpoint.

Avoid Inferring a Firm Count from One Graph

The exact number of firms is not determined by the basic graph. Market demand and each firm’s scale influence it. The key endpoint is tangency with no entry or exit incentive.

Distinguish One Tangency from Identical Curves

Long-run tangency occurs on the downward-sloping portion of the firm’s demand curve. It does not mean demand and ATC have equal slopes everywhere or that the firm produces at minimum ATC. The chosen point must also satisfy MR=MC.

Recheck Cost and Demand Conditions

Keep the standard exit diagram’s assumptions visible: fewer close substitutes shift the surviving firm’s demand right while its cost curves are held fixed. Real entry or exit can also affect input prices, technology or product quality; if a problem states such changes, include them rather than assuming every adjustment occurs through demand alone. Zero economic profit means no net profit-based incentive in this equilibrium, not a rule that no individual business can ever enter or leave.

Check the Entry and Normal-Return Definitions

OpenStax’s monopolistic-competition lesson explains how entry and exit affect a differentiated firm’s demand and why zero economic profit differs from zero accounting profit. The new cost summaries below are invented, internally consistent examples. They do not estimate a real studio’s income or predict how quickly entrants arrive.

Compare Accounting and Economic Profit

Before entry, an invented firm earns $228 of revenue in one period, pays $124 of explicit costs and uses owner resources with a separate $60 opportunity cost. After entry and the stated adjustment, its selected operating choice earns $165 of revenue with $105 of explicit costs and the same $60 opportunity cost. The $60 has not already been included in explicit costs. Find both profit measures in each situation.

Try Three Entry-and-Profit Questions

Connect Profit, Capacity and Marginal Decisions

Compare zero profit with markup and excess capacity, review the conditions for a marginal hiring decision, and continue through the CLEP Microeconomics learning hub.