Difficulty: Intermediate | Prerequisites: Demand and Elasticity notes
Once you understand how demand works, the next question is what it costs to produce the goods people want to buy, and how the structure of the market shapes a firm's pricing power. This set of notes covers both sides: the cost curves that drive production decisions and the four main market structures that determine how much freedom a firm has when setting prices. Together, these concepts form the analytical core of managerial economics.
Costs behave differently in the short run (some inputs fixed) and the long run (all inputs variable). Marginal cost is the key figure for profit-maximising output decisions. The market structure a firm operates in (perfect competition, monopoly, oligopoly, or monopolistic competition) determines how much pricing power it has and how it should respond to competitors.
Short run
A time horizon in which at least one factor of production (typically capital, e.g. factory space or equipment) is fixed. The firm can vary labour and raw materials but cannot easily expand or shrink its plant. Think of it as the period where you are stuck with the factory you have.
Long run
A time horizon in which all factors of production are variable. The firm can build new plants, exit the market, or change its scale entirely. In simple terms, the long run is the planning horizon where nothing is locked in.
Fixed costs (FC)
Costs that do not change with the level of output. Rent, insurance premiums, salaried staff and loan repayments are typical examples. Even if output falls to zero, these costs remain.
Variable costs (VC)
Costs that change directly with the level of output. Raw materials, hourly wages and energy consumption are common examples. In simple terms, these are the costs you only incur because you are producing.
Total cost (TC)
The sum of fixed costs and variable costs: TC = FC + VC.
Marginal cost (MC)
The additional cost of producing one more unit of output. This is the figure managers compare against marginal revenue when deciding whether to produce that next unit.
Average total cost (ATC)
Total cost divided by quantity produced: ATC = TC / Q. The U-shaped ATC curve is one of the most important diagrams in the course.
Economies of scale
Cost advantages that arise when a firm increases its scale of production, causing long-run average cost to fall. Think of it as the reason large manufacturers can undercut smaller rivals on price.
Diseconomies of scale
Cost disadvantages that arise when a firm grows too large, causing long-run average cost to rise. Bureaucracy, coordination problems and communication breakdowns are typical causes.
Perfect competition
A market structure with many small firms selling identical (homogeneous) products. No single firm can influence the market price; each is a price taker.
Monopoly
A market structure with one dominant firm and high barriers to entry. The firm is a price maker and faces the entire market demand curve.
Oligopoly
A market structure with a small number of large firms whose decisions are interdependent. Each firm must consider how rivals will respond to its pricing and output choices.
Monopolistic competition
A market structure with many firms selling differentiated products. Each firm has some control over its price because its product is not identical to competitors' offerings. Think of it as the market for restaurants or clothing brands.
Price discrimination
Charging different prices to different consumers (or in different markets) for the same product, based on willingness to pay. Airlines, cinemas and software companies all practise this.
In the short run, the firm can only adjust variable inputs (labour, materials). Capital is fixed.
The law of diminishing marginal returns applies in the short run: as you add more of a variable input to a fixed input, the marginal product of the variable input eventually declines.
In the long run, all inputs are adjustable. The firm chooses the combination of capital and labour that minimises cost for any given output level.
TC = FC + VC: total cost is the vertical sum of the fixed and variable cost curves.
ATC = TC / Q: average total cost per unit. Falls at first (spreading fixed costs over more units), then rises (diminishing returns push up variable costs per unit). This gives the ATC curve its characteristic U shape.
AVC = VC / Q: average variable cost. Also U-shaped, but always below ATC (because ATC includes the fixed-cost component).
AFC = FC / Q: average fixed cost. Falls continuously as output rises (the same fixed cost spread over more units).
MC = ΔTC / ΔQ: marginal cost. Intersects both ATC and AVC at their minimum points. This is a favourite exam diagram.
Produce where marginal revenue (MR) equals marginal cost (MC), provided price covers average variable cost.
If P < AVC, the firm should shut down in the short run (it cannot even cover its variable costs).
If AVC < P < ATC, the firm operates at a loss but continues in the short run (it covers variable costs and part of fixed costs).
Economies of scale: bulk purchasing discounts, specialisation of labour, spreading fixed costs, access to cheaper capital.
Diseconomies of scale: managerial inefficiency, communication problems, slower decision-making.
The long-run average cost (LRAC) curve is the envelope of all short-run ATC curves and is also U-shaped (or sometimes L-shaped in practice).
Minimum efficient scale (MES): the smallest output at which LRAC is minimised. Industries with high MES tend to have fewer firms (think car manufacturing vs. hairdressing).
Many small firms, homogeneous product, free entry and exit, perfect information.
Each firm is a price taker: it faces a perfectly elastic (horizontal) demand curve at the market price.
Profit maximisation: produce where P = MC.
In long-run equilibrium, economic profit is zero (P = ATC at the profit-maximising output).
Single seller, unique product, high barriers to entry (patents, control of resources, legal restrictions).
The firm faces the entire downward-sloping market demand curve and is a price maker.
MR < P for a monopolist (to sell more, it must lower the price on all units).
Profit maximisation: produce where MR = MC, then charge the price on the demand curve at that quantity.
Monopolies can earn long-run economic profit because barriers prevent entry.
Deadweight loss arises because the monopolist produces less than the socially optimal quantity.
Few large firms, products may be homogeneous or differentiated, significant barriers to entry.
Key feature: interdependence. Each firm's optimal strategy depends on what rivals do.
Models of oligopoly behaviour:
Cournot: firms choose quantities simultaneously.
Bertrand: firms choose prices simultaneously.
Stackelberg: one firm moves first (leader), others follow.
Kinked demand curve: explains price rigidity in oligopolies.
Collusion and cartels: firms may cooperate to restrict output and raise prices (illegal in most jurisdictions, but it happens).
Many firms, differentiated products, low barriers to entry.
Each firm has a downward-sloping demand curve (because its product is slightly different from rivals').
Short-run profits attract new entrants; in long-run equilibrium, economic profit is zero.
Firms compete on product differentiation, branding and advertising rather than price alone.
Cost-plus pricing: add a standard markup to average cost. Simple but ignores demand conditions.
Price discrimination: charge different prices based on willingness to pay. First-degree (perfect), second-degree (quantity discounts), third-degree (student discounts, peak vs. off-peak).
Penetration pricing: set a low initial price to gain market share, then raise it later.
Price skimming: set a high initial price to capture consumers with high willingness to pay, then lower it gradually.
Bundling: sell multiple products together at a combined price lower than the sum of individual prices.
TC = FC + VCATC = \frac{TC}{Q} \quad AVC = \frac{VC}{Q} \quad AFC = \frac{FC}{Q}MC = \frac{\Delta TC}{\Delta Q}\text{Profit} = TR - TC = (P \times Q) - TCProfit-maximising condition: produce where MR = MC (and P ≥ AVC in the short run).
The short-run / long-run distinction is exactly why a restaurant might stay open during a slow winter season even when it loses money: it still covers rent (a fixed cost it pays regardless) by earning enough to cover food and wages. Closing would not eliminate the lease payment.
Price discrimination is visible everywhere. Cinemas charge less for matinees (off-peak pricing). Software firms offer student editions at steep discounts. Airlines show different fares to different browsers. In each case the firm segments consumers by willingness to pay.
Students often confuse marginal cost with average cost. MC is the cost of the next unit; ATC is cost per unit across all units produced. They are equal only at ATC's minimum.
Students sometimes think monopolists can charge any price they like. They cannot. They are constrained by the demand curve: a higher price means fewer units sold.
Students mix up the shutdown rule. The relevant comparison in the short run is P vs. AVC, not P vs. ATC. A firm can rationally operate at a loss as long as price exceeds average variable cost.
Students assume oligopoly always means collusion. Many oligopolies compete fiercely; interdependence does not require cooperation.
⚠️ The MR = MC rule for profit maximisation appears in nearly every exam. Be prepared to apply it across all four market structures.
⚠️ Drawing and interpreting cost curves (MC intersecting ATC and AVC at their minima) is a common diagram question.
⚠️ Comparing long-run outcomes across market structures (zero profit in perfect competition and monopolistic competition vs. positive profit in monopoly) is a staple essay topic.
⚠️ Calculation questions often give you TC and TR functions and ask for the profit-maximising Q. Set MR = MC and solve.
True or false: In perfect competition, firms are price makers. (False, they are price takers)
Fill in the blank: The shutdown condition in the short run is when price falls below _______. (Average variable cost, AVC)
True or false: Marginal cost intersects average total cost at ATC's maximum point. (False, at its minimum)
Fill in the blank: A monopolist maximises profit by producing where _______ = _______. (MR = MC)
True or false: In long-run equilibrium under monopolistic competition, firms earn positive economic profit. (False, zero economic profit)
Q: Given total cost TC = 100 + 5Q and total revenue TR = 10Q, find the output level that maximises profit.
A: Profit = TR - TC = 10Q - (100 + 5Q) = 5Q - 100. This is a linear function that increases with Q, so profit is maximised at the highest feasible Q. However, if this is a competitive firm, MR = 10 and MC = 5 (the derivative of TC with respect to Q). Since MR > MC for all units, the firm produces as much as it can. In a more realistic exam setting, a quadratic TC function would yield a finite answer where MR = MC.
Q: Differentiate between perfect competition and monopolistic competition in terms of product differentiation and price control.
A: In perfect competition, products are homogeneous (identical), so no firm has any price control; each is a price taker. In monopolistic competition, products are differentiated (branding, quality, features), giving each firm a downward-sloping demand curve and some degree of price control. The key trade-off is that differentiation provides pricing power but also means firms spend on advertising and branding.
Q: Why might a firm operating at a loss in the short run choose to continue producing rather than shutting down?
A: If price exceeds average variable cost (P > AVC), the firm covers all its variable costs and contributes something toward fixed costs. Shutting down would mean paying all fixed costs with zero revenue. Continuing to produce reduces the overall loss.
Q: Explain why a monopolist produces a lower quantity and charges a higher price than a perfectly competitive market would.
A: A monopolist restricts output to the point where MR = MC, and MR lies below the demand curve (because lowering price to sell more applies to all units). In perfect competition, output expands to where P = MC. Since the monopolist's MR < P, its profit-maximising quantity is lower and its price is higher, creating deadweight loss.
This connects to Demand and Elasticity because a firm's pricing power depends on the elasticity of demand it faces, which in turn depends on market structure. It also connects to Game Theory and Strategy: oligopoly pricing decisions are strategic interactions best analysed with game-theoretic tools like the payoff matrix and Nash equilibrium.
Fixed costs, variable costs, total cost, marginal cost, average total cost, ATC, AVC, AFC, economies of scale, diseconomies of scale, LRAC, minimum efficient scale, MES, perfect competition, monopoly, oligopoly, monopolistic competition, price taker, price maker, MR = MC, shutdown rule, cost-plus pricing, price discrimination, penetration pricing, price skimming, bundling, Cournot, Bertrand, Stackelberg, kinked demand curve, barriers to entry, deadweight loss, managerial economics MGT 301