Difficulty: Intermediate | Prerequisites: Basic cost concepts (total cost, average cost), understanding of supply and demand.
This topic covers how firms make production and pricing decisions. It brings together cost analysis (short run and long run), the profit-maximisation rule, and pricing strategies like price discrimination. These concepts apply across all market structures and form the supply-side toolkit for intermediate microeconomics. If you are comfortable with the distinction between fixed and variable costs, you have the foundation.
Firms maximise profit by producing where marginal revenue equals marginal cost, regardless of market structure. In the short run, at least one input is fixed, which constrains decisions; in the long run, everything is adjustable. Pricing strategies like price discrimination and competitive price-matching are tools firms use to navigate their specific market conditions.
Marginal cost (MC)
The additional cost of producing one more unit of output, calculated as the change in total cost divided by the change in quantity: MC = ΔTC / ΔQ.
In simple terms: how much it costs you to make one more widget. Early on it might fall (you are getting more efficient), but eventually it rises (you are stretching your resources thin).
Short run
A time period in which at least one input (typically capital, such as factory size or major equipment) is fixed and cannot be changed.
Think of it as the period where you are stuck with what you have. You can hire more workers, but you cannot build a new factory overnight.
Long run
A time period long enough that all inputs are variable. The firm can change its plant size, adopt new technology, or exit the market entirely.
In simple terms: the planning horizon where nothing is locked in and everything is up for reconsideration.
Fixed inputs
Inputs that cannot be changed in the short run, such as a factory building, a long-term lease, or specialised machinery.
Think of it as the things you are contractually or physically committed to, regardless of how much you produce.
Variable inputs
Inputs that can be adjusted in the short run, such as labour hours, raw materials, or electricity usage.
In simple terms: the stuff you can turn up or down fairly quickly as production needs change.
Total revenue (TR)
The total income a firm receives from selling its output: TR = Price × Quantity.
Marginal revenue (MR)
The additional revenue generated by selling one more unit of output.
In simple terms: how much extra money comes in from the next sale. For a price taker, MR equals the market price. For a firm with market power, MR is less than price because selling one more unit requires lowering the price on all units.
Price discrimination
Charging different prices to different customers for the same product, based on differences in willingness to pay and demand elasticity.
Think of it as charging more to the customer who will pay more, and offering a discount to the one who is price-sensitive, so you capture revenue from both.
Technological change
Improvements in products or production processes, including new equipment, automation, and redesigned workflows.
In simple terms: anything that lets you make more with less, or make something better than before.
Economies of scale
Cost advantages that arise when a firm increases its scale of production, leading to a lower average cost per unit.
Think of it as buying in bulk: the more you produce, the cheaper each unit becomes, up to a point.
In the short run, at least one input is fixed. The firm can adjust variable inputs (labour, raw materials) but cannot change its plant size, major equipment, or technology.
In the long run, all inputs are variable. The firm can expand, shrink, adopt new production methods, enter new markets, or exit entirely.
The boundary between short run and long run is not a fixed calendar period. It varies by industry: a software company can scale up in weeks; a steel mill may need years to build a new plant.
Short-run decisions focus on how to use existing capacity efficiently. Long-run decisions focus on what capacity to build.
MC = ΔTC / ΔQ. It measures the cost of producing one additional unit.
The typical MC curve is U-shaped:
Initially falls as the firm benefits from specialisation and increasing returns (workers become more efficient with repetition, fixed costs are spread over more units).
Eventually rises due to diminishing returns: adding more of a variable input to a fixed input yields progressively smaller increases in output, pushing up the cost per additional unit.
The MC curve is central to production decisions. The profit-maximising output is always found on the MC curve.
The universal rule: produce where marginal revenue equals marginal cost.
If MR > MC, the firm should produce more: each additional unit adds more to revenue than to cost.
If MR < MC, the firm should produce less: each additional unit costs more than it earns.
This rule applies to every market structure. What differs is how MR relates to price:
Perfect competition: MR = P (constant).
Monopoly and monopolistic competition: MR < P (decreasing), because selling more requires lowering the price.
Firms with market power can increase profits by charging different prices to different customer groups.
Two conditions are required:
The firm must be able to identify groups with different demand elasticities (different willingness to pay).
The firm must be able to prevent resale (arbitrage) between groups.
The logic: charge higher prices to customers with inelastic demand (they will pay anyway) and lower prices to those with elastic demand (they would otherwise walk away). This extracts more consumer surplus than a single uniform price.
Examples include student discounts, airline pricing (business vs economy class), and software licensing tiers.
Technological progress can be incremental (upgrading machinery, improving workflows) or radical (automating entire production lines, creating new product categories).
Effects: increased productivity, lower costs per unit, and sometimes the creation of entirely new markets.
Technological change shifts cost curves downward, allowing firms to produce more at lower cost and potentially gain competitive advantage.
In markets with intense competition, firms adopt strategies to retain customers while protecting margins.
Walmart's approach: match prices from major online competitors (especially Amazon) but not from local brick-and-mortar stores. The reasoning is that online shopping has greater price transparency, so customers who comparison-shop digitally will switch if prices are not matched. Local retail competition is less price-transparent.
This reflects a broader principle: firms price-match most aggressively in the channel where competition is most visible and customer switching is easiest.
Marginal cost
MC = ΔTC / ΔQ
Total revenue
TR = P × Q
Profit
Profit = TR - TC = (P × Q) - TC
Marginal revenue for a price taker
MR = P (constant, equal to the market price)
Marginal revenue for a firm with market power
MR < P and MR decreases as output increases. The firm must lower price on all units to sell one more, so the revenue gained from the additional unit is less than its price.
Relationship between elasticity and MR
MR = P × (1 + 1/Ed), where Ed is the price elasticity of demand (a negative number). When demand is elastic (|Ed| > 1), MR is positive. When demand is inelastic (|Ed| < 1), MR is negative.
Manufacturing plants vs service firms illustrate the short-run/long-run distinction. A car manufacturer may need three to five years to build a new assembly plant (long short run). A consultancy can hire new staff and rent additional office space in weeks (short short run). The calendar length of "the short run" is entirely industry-specific.
Walmart's selective price-matching shows competitive pricing in practice. Online prices are matched because that is where competition is fiercest and most transparent. In-store prices are not matched against local competitors because shoppers in physical stores are less likely to comparison-shop in real time.
Regulated utilities demonstrate price discrimination by regulators on behalf of consumers. Electricity companies often charge different rates for peak and off-peak usage, effectively segmenting customers by their demand elasticity at different times of day.
Students often think marginal cost always rises. It does not. MC typically falls first (specialisation gains, spreading fixed costs) before rising (diminishing returns). The U-shape matters.
Students often confuse the short run with a specific calendar period (e.g. "less than one year"). The short run is defined by whether at least one input is fixed, and that varies enormously across industries.
Students often assume price discrimination is illegal or unethical. It is legal in most contexts and is practised widely (student discounts, early-bird pricing, tiered subscriptions). It is distinct from illegal practices like price fixing.
Students often think profit maximisation means charging the highest possible price. It does not. Profit is maximised at the output where MR = MC, and the corresponding price is read off the demand curve. Charging above that price would reduce quantity demanded and lower total profit.
⚠️ The MR = MC rule is the single most tested concept in firm theory. Be able to apply it, explain it, and draw it for both price takers and price makers.
⚠️ Know the two conditions for successful price discrimination (identify different elasticities, prevent resale). This is a common short-answer or multiple-choice question.
⚠️ Be clear on why MC curves are U-shaped. Explain both the falling portion (specialisation, spreading fixed costs) and the rising portion (diminishing returns). Exams may ask you to explain one or both.
⚠️ Understand the short-run/long-run distinction as a concept, not as a fixed time period. A question that asks "In the short run, which inputs can a firm adjust?" is testing whether you know that only variable inputs can change.
⚠️ Be prepared to explain how a price cut affects total revenue differently depending on demand elasticity. This ties together the pricing and elasticity material.
Fill in the blank: Marginal cost is calculated as ΔTC divided by _______. (ΔQ, the change in quantity produced.)
True or False: In the short run, a firm can change its factory size. (False: factory size is typically a fixed input in the short run.)
Fill in the blank: A price taker's marginal revenue equals _______. (The market price, P.)
True or False: Price discrimination requires that the firm can prevent resale between customer groups. (True.)
True or False: Marginal cost always increases as output rises. (False: MC typically falls first due to specialisation, then rises due to diminishing returns.)
Q: Explain why the marginal cost curve is typically U-shaped.
A: MC initially falls because of specialisation and spreading fixed costs over more units (increasing marginal returns). It eventually rises because of diminishing marginal returns: as more of a variable input (e.g. labour) is added to a fixed input (e.g. a factory), each additional worker contributes less to output, so the cost of each additional unit of output increases.
Q: A monopolist currently produces at a point where MR > MC. Should it increase or decrease output? Explain.
A: It should increase output. Each additional unit adds more to revenue (MR) than to cost (MC), so producing more raises total profit. It should keep expanding until MR = MC.
Q: Why does a price taker's MR equal the market price, while a monopolist's MR is less than price?
A: A price taker is too small to affect the market price, so selling one more unit brings in exactly the market price. A monopolist faces the entire market demand curve: to sell one more unit, it must lower the price on all units it sells, so the revenue gained from the extra unit is less than its price.
Q: Give one example of price discrimination and state the two conditions it requires.
A: Airlines charge higher fares to business travellers (inelastic demand, low flexibility) and lower fares to leisure travellers who book early (elastic demand, high flexibility). The two conditions: the firm must identify groups with different elasticities, and it must prevent resale (a business traveller cannot buy a discount leisure ticket and use it for a business trip, because restrictions like advance-purchase requirements and Saturday-night stays make resale impractical).
Firm cost analysis provides the supply-side foundation for the market structures covered in the companion notes. The profit-maximisation rule (MR = MC) is applied differently in each structure but is always the same underlying principle. Consumer choice theory (companion notes on Consumer Behaviour) provides the demand side. Together, these three topics form the core of intermediate microeconomics.
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