What is the difference between normal profit and supernormal profit?

Normal profit is the minimum level of profit required to keep a firm in business in the long run; it is considered a cost because it represents the opportunity cost of the entrepreneur's time and capital. Supernormal profit (or abnormal profit) is any profit above normal profit, earned when total revenue exceeds total costs including normal profit. In perfect competition, supernormal profit attracts new firms into the market, driving prices down until only normal profit remains.

Why is the marginal cost curve U-shaped?

The marginal cost curve is U-shaped due to the law of diminishing returns. Initially, as a firm hires more variable factors (e.g., labour), specialisation and division of labour cause marginal product to rise, reducing marginal cost. Eventually, diminishing returns set in: each additional worker adds less to output, so marginal cost rises. This creates the typical U-shape, with MC falling then rising.

How do you calculate profit from a diagram?

On a cost and revenue diagram, profit is the area between the average revenue (AR) curve and the average total cost (ATC) curve at the profit-maximising output (where MR=MC). If AR > ATC, the firm earns supernormal profit, shown as a rectangle: (AR - ATC) × quantity. If AR < ATC, the firm makes a loss. If AR = ATC, the firm earns normal profit.

What is the shutdown condition in the short run?

In the short run, a firm should shut down if the price (or average revenue) falls below average variable cost (AVC). This is because the firm cannot cover its variable costs, so it is better to stop production and only pay fixed costs. If price is above AVC but below ATC, the firm continues operating because it contributes to fixed costs, reducing losses.

How do economies of scale affect long-run average costs?

Economies of scale cause long-run average costs (LRAC) to fall as output increases, due to factors like bulk buying, technical efficiencies, and managerial specialisation. This leads to a downward-sloping LRAC curve. If economies of scale persist over a large range of output, a natural monopoly may emerge. Diseconomies of scale, such as coordination problems, eventually cause LRAC to rise.

Why is MR = MC the profit-maximising rule?

If MR > MC, producing an extra unit adds more to revenue than to cost, so profit increases. If MR < MC, producing an extra unit adds more to cost than to revenue, so profit decreases. Therefore, profit is maximised where MR = MC, as any deviation reduces profit. This rule applies to all firms regardless of market structure.

Revenues, costs and profits

Q: What is the shutdown condition in the short run?

In the short run, a firm should shut down if the price (or average revenue) falls below average variable cost (AVC). This is because the firm cannot cover its variable costs, so it is better to stop production and only pay fixed costs. If price is above AVC but below ATC, the firm continues operating because it contributes to fixed costs, reducing losses.

Q: How do economies of scale affect long-run average costs?

Economies of scale cause long-run average costs (LRAC) to fall as output increases, due to factors like bulk buying, technical efficiencies, and managerial specialisation. This leads to a downward-sloping LRAC curve. If economies of scale persist over a large range of output, a natural monopoly may emerge. Diseconomies of scale, such as coordination problems, eventually cause LRAC to rise.

Q: Why is MR = MC the profit-maximising rule?

If MR > MC, producing an extra unit adds more to revenue than to cost, so profit increases. If MR < MC, producing an extra unit adds more to cost than to revenue, so profit decreases. Therefore, profit is maximised where MR = MC, as any deviation reduces profit. This rule applies to all firms regardless of market structure.

EDEXCEL

A-Level

This topic explores the relationship between a firm's revenue, costs, and profits. It covers the calculation and interpretation of revenue and cost concepts, the impact of diminishing marginal productivity on cost curves, economies and diseconomies of scale, and the conditions for profit maximisation and shut-down points.

Objectives

Exam Tips

Pitfalls

Key Terms

Mark Points

Topic Overview

Revenues, costs and profits form the bedrock of microeconomic analysis, enabling students to understand how firms make decisions and how markets function. Revenue is the income a firm receives from selling its output, costs are the expenses incurred in production, and profit is the difference between the two. This topic is central to Edexcel A-Level Economics because it links directly to market structures, business objectives, and the concept of efficiency. Mastering these concepts allows you to analyse real-world scenarios, such as why a firm might continue operating at a loss in the short run or how a monopoly can sustain supernormal profits.

The topic is divided into short-run and long-run analysis, with a focus on the distinction between fixed and variable costs, and the resulting shapes of cost curves. You will learn to calculate total, average, and marginal revenue and costs, and to identify profit-maximising output using the marginal revenue equals marginal cost (MR=MC) rule. Understanding these concepts is crucial for evaluating government policies, such as taxes or subsidies, and for assessing the impact of competition on firm behaviour. This knowledge also provides a foundation for more advanced topics like game theory and contestable markets.

In the wider Edexcel syllabus, revenues, costs and profits are essential for Theme 1 (Introduction to Markets and Market Failure) and Theme 3 (Business Behaviour and the Labour Market). They appear in multiple-choice questions, data response, and essay questions. A strong grasp of this topic will help you analyse case studies, draw and interpret diagrams, and evaluate the efficiency of different market structures. Ultimately, it equips you with the tools to think like an economist, weighing up the trade-offs firms face in pursuit of profit.

Key Concepts

Core ideas you must understand for this topic

→Total revenue (TR) = price × quantity; average revenue (AR) = TR/Q = price; marginal revenue (MR) = change in TR from selling one more unit. For a price-taking firm in perfect competition, AR = MR = price.
→Fixed costs (FC) do not vary with output (e.g., rent); variable costs (VC) change with output (e.g., raw materials). Total cost (TC) = FC + VC. Average fixed cost (AFC) falls as output rises, creating the U-shape of average total cost (ATC).
→Marginal cost (MC) is the change in total cost from producing one more unit. The MC curve intersects the ATC and AVC curves at their minimum points. Profit is maximised where MR = MC, provided price exceeds average variable cost in the short run.
→Normal profit is the minimum return needed to keep a firm in business (included as a cost); supernormal profit is profit above normal profit. In the short run, firms can earn supernormal or subnormal profits; in the long run, entry/exit erodes supernormal profits in perfect competition.
→Economies of scale cause long-run average costs to fall as output increases, leading to natural monopolies. Diseconomies of scale cause long-run average costs to rise, limiting firm size.

What You Need to Demonstrate

Key skills and knowledge for this topic

Calculation and understanding of total, average, and marginal revenue
Relationship between price elasticity of demand and total revenue
Calculation and understanding of total, fixed, variable, average, and marginal costs
Derivation of short-run cost curves from diminishing marginal productivity
Relationship between short-run and long-run average cost curves
Distinction between internal and external economies of scale
Identification of minimum efficient scale
Condition for profit maximisation (MC=MR)

Marking Points

Key points examiners look for in your answers

Calculation and understanding of total, average, and marginal revenue
Relationship between price elasticity of demand and total revenue
Calculation and understanding of total, fixed, variable, average, and marginal costs
Derivation of short-run cost curves from diminishing marginal productivity
Relationship between short-run and long-run average cost curves
Distinction between internal and external economies of scale
Identification of minimum efficient scale
Condition for profit maximisation (MC=MR)
Distinction between normal profit, supernormal profit, and losses
Analysis of short-run and long-run shut-down points

Examiner Tips

Expert advice for maximising your marks

💡Ensure all diagrams for costs and revenues are clearly labelled with axes and curves
💡Practice the calculation of revenue and cost metrics as these are frequently tested in data response questions
💡Be prepared to explain the difference between short-run and long-run cost structures
💡Use the MC=MR rule consistently when discussing profit maximisation
💡Always draw and label cost and revenue diagrams accurately. Use a ruler for straight lines, ensure curves are U-shaped, and clearly mark the profit-maximising output where MR=MC. Shade areas for profit or loss and label them correctly.
💡When evaluating, consider the assumptions behind the model. For example, in perfect competition, firms are price takers, but in reality, many firms have some market power. Discuss how this affects the shape of the revenue curves and profit outcomes.
💡Use real-world examples to illustrate your points. For instance, discuss how a supermarket might use loss leaders (selling below cost) to attract customers, or how a tech firm like Apple earns supernormal profit due to brand loyalty and economies of scale.

Common Mistakes

Pitfalls to avoid in your exam answers

Confusing average cost with marginal cost in diagrams
Failing to correctly identify the shut-down point in the short run versus the long run
Misinterpreting the relationship between PED and total revenue
Confusing internal economies of scale with external economies of scale
Misconception: 'Profit is maximised where total revenue is highest.' Correction: Profit is maximised where the difference between total revenue and total cost is greatest, which occurs where MR = MC, not where TR is highest. A firm can increase TR but if costs rise more, profit falls.
Misconception: 'Fixed costs affect marginal cost.' Correction: Fixed costs do not change with output, so they do not affect MC. MC depends only on variable costs. However, fixed costs do affect average total cost.
Misconception: 'A firm making a loss should always shut down.' Correction: In the short run, a firm should continue operating if price covers average variable cost (AVC), even if it is making a loss, because it contributes to fixed costs. Shutdown occurs only if price falls below AVC.

Frequently Asked Questions

Common questions students ask about this topic

Before You Start

Prior knowledge that will help with this topic

•Basic supply and demand analysis, including the concept of equilibrium price and quantity.
•Understanding of the production function and the law of diminishing returns, which explains the shape of short-run cost curves.
•Familiarity with the different market structures (perfect competition, monopoly, etc.) as context for revenue curves.

Key Terminology

Essential terms to know

Likely Command Words

How questions on this topic are typically asked

Calculate

Explain

Analyse

Evaluate

Distinguish

Ready to test yourself?

Practice questions tailored to this topic

Revenues, costs and profits

Topic Overview

Key Concepts

What You Need to Demonstrate

Marking Points

Examiner Tips

Common Mistakes

Frequently Asked Questions

Before You Start

Key Terminology

Likely Command Words

Ready to test yourself?

Related Topics in EDEXCEL A-Level Economics

Aggregate demand (AD)

Aggregate supply (AS)

Business growth

Business objectives

Topic Synopsis

Key Concepts & Core Principles

Exam Tips & Revision Strategies

Common Misconceptions & Mistakes to Avoid

Examiner Marking Points

Revenues, costs and profits

Topic Overview

Key Concepts

What You Need to Demonstrate

Marking Points

Examiner Tips

Common Mistakes

Frequently Asked Questions

What is the difference between normal profit and supernormal profit?

Why is the marginal cost curve U-shaped?

How do you calculate profit from a diagram?

What is the shutdown condition in the short run?

How do economies of scale affect long-run average costs?

Why is MR = MC the profit-maximising rule?

Before You Start

Key Terminology

Profit Maximisation vs Alternative Objectives

The Law of Diminishing Marginal Returns

Economies and Diseconomies of Scale

Likely Command Words

Ready to test yourself?

Related Topics in EDEXCEL A-Level Economics

Aggregate demand (AD)

Aggregate supply (AS)

Business growth

Business objectives