What you'll learn
This revision guide covers all aspects of costs of production required for CIE IGCSE Economics. You will learn to distinguish between different types of costs, calculate average and marginal costs, and understand how these costs affect business decisions. These concepts are essential for analysing firm behaviour and appear regularly in both Paper 1 (multiple choice) and Paper 2 (structured questions).
Key terms and definitions
Fixed costs — costs that do not change with the level of output in the short run, such as rent, insurance premiums and salaries of permanent staff.
Variable costs — costs that change directly with the level of output, such as raw materials, packaging and piece-rate wages.
Total costs — the sum of all fixed costs and variable costs at any given level of output (TC = FC + VC).
Average cost — the cost per unit of output, calculated by dividing total costs by the quantity produced (AC = TC ÷ Q).
Marginal cost — the extra cost of producing one additional unit of output, calculated by the change in total cost divided by the change in quantity (MC = ΔTC ÷ ΔQ).
Short run — the time period in which at least one factor of production is fixed, meaning firms cannot change all their inputs.
Long run — the time period in which all factors of production are variable, allowing firms to change the scale of their operations.
Economies of scale — the cost advantages that firms experience when output increases in the long run, leading to falling average costs.
Core concepts
Fixed costs in detail
Fixed costs remain constant regardless of output levels. A Caribbean hotel pays the same annual property insurance whether it accommodates 1,000 guests or 10,000 guests per year. Similarly, a UK manufacturing firm pays the same factory rent whether production is high or low.
Common examples of fixed costs include:
- Rent and rates on premises
- Insurance premiums
- Salaries of permanent administrative staff
- Depreciation of machinery
- Marketing and advertising contracts
- Business rates and property taxes
Even if a firm temporarily stops production (producing zero output), fixed costs must still be paid. This explains why many businesses continue operating even when making losses in the short run — they need revenue to cover these unavoidable costs.
In the short run, fixed costs cannot be changed. However, in the long run, all costs become variable because firms can relocate to smaller premises, renegotiate contracts, or sell equipment.
Variable costs in detail
Variable costs rise and fall in direct proportion to output. If a Jamaican bakery doubles its bread production from 500 to 1,000 loaves daily, it will need approximately twice as much flour, yeast and electricity for ovens.
Typical variable costs include:
- Raw materials and components
- Packaging materials
- Energy and fuel used in production
- Piece-rate wages (payment per unit produced)
- Delivery and distribution costs
- Commission paid to sales staff
When output is zero, variable costs are also zero. This distinguishes them clearly from fixed costs. If a business temporarily closes, it avoids all variable costs but continues paying fixed costs.
The relationship between variable costs and output is not always perfectly proportional. Bulk-buying discounts may reduce the variable cost per unit as production increases. Conversely, paying overtime rates to workers might increase variable costs disproportionately at high output levels.
Total costs and their relationship
Total costs combine all expenditure required to produce a given output level. The formula is straightforward:
TC = FC + VC
At zero output, total costs equal fixed costs because variable costs are zero. As production increases, total costs rise due to increasing variable costs, while the fixed cost component remains constant.
For a UK coffee shop:
- Fixed costs (rent, insurance, manager's salary): £3,000 per month
- Variable costs per coffee (beans, milk, cup): £0.80
- If selling 2,000 coffees monthly: TC = £3,000 + (£0.80 × 2,000) = £4,600
- If selling 4,000 coffees monthly: TC = £3,000 + (£0.80 × 4,000) = £6,200
Understanding total costs is essential for calculating profit (revenue minus total costs) and making output decisions.
Average cost and its calculation
Average cost (also called average total cost) measures efficiency by showing the cost per unit. Lower average costs typically mean higher competitiveness as firms can either increase profit margins or reduce prices.
AC = TC ÷ Q or AC = (FC ÷ Q) + (VC ÷ Q)
Average cost typically falls as output increases from low levels. This occurs because fixed costs are spread over more units, reducing the fixed cost per unit. This is called spreading overhead costs.
At very high output levels, average costs may begin rising again due to problems managing large-scale operations, congestion in factories, or overtime payments. The output level with the lowest average cost is called the optimum output or minimum efficient scale.
Consider a Barbadian taxi firm:
- Fixed costs: $8,000 monthly (vehicle finance, licence)
- Variable cost per journey: $15 (fuel, driver payment)
| Output (journeys) | Total Cost | Average Cost |
|---|---|---|
| 100 | $9,500 | $95.00 |
| 200 | $11,000 | $55.00 |
| 400 | $14,000 | $35.00 |
| 800 | $20,000 | $25.00 |
Notice how average cost falls significantly as fixed costs are spread over more journeys.
Marginal cost and decision-making
Marginal cost is the additional cost incurred when producing one extra unit. This concept is crucial for business decisions about whether to expand or contract output.
MC = ΔTC ÷ ΔQ (change in total cost divided by change in quantity)
Because fixed costs don't change with output, marginal cost is determined entirely by variable costs. If producing one more unit adds £5 to variable costs, the marginal cost is £5.
Marginal cost typically decreases initially as workers become more efficient and equipment is used more productively. However, it eventually rises due to the law of diminishing returns — adding more variable factors (like workers) to fixed factors (like machinery) eventually yields smaller increases in output.
For a UK bicycle manufacturer:
- Producing the 100th bike increases total costs from £50,000 to £50,200
- MC = (£50,200 - £50,000) ÷ 1 = £200
If this bike sells for £250, the firm gains £50 additional profit from producing it. Rational firms continue production while marginal revenue exceeds marginal cost.
The relationship between different costs
Understanding how different costs interact is essential for exam success:
Average cost and marginal cost relationship:
- When MC < AC, average cost is falling
- When MC > AC, average cost is rising
- MC intersects AC at the lowest point of the average cost curve
This mirrors calculating your average test score. If your next test score (marginal) is below your current average, your average falls. If your next score exceeds your average, your average rises.
Short run versus long run: In the short run, some costs are fixed and cannot be adjusted. Firms can only vary output by changing variable inputs. In the long run, all costs become variable because firms can change factory size, relocate, or alter their scale completely.
This distinction matters for exam questions that ask about business responses to changing demand. Short-run responses are limited; long-run responses are more flexible.
Worked examples
Example 1: Calculating different types of costs
A Caribbean fruit juice company has the following cost structure:
- Fixed costs: $12,000 per month
- Variable cost per bottle: $2.50
Calculate the total costs, average cost and marginal cost when producing 4,000 bottles and 5,000 bottles monthly.
Solution:
At 4,000 bottles:
- TC = FC + VC = $12,000 + ($2.50 × 4,000) = $12,000 + $10,000 = $22,000
- AC = TC ÷ Q = $22,000 ÷ 4,000 = $5.50 per bottle
At 5,000 bottles:
- TC = $12,000 + ($2.50 × 5,000) = $12,000 + $12,500 = $24,500
- AC = $24,500 ÷ 5,000 = $4.90 per bottle
Marginal cost (producing the extra 1,000 bottles):
- MC = ΔTC ÷ ΔQ = ($24,500 - $22,000) ÷ (5,000 - 4,000) = $2,500 ÷ 1,000 = $2.50 per bottle
Mark scheme points: Correct formulas (1 mark each), accurate calculations (1 mark each), appropriate units shown (1 mark).
Example 2: Analysing cost data
Study the following data for a UK printing company:
| Output (units) | Total Cost (£) |
|---|---|
| 0 | 5,000 |
| 100 | 8,000 |
| 200 | 10,000 |
| 300 | 12,500 |
(a) Identify the fixed costs. [1 mark] (b) Calculate the variable costs of producing 200 units. [2 marks] (c) Calculate the average cost of producing 300 units. [2 marks] (d) Explain why average cost decreases as output rises from 100 to 200 units. [3 marks]
Solution:
(a) Fixed costs = £5,000 [When output is zero, only fixed costs remain]
(b) Variable costs at 200 units = Total costs - Fixed costs VC = £10,000 - £5,000 = £5,000
(c) Average cost at 300 units = TC ÷ Q AC = £12,500 ÷ 300 = £41.67 per unit
(d) Average cost decreases because fixed costs are spread over more units [1 mark]. At 100 units, AC = £80 per unit but at 200 units AC = £50 per unit [1 mark]. This demonstrates economies of scale as the fixed cost per unit falls from £50 (£5,000÷100) to £25 (£5,000÷200) [1 mark].
Example 3: Application to business decisions
A Trinidadian car wash business has fixed costs of $6,000 monthly and variable costs of $8 per car wash. The business charges $15 per car wash.
(a) Calculate how many car washes must be sold to break even. [3 marks] (b) Explain whether the business should accept a one-off order for 100 car washes at $10 each. [4 marks]
Solution:
(a) At break-even, Total Revenue = Total Costs Let Q = number of car washes 15Q = 6,000 + 8Q [1 mark] 7Q = 6,000 Q = 857.14, so 858 car washes [1 mark for calculation, 1 mark for rounding up]
(b) The marginal cost per car wash is $8 (the variable cost) [1 mark]. The special order offers $10 per wash, exceeding marginal cost by $2 [1 mark]. Therefore, each wash contributes $2 toward fixed costs and profit [1 mark]. The business should accept because it adds $200 total contribution toward covering fixed costs already incurred [1 mark].
Note: This assumes spare capacity exists and accepting won't displace regular customers.
Common mistakes and how to avoid them
Confusing fixed and variable costs: Remember fixed costs don't change with output. Salaries are only fixed if paid to permanent staff regardless of output; piece-rate wages are variable. Always ask: "Does this cost change if we produce one more unit?"
Forgetting that FC ≠ 0 when output is zero: Many students write that total costs are zero when output is zero. Fixed costs must still be paid even with zero production — this is why some firms continue operating at a loss short-term.
Miscalculating average cost: Don't divide fixed costs alone by quantity. Average cost requires total costs (fixed plus variable) divided by quantity. Double-check you've included both cost elements.
Assuming marginal cost equals average cost: These are different concepts. Marginal cost is the extra cost of one more unit; average cost is cost per unit for all units produced. Only at the minimum point of the average cost curve do they equal each other.
Ignoring units in calculations: Always include appropriate units (£, $, per unit, per month) in your answers. Exam mark schemes often allocate marks for correctly showing units, and omitting them suggests incomplete understanding.
Failing to link costs to business decisions: Don't just calculate costs — explain their significance. For example, explain that lower average costs improve competitiveness or that marginal cost below selling price justifies increased production.
Exam technique for "Firms: costs of production (fixed, variable, average and marginal)"
Command word awareness: "Calculate" requires showing your formula and working (2-3 marks typically). "Explain" needs reasoning with cause-and-effect linkages (3-4 marks). "Analyse" demands examining relationships and consequences (4-6 marks). "Discuss" requires balanced evaluation of different perspectives (6-8 marks).
Show your working clearly: Even if your final answer is incorrect, you can earn method marks by showing correct formulas and logical working. Write formulas first (e.g., AC = TC ÷ Q), then substitute numbers, then calculate. This structured approach maximizes marks.
Use cost data to support arguments: When questions ask about business decisions, reference specific cost figures from data provided. For example: "Average cost falls from £50 to £35 as output doubles, giving the firm a competitive advantage" scores higher than vague statements about "costs falling."
Draw and label diagrams when appropriate: Simple cost curves can earn marks and demonstrate understanding, particularly for "analyse" questions. Ensure axes are labelled (Cost on vertical axis, Output/Quantity on horizontal axis) and curves are clearly identified (AC, MC, TC).
Quick revision summary
Costs of production divide into fixed costs (unchanging with output like rent) and variable costs (changing with output like raw materials). Total costs combine both types. Average cost (TC÷Q) measures cost per unit and typically falls then rises as output increases. Marginal cost (ΔTC÷ΔQ) is the extra cost of producing one more unit, determined by variable costs only. Understanding these cost concepts helps firms make pricing, output and expansion decisions. In the short run some costs are fixed; in the long run all costs become variable.