Understand the difference between variable costs, fixed costs and total…

The idea

Costs are the payments a business makes to produce and sell its output. Variable costs change directly with output: each extra unit made adds more cost, for example raw materials at £4 per unit, so 200 units cost £800 and 300 units cost £1,200. Fixed costs do not change with output over a period, such as rent of £2,000 per month, and are paid even at zero output. Total costs combine both: total costs = fixed costs + variable costs. At 200 units, total costs = £2,000 + £800 = £2,800; at 300 units, total costs = £2,000 + £1,200 = £3,200. The difference matters because variable costs rise as output rises, fixed costs stay constant in total, and total costs capture the full outlay. Understanding this helps a student judge break-even, pricing and profitability.

What earns the marks

• Defines variable costs as costs that vary directly with the level of output, giving a per-unit example such as materials or packaging.
• Defines fixed costs as costs that do not change with output in the short run, giving an example such as rent, insurance or salaries.
• States the relationship total costs = fixed costs + variable costs and applies it correctly to a numerical example.
• Explains that fixed costs are incurred even when output is zero, whereas variable costs are zero when nothing is produced.
• Uses a worked example to show how total costs change when output changes, for example comparing two output levels.
• Distinguishes total costs from average or unit costs, recognising that total costs are the whole outlay for a period.

Common mistakes and how to put them right

• Treating all costs as variable.

  Put it right: Fixed costs such as rent remain payable regardless of output.

• Adding fixed costs to variable costs but forgetting to multiply variable cost per unit by the number of units.

  Put it right: Calculate variable costs as unit cost × quantity first.

• Assuming fixed costs per unit stay constant.

  Put it right: Fixed costs per unit fall as output rises because the same total is spread over more units.

Exam tips

• Always label the cost type before calculating, so the examiner can see whether you are using a fixed or variable figure.
• Show the formula total costs = fixed costs + variable costs and substitute values line by line to secure method credit.
• Use a short context, such as a bakery, to make definitions concrete and to link costs to decisions about output.