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Cost Classification and Cost Behaviour for ACCA BT

Updated 11 October 2026 · Fact-checked

Cost classification groups costs by function (production, administration, selling), by traceability (direct or indirect) and by behaviour (fixed, variable, semi-variable). To solve questions, decide what the cost is for, whether it traces to one cost unit, and whether it changes when activity changes within the relevant range.

Understand Cost Classification and Cost Behaviour

A business needs to know what its products and services cost. To do that it sorts costs into groups. Each grouping answers a different question.

Classification by function asks what the cost is for. Production costs are incurred making the product. Administration costs run the business. Selling and distribution costs win and deliver sales. Only production costs are included in the cost of inventory under IFRS.

Classification by element asks whether a cost can be traced to a cost unit (one unit of product or service). A direct cost can be traced to the cost unit economically, such as the wood in a table. An indirect cost (overhead) cannot, such as factory rent shared by all products. Direct materials, direct labour and direct expenses together make up prime cost.

Classification by behaviour asks what happens to total cost when activity changes. A variable cost changes in total in proportion to activity, but stays the same per unit. A fixed cost stays the same in total within a relevant range of activity, so cost per unit falls as output rises. A semi-variable (mixed) cost has a fixed part and a variable part, such as a phone bill with line rental plus a charge per call.

A step cost is fixed over a range of activity, then jumps to a higher level. Renting an extra warehouse once output passes a limit is an example. Fixed costs are only fixed within the relevant range and over a given time period. In the long run most costs can change.

Key formulas to remember

Prime cost: Prime cost = direct materials + direct labour + direct expenses; Total of all direct costs of a cost unit.
Total cost: Total cost = fixed costs + (variable cost per unit × activity level); Also written y = a + bx, where a is fixed cost and b is variable cost per unit.
Variable cost per unit: Variable cost per unit = total variable cost ÷ units; Constant per unit within the relevant range.
Fixed cost per unit: Fixed cost per unit = total fixed cost ÷ units; Falls as units rise, rises as units fall.
High-low method: Variable cost per unit = (cost at high activity − cost at low activity) ÷ (high activity − low activity); Then fixed cost = total cost at either level − (variable cost per unit × activity at that level). Use the highest and lowest activity levels.

How to solve Cost Classification and Cost Behaviour questions

Use this method for any classification or behaviour question. Decide one thing at a time.

1Read the question and identify the cost unit (product, service, department) and the activity measure (units, hours, miles).
2Ask what the cost is for: production, administration, or selling and distribution.
3Ask if the cost can be traced economically to the cost unit. If yes it is direct, if no it is indirect.
4Ask how total cost changes if activity rises. Proportional rise means variable. No change means fixed. Part fixed and part rising means semi-variable.
5Check for step costs and for the relevant range stated in the question.
6If numbers are given, split a semi-variable cost with the high-low method or use total cost = fixed + variable × units.
7Check your answer against the question wording, such as per unit or in total, before you select it.

Quickest way: Two-question test

When to use it: Use for multiple choice questions that ask you to classify a single cost under time pressure.

Question 1: Does this cost go into one unit of output directly? Yes means direct, no means indirect.
Question 2: If output doubled, would the total double (variable), stay put (fixed) or rise partly (semi-variable)?
For number questions, test with two activity levels: if total cost per unit is constant it is variable, if total cost is constant it is fixed.
Eliminate options that mix up total and per unit behaviour.

Common mistakes in Cost Classification and Cost Behaviour

Saying fixed cost per unit is constant.
The word fixed makes students apply it to every measure.
Fix: Fixed means total is fixed. Per unit it falls as output rises. Variable is the opposite: total rises, per unit is constant.
Treating all labour as direct and variable.
Students link labour with production without checking the details.
Fix: Only labour that makes the product and is traceable is direct. Supervisors are indirect. A salaried worker may be fixed, while piece-rate pay is variable.
Confusing direct/indirect with fixed/variable.
Both are common and the terms sound alike.
Fix: Direct/indirect is about traceability. Fixed/variable is about behaviour. A cost can be direct and fixed, such as a machine hired for one job.
Ignoring the relevant range and step costs.
Students memorise fixed as never changing.
Fix: Fixed costs hold only within a range of activity and period. Beyond it they step up.
Using the wrong data points in the high-low method.
Students pick the highest and lowest cost rather than activity.
Fix: Choose the highest and lowest activity levels and use their related costs.

Worked examples

Example 1

A company's maintenance cost was $14,000 at 2,000 machine hours and $20,000 at 5,000 machine hours. Assuming a semi-variable cost, what is the estimated cost at 3,500 machine hours?

Show the solution

Variable cost per hour = (20,000 − 14,000) ÷ (5,000 − 2,000) = 6,000 ÷ 3,000 = $2.
Fixed cost = 14,000 − (2,000 × 2) = 14,000 − 4,000 = $10,000.
Check at 5,000 hours: 10,000 + (5,000 × 2) = 20,000, which matches.
Cost at 3,500 hours = 10,000 + (3,500 × 2) = 10,000 + 7,000 = $17,000.

Answer: $17,000

Example 2

A furniture maker produces 4,000 chairs a year. Annual factory rent is $48,000 and wood costs $6 per chair. Output rises to 6,000 chairs within the relevant range. Find the rent per chair and the wood cost per chair at 6,000 chairs, and classify each cost by behaviour and traceability.

Show the solution

Rent per chair at 4,000 chairs = 48,000 ÷ 4,000 = $12.
At 6,000 chairs rent stays $48,000 in total, so rent per chair = 48,000 ÷ 6,000 = $8.
Wood per chair stays $6 because it is variable per unit. Total wood = 6,000 × 6 = $36,000.
Wood is a direct, variable cost: traceable to each chair and rises with output.
Factory rent is an indirect, fixed cost: shared by all chairs and unchanged in total.

Answer: Rent per chair falls from $12 to $8 and wood stays $6 per chair. Wood is direct and variable. Rent is indirect and fixed.

Exam tips

Always check whether the question asks about total cost or cost per unit. Examiners use this to set traps.
In multiple response questions, select exactly the stated number of options and test each against your two-question method.
Look for words like salaried, per unit, hired or rented. They signal behaviour.
For number entry questions, write down fixed and variable parts before calculating and give the answer in the stated units and rounding.
Expect scenario questions that mix function, traceability and behaviour. Classify on one basis at a time.

Practice questions from Financial information provided by business

Cost Classification and Cost Behaviour in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Cost Classification and Cost Behaviour: frequently asked questions

What is the difference between fixed and variable costs with examples?

A fixed cost stays the same in total as activity changes within the relevant range, such as factory rent or insurance. A variable cost changes in total in proportion to activity, such as raw materials or piece-rate wages. Variable cost per unit is constant, while fixed cost per unit falls as output rises.

What is the difference between direct and indirect costs?

A direct cost can be traced economically to a specific cost unit, such as fabric in a shirt. An indirect cost cannot, such as factory heating shared by many products. Indirect costs are also called overheads.

What is a semi-variable cost?

A semi-variable cost has a fixed part and a variable part. An example is a utility bill with a standing charge plus a charge per unit used. You can separate the parts with the high-low method.

Can a cost be both direct and fixed?

Yes. Directness is about traceability and fixedness is about behaviour. For example, hiring a special machine for a single contract at a set fee is direct to that contract and fixed in amount.