Cost and Management Accounting · Cost Sheet

Cost Concepts and Cost Classification for CA Inter Costing

Updated 4 October 2026 · Fact-checked

Cost is the amount of resources sacrificed to get a product or service. Classification groups costs by nature (material, labour, expenses), function, behaviour (fixed, variable, semi-variable) and traceability (direct, indirect). To solve questions, identify the basis first, then test each cost against that basis.

Understand Cost Concepts and Cost Classification

Cost is the value of resources given up to make a product or provide a service. In cost accounting, you also ask: cost of what, and for which period? That 'what' is the cost object.

A cost unit is the unit of product or service for which you measure and state cost. Examples: a tonne of steel, a metre of cloth, a passenger-km for transport, a bed-day for a hospital. A cost centre is a location, person or item of equipment (or a group of these) for which costs are collected. Examples: a machine shop, the stores department, a canteen. In short, the cost unit is what you cost; the cost centre is where you collect cost.

Costs can be classified in many ways, and each way answers a different question. By nature: material, labour, expenses. By function: production, administration, selling and distribution, research and development. By behaviour: how cost changes when activity changes. By traceability: whether cost can be linked to one cost unit economically.

Behaviour needs care. A variable cost changes in total in proportion to activity, but stays constant per unit. A fixed cost stays constant in total within the relevant range and the period, but falls per unit as output rises. A semi-variable cost has a fixed part and a variable part, for example an electricity bill with a fixed charge plus a per-unit charge. A step cost stays fixed over a range and jumps at a threshold, for example a supervisor needed for every 50 workers.

Traceability: a direct cost can be identified with a cost unit in an economically feasible way (wood in a table). An indirect cost (overhead) cannot, or is not worth tracing (factory rent, lubricants). The same cost can be direct for one cost object and indirect for another. A factory manager's salary is indirect to a product but direct to the factory as a cost centre.

Key rules to remember

Prime cost: Prime cost = Direct material + Direct labour + Direct expenses; All direct costs. Overheads are not part of it.
Cost per unit (variable): Variable cost per unit = Total variable cost ÷ Units of activity; Stays constant per unit within the relevant range.
Fixed cost per unit: Fixed cost per unit = Total fixed cost ÷ Units of activity; Falls as activity rises; total stays constant.
Semi-variable cost: Total cost = Fixed element + (Variable rate × Activity); Use two activity levels to split: variable rate = change in cost ÷ change in activity.
Classification by function: Production, Administration, Selling & Distribution, R&D; Production cost is usually treated as product cost; the others as period-wise overheads in the cost sheet.

How to solve Cost Concepts and Cost Classification questions

Use this method for any question that asks you to classify, identify or explain costs.

1Read the question and note the basis of classification asked: nature, function, behaviour or traceability. Also note the cost object (product, department, job).
2List each cost item given in the question.
3Test each item against the basis. For traceability ask: can it be economically traced to one unit? For behaviour ask: what happens in total if output doubles?
4Check the cost object. A cost may be direct for a department but indirect for a product.
5For semi-variable items, split into fixed and variable using the high-low method or the data given.
6Write the answer in a small table-like list: item, class, one-line reason.
7Give definitions only where asked, in one or two sentences, with an example.

Quickest way: Basis-first classification with one-line reasons

When to use it: Use it for MCQs and short written classification questions under time pressure.

MCQ: identify the basis in the stem, then eliminate options that use a different basis (for example, 'selling cost' is functional, not behavioural).
Remember the pairs: fixed total constant but unit cost falls; variable total rises but unit cost constant.
If an item has both a fixed charge and a usage charge, it is semi-variable.
Written: for every item write 'Item - Class - Reason' in one line. Step marks come from the reason.
Always name the cost object in your answer, such as 'direct for the product'.

Common mistakes in Cost Concepts and Cost Classification

Saying fixed cost per unit is constant and variable cost per unit changes.
Students mix up total cost and per-unit cost.
Fix: Fixed: total constant, per unit falls. Variable: total rises, per unit constant. Say 'total' or 'per unit' every time.
Treating all factory costs as indirect and all administration costs as direct.
Function and traceability get confused.
Fix: Function tells where a cost arises. Traceability tells if it links to the cost unit. A machine operator's wages are a factory cost and also direct.
Confusing cost unit with cost centre.
Both sound like 'something you cost'.
Fix: Cost unit is the unit of output you measure (tonne, bed-day). Cost centre is where costs are collected (department, machine).
Classifying a cost as direct or indirect without naming the cost object.
The same cost can change class with the object.
Fix: State the object in your answer, for example 'indirect for the product, direct for the department'.
Calling a step cost or semi-variable cost purely fixed.
Students focus on the fixed part.
Fix: If cost moves with activity in any way, check for a variable element or a step. Classify as semi-variable or step.
Listing prime cost with overheads included.
Students include factory overheads while adding up direct costs.
Fix: Prime cost has only direct material, direct labour and direct expenses.

Worked examples

Example 1

A furniture factory incurs these costs: (a) timber used in tables, (b) wages of carpenters working on tables, (c) factory rent, (d) commission to salesmen, (e) electricity bill with a fixed monthly charge of ₹4,000 plus ₹5 per unit consumed. Classify each by traceability, function and behaviour as far as applicable, with the product 'table' as the cost unit.

Show the solution

(a) Timber: traceable to each table, so direct; it is a material cost; production function; variable with output.
(b) Carpenters' wages: traceable to tables, so direct labour; production function; generally variable if paid per piece or time worked on output.
(c) Factory rent: cannot be economically traced to one table, so indirect; production overhead; fixed.
(d) Salesmen's commission: not traced to the making of a table; selling and distribution overhead; indirect to the product's production; variable with sales.
(e) Electricity: fixed charge plus usage charge, so semi-variable; indirect, as it is not traced to a single table; production overhead if used in the factory.

Answer: Timber and carpenters' wages are direct; rent, commission and electricity are indirect. Behaviour: timber variable, wages variable, rent fixed, commission variable, electricity semi-variable.

Example 2

The power cost of a plant was ₹36,000 at 4,000 machine hours and ₹48,000 at 6,000 machine hours. Treating it as semi-variable, find the fixed element and variable rate, and the cost at 5,000 hours.

Show the solution

Change in cost = 48,000 − 36,000 = ₹12,000.
Change in activity = 6,000 − 4,000 = 2,000 hours.
Variable rate = 12,000 ÷ 2,000 = ₹6 per hour.
Variable cost at 4,000 hours = 4,000 × 6 = ₹24,000.
Fixed element = 36,000 − 24,000 = ₹12,000.
Check at 6,000 hours: 12,000 + (6,000 × 6) = 12,000 + 36,000 = ₹48,000, which matches.
Cost at 5,000 hours = 12,000 + (5,000 × 6) = 12,000 + 30,000 = ₹42,000.

Answer: Fixed element ₹12,000; variable rate ₹6 per machine hour; cost at 5,000 hours ₹42,000.

Exam tips

Read the basis of classification in the stem first. Many MCQs give a correct statement under a wrong basis.
In descriptive answers, write item, class and reason. A reason earns the step mark even if the class is debatable.
For behaviour questions, mention the relevant range and the period. Fixed costs are fixed only within these limits.
Practise the high-low split. It is a frequent small numerical in this topic.
Learn one example for each term: cost unit, cost centre, step cost, semi-variable cost. Examiners often ask for examples.

Practice questions from Cost Sheet

Cost Concepts and Cost Classification in other exams

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

Cost Concepts and Cost Classification: frequently asked questions

What is the difference between direct and indirect cost?

A direct cost can be economically traced to a specific cost unit, such as timber in a table. An indirect cost cannot be traced that way, such as factory rent, and is shared through apportionment and absorption.

What is the difference between a cost unit and a cost centre?

A cost unit is the unit of product or service whose cost you measure, such as a tonne or a bed-day. A cost centre is a location, person or equipment for which you collect costs, such as a machining department.

Give examples of fixed, variable and semi-variable costs.

Fixed: factory rent or insurance premium. Variable: direct material or piece-rate wages. Semi-variable: an electricity bill or telephone bill with a fixed charge plus a usage charge.

Does fixed cost per unit change?

Yes. Total fixed cost stays constant within the relevant range, but fixed cost per unit falls as output rises and rises as output falls.