Process Costing and Joint Products

Introduction and context

Process costing is a method of assigning costs to large volumes of identical or similar units produced continuously through a sequence of processes. It is common in oil refining, chemicals, food processing, cement, textiles, paint, paper, beverages and utilities. Unlike job costing, which traces costs to separately identifiable jobs, process costing accumulates costs by department or process and then averages them over units produced.

Many production systems also involve material loss, partly completed units, transfers between departments, and the emergence of several products from one common input. These features create important measurement and control problems. A sound process-costing system must therefore answer four questions:

1. What quantity entered, was completed, was lost and remained in process?
2. What cost was incurred in each process?
3. How much cost belongs to completed output and closing work in progress?
4. Where a common production process produces several outputs, how should joint cost be assigned?

Process costing is not merely a bookkeeping technique. It provides information for cost control, valuation of inventory, pricing, production planning and performance evaluation.

Learning objectives

By the end of this chapter, you should be able to:

• distinguish process costing from job costing;
• prepare process accounts incorporating normal and abnormal losses;
• calculate equivalent units under weighted-average and, where relevant, FIFO approaches;
• value closing work in progress and transferred output;
• explain inter-process profits and their effect on inventory valuation;
• distinguish joint products, by-products and scrap;
• allocate joint costs using appropriate methods;
• evaluate the limitations and managerial consequences of joint-cost allocations.

1. Foundations of process costing

1.1 Characteristics

Process costing is appropriate when:

• production is continuous or repetitive;
• units are homogeneous or sufficiently similar;
• output passes through identifiable processes or departments;
• costs can be accumulated by process for a period; and
• individual units cannot be economically traced to particular batches or orders.

A process account normally records physical units on the debit side and completed output, losses and closing work in progress on the credit side. Costs charged include direct materials, direct labour and production overhead. In modern systems, direct labour and overhead are often combined as conversion costs.

1.2 Process costing compared with job costing

A process-costing system may still use standard costs, budgeted overhead rates and variance analysis. The method of cost accumulation does not determine whether costs are actual, normal or standard costs.

2. Physical flow and process-account logic

The basic physical-flow equation is:

All terms refer to the same period and process. If there is no opening work in progress, the equation simplifies accordingly. A cost reconciliation should also hold:

The precise presentation depends on the treatment of normal loss and scrap proceeds. Normal loss is expected under efficient operating conditions and is generally absorbed by good output. Abnormal loss and abnormal gain are treated separately so that inefficiency or unusually favourable performance is visible.

2.1 Normal loss

Normal loss is unavoidable loss expected from the nature of the process, such as evaporation, shrinkage or unavoidable residue. The expected quantity is usually calculated as a percentage of input, although the basis should reflect the production technology and contractual or engineering standards.

If normal loss has a realizable scrap value, the value of that scrap is normally credited to the process account. The cost of expected good output is therefore:

The cost per unit of good output, when there is no opening or closing work in progress, is:

This formula assumes that the normal-loss quantity and its scrap value are known and that all remaining units are good output.

2.2 Abnormal loss and abnormal gain

Abnormal loss is the actual loss exceeding normal loss. Abnormal gain occurs when actual loss is less than normal loss. Both are valued at the same average cost per equivalent good unit used for normal output, subject to the stage of completion and the cost convention adopted.

Abnormal loss should not be included in the cost of efficient production. It is transferred to an abnormal-loss account and ultimately charged to profit or loss, after any scrap proceeds. Abnormal gain is credited to profit or loss because it represents performance better than the normal expectation.

3. Equivalent units and work in progress

A partly completed unit does not represent one complete unit of work. Equivalent units convert incomplete physical units into the number of fully completed units represented by the work performed.

For a cost component such as materials or conversion, the general expression is:

This is applied separately to materials, labour and overhead whenever their completion percentages differ. For example, materials may be added at the beginning of a process while conversion occurs evenly throughout it.

3.1 Weighted-average method

The weighted-average method combines opening work-in-progress cost with current-period cost. It calculates a single average cost per equivalent unit:

The denominator includes all units completed during the period, whether they were started in the current period or carried in from opening work in progress, plus equivalent units in closing WIP. This method is practical and widely used, but it does not isolate current-period performance.

3.2 FIFO method

The FIFO method keeps opening WIP separate from work performed during the current period. Equivalent units for current-period work generally comprise:

FIFO is more informative when management wants to evaluate current-period efficiency, because opening WIP costs and prior-period work are excluded from current-period cost per equivalent unit. The method assumes that opening WIP is completed before units started during the period, or otherwise follows the chosen physical-flow convention.

3.3 Important assumptions

Equivalent-unit calculations require explicit assumptions:

• completion percentages must be based on physical production knowledge, not arbitrary estimates;
• materials and conversion may have different completion patterns;
• the same cost component should be measured consistently across opening WIP, completed output and closing WIP;
• losses must be incorporated at the stage at which they occur; and
• rounding should not create material differences in the cost reconciliation.

4. Worked example: normal loss, abnormal loss and closing WIP

Illustrative example. Process A receives 10,000 units. Normal loss is 5% of input and has scrap value of $1 per lost unit. Total process cost is $48,500. Actual output is 9,300 units, with no closing work in progress.

Normal loss is:

Expected good output is 9,500 units. Actual total loss is 700 units, so abnormal loss is 200 units:

The process account is credited with normal-loss scrap of $500:

The cost per good unit is:

The cost of abnormal loss is approximately:

The cost transferred for actual good output is:

Using exact arithmetic, $48,000 ÷ 9,500 × 9,300 = $46,989.47. The remaining amount, approximately $1,010.53, is the abnormal-loss valuation. Together they equal $48,000, the net process cost after the normal-loss scrap credit. The abnormal loss is reported separately rather than hidden in the cost of good output.

5. Worked example: equivalent units under weighted average

A process has the following data:

• Opening WIP: 1,000 units, 60% complete for conversion;
• units introduced during the period: 9,000;
• units completed and transferred: 8,000;
• closing WIP: 2,000 units, 50% complete for conversion;
• materials are added at the start of processing;
• opening WIP materials cost: $2,000;
• current materials cost: $18,000;
• opening conversion cost: $1,200;
• current conversion cost: $14,800.

There is no loss in this example. Physical units reconcile because 1,000 + 9,000 = 8,000 + 2,000.

Under weighted average, materials are 100% complete in both transferred units and closing WIP:

Conversion equivalent units are:

Costs per equivalent unit are:

Thus, completed output is valued at:

Closing WIP is valued at:

The small rounding difference is resolved by using unrounded unit costs in the accounting records. Total assigned cost is approximately $36,000, equal to total cost of $2,000 + $18,000 + $1,200 + $14,800.

6. Inter-process transfers and inter-process profits

In a multi-stage operation, output from one process becomes input to the next. Transfers may be made at cost or at a transfer price that includes a notional profit. A transfer price can support divisional performance evaluation and encourage responsibility for process efficiency, but it complicates inventory valuation.

Suppose Process 1 transfers output to Process 2 at cost plus 20%. If Process 1's cost is $100,000, the transfer price is:

The internal profit is $20,000. If Process 2 has not yet sold all its output externally at the reporting date, some of that profit remains unrealized from the perspective of the organisation as a whole. It must be eliminated from consolidated inventory and profit.

If closing inventory contains transfer-price cost of $30,000 and the transfer price represents cost plus 20% on cost, the profit loading is:

The denominator 120 reflects the transfer price index: cost is 100 and profit is 20. Alternatively, the loading rate on transfer price is 20/120. The adjustment reduces group inventory and profit by $5,000. The exact adjustment must distinguish opening unrealized profit, current transfers and external sales.

Inter-process profits should be governed by a documented policy. Transfer prices may be based on cost, market price, negotiated prices or dual pricing. A policy should balance controllability, motivation, tax and regulatory considerations, and faithful reporting.

7. Joint products and by-products

7.1 Meaning of joint production

Joint products are two or more products produced simultaneously from a common input up to a separation point, called the split-off point. Before that point, costs cannot normally be traced economically to individual products. Costs incurred before separation are joint costs; costs incurred after separation are separable costs.

Examples include:

• crude oil refined into petrol, diesel and lubricants;
• milk processed into cream, butter and skimmed milk;
• livestock processed into meat, hides and other outputs; and
• timber converted into different grades and products.

A by-product is an output of relatively minor sales value compared with the main products. The distinction is partly relative and may change with technology and market conditions. Scrap is generally a residual with little value and may be treated as a reduction of process cost or other income according to policy.

7.2 The split-off point

The split-off point is the stage at which products become separately identifiable. Joint costs incurred before this point cannot be assigned using a physical causal relationship without adopting an allocation convention. Costs after split-off are separable and should normally be traced directly to the relevant product.

A crucial managerial principle follows: joint costs are sunk with respect to decisions made after split-off. The decision to process a product further should be based on incremental revenue and incremental separable cost, not on an allocated share of unavoidable joint cost.

8. Methods of allocating joint costs

8.1 Physical-units method

Joint cost is allocated in proportion to output quantity, weight, volume or another physical measure:

This method is simple and objective where products are measured in comparable units. It is inappropriate when physical units have little relationship to selling value or economic benefits.

8.2 Relative sales-value-at-split-off method

When products have observable selling prices at split-off:

This method allocates cost according to relative market value and is often persuasive for financial reporting. It requires reliable prices at the split-off point.

8.3 Net realisable value method

If products cannot be sold at split-off, estimated net realisable value (NRV) is used:

Joint cost is allocated as:

NRV depends on estimates of future prices and costs, so sensitivity analysis and regular review are important.

8.4 Constant gross-margin percentage method

This method allocates joint cost so that every product has the same gross-margin percentage on sales. It is more complex and may be useful when management seeks a consistent margin convention, but it is highly dependent on the chosen sales and cost data.

8.5 Comparison of methods

No allocation method proves that a product caused its assigned share of joint cost. Allocation is a measurement convention for inventory, product profitability and reporting. For decisions, incremental cash flows are usually more relevant.

9. Worked example: joint-cost allocation and further processing

A company incurs joint cost of $120,000 and obtains three products at split-off:

Sales values at split-off are:

• A: 4,000 × $12 = $48,000;
• B: 3,000 × $20 = $60,000;
• C: 5,000 × $6 = $30,000.

Total split-off sales value is $138,000. Under the relative-sales-value method, joint cost allocations are:

• A: $120,000 × $48,000 ÷ $138,000 = $41,739 approximately;
• B: $120,000 × $60,000 ÷ $138,000 = $52,174 approximately;
• C: $120,000 × $30,000 ÷ $138,000 = $26,087 approximately.

The allocations sum to $120,000, subject to rounding.

The further-processing decision is independent of these allocations. Incremental benefit from further processing is:

• A: additional revenue of 4,000 × ($15 − $12) = $12,000; less $8,000 separable cost = $4,000 benefit;
• B: 3,000 × ($24 − $20) = $12,000; less $5,000 = $7,000 benefit;
• C: 5,000 × ($7 − $6) = $5,000; less $10,000 = $5,000 loss.

Therefore A and B should be processed further, assuming capacity, quality, risk and demand constraints do not alter the analysis. C should be sold at split-off. Allocated joint cost is irrelevant to this incremental decision.

10. By-products and accounting treatment

By-products may be accounted for in several ways, subject to applicable financial-reporting standards and consistent policy:

1. Other-income method: proceeds from sale are reported as other income when realised.
2. Cost-reduction method: the expected net realisable value of the by-product reduces the main process cost.
3. Separate-product method: the by-product receives an allocated cost and is treated like a product when its value is material.
4. Credit at selling value less further cost: estimated net proceeds are credited to the main process account.

The selected method should reflect materiality, consistency and the economic substance of the output. A material by-product should not be hidden in a miscellaneous account merely to simplify bookkeeping.

11. Case study: Riverbend Oils Ltd. (illustrative)

Background

Riverbend Oils Ltd. refines crude oil continuously. The refining process produces petrol, diesel and residual fuel at a common split-off stage. Petrol and diesel are further blended, while residual fuel can be sold immediately. Evaporation and sludge create normal process loss.

Problem

Management used physical litres to allocate all joint costs. Diesel appeared unprofitable, although its selling price and contribution after split-off were strong. In addition, Process 2 transferred blended products to the packaging department at cost plus 15%, and closing inventory included substantial internal profit.

Analysis

The finance team first prepared a physical reconciliation for crude input, normal loss, transfers and closing WIP. Equivalent units were calculated separately because materials entered at the beginning of blending but conversion occurred throughout the process. Normal loss was absorbed by good output, while an unusual shutdown loss was reported as abnormal loss.

For joint products, management compared physical-unit allocations with relative sales values at split-off. The latter better reflected economic value because one litre of petrol was not economically equivalent to one litre of residual fuel. Separable blending and packaging costs were traced directly to the relevant product.

The team then evaluated further processing using incremental revenue less separable cost. It did not use the allocated share of crude-oil joint cost in that decision. Finally, it calculated the unrealized profit included in closing inventory from the 15% inter-process markup and eliminated it for group reporting.

Approach and outcome

The company adopted the following policy:

• weighted-average equivalent units for monthly external reporting;
• FIFO analysis for operational performance reviews;
• sales value at split-off for joint-cost allocation where reliable prices existed;
• direct tracing of separable costs;
• abnormal losses reported separately;
• elimination of unrealized inter-process profit in consolidated accounts; and
• monthly review of normal-loss standards using engineering and production data.

Reported product margins became more credible, diesel was retained as a priority product, and a recurring packaging bottleneck was identified. The change did not alter total joint cost; it improved classification, control and decision quality.

Learning points

• Physical flow must be reconciled before costs are assigned.
• A product can appear unprofitable solely because of an arbitrary allocation.
• Joint-cost allocation for reporting is different from incremental analysis for decisions.
• Inter-process profit can overstate group inventory and profit.
• Production, engineering, sales and finance must collaborate when setting loss standards and completion percentages.

12. Controls, technology and professional practice

Modern enterprise-resource-planning systems can capture quantities, batch movements, process stages, scrap, quality grades and completion estimates. Sensors and production execution systems may provide timely data for yield and loss analysis. Artificial intelligence can assist in forecasting yields or detecting unusual loss patterns, but it should not replace engineering validation or accounting judgement.

Important controls include:

• independent approval of normal-loss standards;
• reconciliations of input, output, loss and WIP;
• documented completion percentages;
• review of unusual variances and abnormal losses;
• physical verification of inventory;
• consistent joint-cost allocation policies;
• elimination schedules for unrealized inter-process profit; and
• audit trails for estimates, overrides and system changes.

Ethically, managers should not manipulate completion percentages or normal-loss standards to shift costs between periods, inflate inventory or meet performance targets. Product costs should be presented transparently, with assumptions disclosed where estimates materially affect reported results. The applicable financial-reporting framework, tax rules and industry regulation must be consulted because treatment of inventory, by-products and internal transfers can differ across jurisdictions.

13. Limitations and critical evaluation

Process costing produces useful averages, but averages can conceal variation in product quality, machine efficiency and batch complexity. Equivalent units depend on estimates, especially when conversion is not uniform. Normal-loss percentages may become outdated as equipment, raw materials or operating conditions change.

Joint-cost allocations are inherently conventional before split-off. They can support inventory valuation and segment reporting, but they should not be interpreted as precise causal measures of product profitability. A product manager evaluated solely on allocated joint costs may make dysfunctional decisions, such as discontinuing a product that provides a positive contribution after avoidable costs.

A robust system therefore combines process costing with operational measures such as yield, first-pass quality, downtime, throughput, energy consumption, waste rate and contribution margin. Financial and non-financial measures should be interpreted together.

Chapter Summary

Process costing accumulates costs by process and assigns average costs to homogeneous output. Physical-flow reconciliation is the foundation of reliable process accounts. Normal loss is expected and generally absorbed by good output, with scrap proceeds reducing process cost. Abnormal loss and abnormal gain are reported separately to reveal departures from expected performance.

Equivalent units convert partly completed production into completed-unit equivalents. Weighted average combines opening and current-period costs, while FIFO isolates current-period work and is useful for performance analysis. Different completion percentages must be applied to materials and conversion costs where their production patterns differ.

Inter-process transfers may occur at cost or at a markup. Internal profit in unsold downstream inventory is unrealized from the viewpoint of the organisation as a whole and must be eliminated for consolidated reporting. Joint products arise from a common process up to split-off; by-products have relatively minor value. Joint costs may be allocated using physical units, sales value at split-off, NRV or constant gross margin, but allocations are conventions rather than causal facts. Further-processing decisions should use incremental revenue and separable cost, not allocated joint cost.

Effective practice requires accurate production data, documented assumptions, strong reconciliations, ethical reporting and cooperation among accounting, engineering, production and sales personnel.

Key Terms

Process costing: A system that accumulates and assigns costs by process or department for homogeneous output.

Process account: An account recording units and costs entering, leaving and remaining in a process.

Normal loss: Expected unavoidable loss under efficient operating conditions.

Abnormal loss: Loss exceeding the expected normal quantity.

Abnormal gain: Actual loss below the expected normal quantity.

Scrap value: Proceeds obtainable from disposing of a lost or residual material.

Work in progress (WIP): Units started but not fully completed at a reporting date.

Equivalent unit: A completed-unit measure of partly completed production.

Conversion cost: Direct labour and production overhead used to convert materials into output.

Weighted-average method: An equivalent-unit method combining opening WIP and current-period costs.

FIFO method: A method separating prior-period WIP work from current-period work.

Inter-process transfer: Movement of output from one process to another.

Inter-process profit: Markup included in an internal transfer price.

Joint product: A significant product arising with other products from common input before split-off.

Joint cost: Cost incurred before joint products become separately identifiable.

Split-off point: The stage at which joint products become separately identifiable.

Separable cost: Cost incurred after split-off that can be traced to a particular product.

By-product: A secondary output with relatively minor value compared with main products.

Net realisable value: Final sales value less separable processing and selling costs.

Review Questions

5 Short Answer Questions

1. What production conditions make process costing appropriate?
2. Distinguish normal loss from abnormal loss.
3. Why are equivalent units calculated separately for materials and conversion costs?
4. What is the split-off point in joint production?
5. Why must unrealized inter-process profit be eliminated from group inventory?

5 Long Answer Questions

1. Explain the preparation and interpretation of a process account containing normal loss, abnormal loss and scrap proceeds.
2. Compare the weighted-average and FIFO methods of equivalent-unit costing, including their managerial uses.
3. Explain four methods of allocating joint costs and evaluate their advantages and limitations.
4. Discuss the accounting and decision-making implications of inter-process profit.
5. Explain the distinction between joint products, by-products and scrap, and describe appropriate accounting treatments.

3 Analytical / Application Questions

1. A process receives 20,000 units, has normal loss of 4%, actual loss of 1,000 units and process cost of $95,000. Normal-loss scrap is $0.50 per unit. Calculate abnormal loss and the cost per good unit, assuming no WIP.
2. A company allocates all refinery joint costs using litres. Critically assess whether this is suitable when product selling prices differ substantially, and recommend an alternative method.
3. A product can be sold at split-off for $18 per unit or processed further and sold for $25. Further processing costs $5 per unit. Should it be processed further? Explain why the allocated joint cost should not affect the decision.

Multiple Choice Questions with Answers

Question 1

Which condition most strongly supports the use of process costing?

A. Each customer orders a uniquely designed product

B. Output is homogeneous and produced continuously

C. Each job uses separately traceable materials

D. Production is limited to one custom contract

Correct Answer: B. Output is homogeneous and produced continuously

Question 2

Normal loss is generally treated as:

A. A separate operating asset

B. A cost absorbed by expected good output

C. A prior-period error

D. A gain transferred to retained earnings

Correct Answer: B. A cost absorbed by expected good output

Question 3

A process receives 10,000 units and normal loss is 5%. Expected good output is:

A. 500 units

B. 5,000 units

C. 9,500 units

D. 10,500 units

Correct Answer: C. 9,500 units

Question 4

Under the weighted-average method, the cost per equivalent unit normally includes:

A. Only current-period costs

B. Only opening WIP costs

C. Opening WIP cost plus current-period cost

D. Only abnormal-loss cost

Correct Answer: C. Opening WIP cost plus current-period cost

Question 5

If materials are added at the beginning and closing WIP contains 2,000 units, materials equivalent units for those units are usually:

A. 0

B. 500

C. 1,000

D. 2,000

Correct Answer: D. 2,000

Question 6

Which item is a cost incurred after the split-off point for a specific product?

A. Joint crude-oil refining cost

B. Common extraction cost before identification

C. Product-specific packaging cost

D. Common raw-material cost

Correct Answer: C. Product-specific packaging cost

Question 7

A by-product is generally:

A. An output of relatively minor value compared with main products

B. A product that never has a selling price

C. A normal loss with no recovery value

D. An abnormal gain from efficient production

Correct Answer: A. An output of relatively minor value compared with main products

Question 8

If a transfer price is cost plus 20%, the profit loading contained in a transfer-price inventory value of $120,000 is:

A. $20,000

B. $24,000

C. $100,000

D. $12,000

Correct Answer: A. $20,000

Question 9

For a further-processing decision after split-off, the most relevant comparison is:

A. Allocated joint cost versus total sales value

B. Incremental revenue versus separable processing cost

C. Opening WIP cost versus closing WIP cost

D. Normal loss versus abnormal gain

Correct Answer: B. Incremental revenue versus separable processing cost

Question 10

Under the NRV method, product NRV is calculated as:

A. Final sales value plus joint cost

B. Final sales value minus separable processing and selling costs

C. Joint cost minus final sales value

D. Physical units divided by total units

Correct Answer: B. Final sales value minus separable processing and selling costs