Cost language and cost behaviour

Learning goals

• Classify costs by traceability, function, behaviour, and decision purpose.
• Compute direct materials, direct labour, manufacturing overhead, prime cost, and conversion cost.
• Explain total and per-unit behaviour within a relevant range.
• Distinguish product/inventoriable costs from period costs in a simple manufacturer.
• Recognize that one cost can have several valid classifications.

Prerequisite check

1. When does a manufacturer's product cost normally reach COGS?
2. Why might a cost be an asset for external reporting but still relevant to an internal decision now?

Vocabulary

• Cost object: item for which cost is measured, such as a product, job, service, department, or customer.
• Direct cost: economically traceable to a chosen cost object.
• Indirect cost: cannot be economically traced and is allocated using a rational basis.
• Direct materials (DM): traceable material becoming part of a product.
• Direct labour (DL): traceable production labour.
• Manufacturing overhead (MOH): production costs other than DM and DL.
• Product cost: manufacturing cost attached to inventory before sale in a simple absorption-costing model.
• Period cost: recognized in the period rather than inventoried in that model.
• Relevant range: activity band within which assumed cost behaviour is reasonable.

Core idea

Cost has no single permanent label. Ask cost for what purpose? Factory rent is indirect to one table, direct to the factory, fixed for a monthly volume range, product cost for external inventory, and possibly unavoidable for a short-term special-order decision.

Within a relevant range:

• Total variable cost changes in proportion to activity; variable cost per unit stays constant.
• Total fixed cost stays constant; fixed cost per unit changes inversely with volume.
• Mixed and step costs need more careful modelling.

Managerial reports are internal and not governed by IFRS/ASPE presentation in the same way as external statements. External inventory measurement still requires the applicable reporting framework.

Why this treatment makes sense

Different decisions need different views. Pricing a custom job needs traceable and capacity information; external inventory needs manufacturing cost under the framework; a shutdown decision needs avoidable future cash flows. Forcing one classification to answer every question produces bad decisions.

A repeatable method

Use OBJECT–FUNCTION–TRACE–BEHAVIOUR–PURPOSE:

1. Name the cost object.
2. Identify function: production, selling, administration, or other.
3. Decide whether tracing is economically feasible.
4. Describe total behaviour and relevant range; identify the activity driver.
5. Reclassify for the specific decision before calculating.

Worked example

Cedar Desk Co. makes 200 tables in a month, within its 100–300 table relevant range.

Manufacturing/product cost = $7,200 + $14,400 + $600 + $19,000 = $41,200, or $206 per table if all 200 are produced and the stated allocation is used.

Prime cost = DM $7,200 + DL $14,400 = $21,600. Conversion cost = DL $14,400 + MOH $19,600 = $34,000.

The $12,000 lease remains $12,000 at 150 or 250 tables, but per-unit allocation changes. At 350 tables, the company needs a second supervisor costing $3,000; the original fixed-cost model has crossed its relevant range.

Journal, ledger, and statement connection

In a manufacturer, qualifying DM, DL, and MOH flow through Raw Materials → Work in Process → Finished Goods → COGS. Selling commissions and office salary flow to period expense. This external-reporting flow is different from a contribution margin report, which groups variable and fixed costs for internal planning.

Common mistakes

• Calling every material direct; inexpensive glue may be impractical to trace.
• Treating direct and variable as synonyms. A dedicated machine lease can be direct but fixed.
• Dividing fixed cost by units and then assuming that per-unit figure stays fixed at a new volume.
• Including selling cost in manufacturing inventory without framework support.
• Double-counting DL in both prime and conversion cost when summing total manufacturing cost.
• Extending a linear estimate beyond capacity or the relevant range.
• Treating an allocated cost as automatically avoidable.

Guided practice

At 1,000 backpacks: fabric $18 each; sewing labour $12 each; factory power $2 each plus $1,500 monthly base; factory manager $5,000; machine depreciation $3,000; online ads $4,000; shipping to customers $6 each. Classify each by function and behaviour. Compute total manufacturing cost and per-unit product cost, treating all factory power as MOH and ads/shipping as period costs.

Independent practice

A bakery makes 4,000 frozen pies. Flour/fruit $4.50 per pie; production labour $2.25; packaging $0.50; factory sanitation $1,200 plus $0.20 per pie; factory rent $6,000; production equipment depreciation $1,500; salesperson salary $3,000 plus $0.30 per pie sold; head-office rent $2,200. All 4,000 are produced and 3,500 sold. Compute DM, DL, MOH, total manufacturing cost, unit product cost, ending Finished Goods cost, and period costs for the month. State two assumptions.

Self-check and solutions

Guided: Manufacturing: fabric $18,000; labour $12,000; power $3,500; manager $5,000; depreciation $3,000 = $41,500, or $41.50 each. Ads $4,000 and outbound shipping $6,000 are period costs under stated facts. Power is mixed; manager/depreciation fixed in range; fabric, labour, variable power, and shipping variable. Traceability depends on cost object and system.

Independent: DM includes ingredients $18,000 and packaging $2,000 = $20,000 under the packaging assumption. DL $9,000. MOH = sanitation $2,000 + rent $6,000 + depreciation $1,500 = $9,500. Manufacturing cost $38,500; unit cost $9.625. Ending 500 pies = $4,812.50. Period costs = salesperson $3,000 + 3,500($0.30) + head-office rent $2,200 = $6,250. Assumptions include units are equivalent/no spoilage or opening WIP, packaging is production cost, and fixed patterns hold in the relevant range.

Retrieval practice

1. Define a cost object and give three examples.
2. Contrast variable total/per-unit behaviour with fixed total/per-unit behaviour.
3. State the formulas for prime and conversion cost.
4. Give one cost with three different valid classifications.

Exam-style application

Factory fixed costs are $90,000 at 30,000 units, so an analyst predicts $3 per unit and $120,000 at 40,000 units. Diagnose the mistake. If 40,000 remains in the relevant range, state correct fixed total and per-unit cost.

Target: Fixed total remains $90,000; per-unit amount becomes $2.25. The analyst treated an allocated unit amount as a variable rate.

Lesson summary

Classify from a named cost object and decision. Behaviour assumptions apply only within a relevant range, and external product cost is not automatically the right cost for pricing, capacity, or short-term choices.