Difficulty: Introductory | Prerequisites: None (this is foundational material for the course)
Every manufacturing cost is either fixed, variable, or mixed, and understanding which is which determines how you build income statements and budget for production. Costs flow through raw materials, work in process, and finished goods before landing on the income statement as cost of goods sold. The two income statement formats (traditional and contribution) slice the same costs differently, and the difference matters for decision-making.
Fixed cost
A cost that remains constant in total regardless of changes in the level of activity within the relevant range. Think of it as the cost you pay whether the factory makes one unit or ten thousand.
Variable cost
A cost that changes in direct proportion to changes in the level of activity. In simple terms, the more you produce, the more you spend.
Mixed cost (semi-variable cost)
A cost that contains both a fixed component and a variable component, such as a salesperson's base salary plus commission. Think of it as a cost with a floor that rises as activity increases.
Step cost
A cost that stays flat over a range of activity, then jumps to a new level at a certain threshold. Over a short range it behaves like a variable cost; over a large range it looks fixed.
Relevant range
The band of activity within which the assumed cost behaviour (linear, fixed, or variable) actually holds. Outside this range the relationships break down.
Product cost (inventoriable cost)
A cost tied directly to manufacturing: direct materials, direct labour, and manufacturing overhead. These costs attach to inventory on the balance sheet until the goods are sold.
Period cost
A cost not directly involved in production, expensed in the period incurred rather than attached to inventory. Selling expenses and administrative expenses are the classic examples.
Direct materials
Raw materials that become an integral, traceable part of the finished product. In simple terms, the stuff you can point to in the final product.
Direct labour
Labour costs for workers who physically touch or directly transform the product during manufacturing.
Manufacturing overhead (MFG OH)
All manufacturing costs that are not direct materials or direct labour: indirect materials, indirect labour, factory rent, equipment depreciation, and so on.
Cost of goods manufactured (COGM)
The total production cost of goods completed during the period. It rolls out of work in process and into finished goods inventory.
Cost of goods sold (COGS)
The cost of the finished goods that were actually sold during the period. This is the number that hits the income statement.
Contribution margin
Sales revenue minus all variable expenses (including variable selling and administrative costs). It represents the amount available to cover fixed costs and generate profit.
Quality costs
Costs incurred to prevent, detect, and deal with defects. They fall into four categories: prevention, appraisal, internal failure, and external failure.
This is the foundation of the entire management accounting course. Before you can do CVP analysis, budgeting, variance analysis, or any costing method, you need to know how costs behave and how they flow through a manufacturing operation. Everything in Chapters 7 through 11 builds on these classifications. If you have not taken introductory financial accounting, the income statement mechanics here will be new; if you have, the key shift is learning to think about costs by behaviour (fixed vs. variable) rather than by function alone.
Fixed costs stay constant in total within the relevant range. Per-unit fixed cost falls as volume rises (spreading the cost over more units), but total fixed cost does not change.
Variable costs change in total in direct proportion to activity. Per-unit variable cost stays the same.
Mixed costs combine a fixed base with a variable component. A salesperson earning a base salary plus commission per sale is the textbook example.
Step costs are flat across a range, then jump. If the range is narrow the cost looks variable; if the range is wide it looks fixed.
Relevant range is the zone where these linear assumptions hold. Outside the relevant range, fixed costs may shift and variable cost per unit may change.
Prevention costs are spent to stop defects before they happen: quality training, process design, supplier certification.
Appraisal costs are inspection and testing costs incurred to catch defects before shipment.
Internal failure costs arise when defects are found before the product ships: rework, scrap, downtime.
External failure costs arise when defects reach the customer: warranty repairs, returns, reputation damage.
Product costs attach to inventory and become expenses only when the goods are sold. They include direct materials, direct labour, and manufacturing overhead. The VP of manufacturing's salary counts here because it relates to the production function.
Period costs are expensed in the period incurred, regardless of production. Selling expenses and general administrative expenses are period costs.
Traditional format
Sales minus COGS equals Gross Profit.
Gross Profit minus Selling Expenses minus Admin Expenses equals Net Income.
Contribution format
Sales minus all variable expenses (variable COGS plus variable selling and admin) equals Contribution Margin.
Contribution Margin minus all fixed expenses (fixed selling and admin) equals Net Income.
The contribution format groups costs by behaviour rather than function, which is essential for CVP analysis.
Contribution margin per unit tells you how much extra income each additional sale generates.
Costs move through three inventory accounts before reaching the income statement:
Raw materials: Beginning Raw Materials + Purchases minus Ending Raw Materials = Raw Materials Used in Production.
Direct materials consumed: The portion of raw materials used that is directly traceable to the product. (Total materials used minus indirect materials = direct materials.)
Total manufacturing cost: Direct Materials + Direct Labour + Manufacturing Overhead.
Cost of goods manufactured: Beginning WIP + Total Manufacturing Cost minus Ending WIP = COGM.
Cost of goods sold: Beginning Finished Goods + COGM minus Ending Finished Goods = COGS.
Net operating income: Gross Margin minus Selling Expenses minus Admin Expenses.
Indirect materials and indirect labour are part of manufacturing overhead, not direct cost categories.
\text{COGS} = \text{Beg Inv} + \text{Purchases} - \text{End Inv}\text{Gross Profit} = \text{Sales} - \text{COGS}\text{Net Income} = \text{Gross Profit} - \text{Selling Exp} - \text{Admin Exp}\text{Contribution Margin} = \text{Sales} - \text{All Variable Expenses}\text{Raw Materials Used} = \text{Beg RM} + \text{Purchased RM} - \text{End RM}\text{Total Manuf Cost} = \text{DM} + \text{DL} + \text{MFG OH}\text{COGM} = \text{Beg WIP} + \text{Total Manuf Cost} - \text{End WIP}\text{COGS} = \text{Beg FG} + \text{COGM} - \text{End FG}\text{Predetermined OH Rate} = \frac{\text{FC} + \text{Est. VC}}{\text{Direct Labour Hours}}\text{Direct Material} = \text{Total Material} - \text{Indirect Material}Understanding cost behaviour is how managers decide whether to accept a special order: if the price covers variable costs and contributes something toward fixed costs, the order adds profit, even if the price is below full cost per unit.
The flow-of-costs framework is exactly what ERP systems (SAP, Oracle) automate. Every time a factory issues raw materials to the production floor or transfers finished goods to the warehouse, the system is executing the journal entries behind these formulas.
Students often assume fixed costs are fixed per unit. They are not. Total fixed cost is constant; per-unit fixed cost drops as volume rises.
Students confuse manufacturing overhead with period costs. If it happens in the factory (indirect labour, factory utilities, equipment depreciation), it is product cost, not a period cost.
Students treat the VP of administration over manufacturing as a period cost. Because the role oversees the manufacturing function, the salary is a product cost.
Students forget that COGM and COGS are different numbers. COGM is what was completed; COGS is what was sold. They differ whenever finished goods inventory changes.
⚠️ Expect questions that give you partial inventory data and ask you to solve for COGM or COGS. Practise the six-step flow of costs until you can do it without notes.
⚠️ The contribution format income statement will reappear in every CVP and break-even question. Know how to reclassify costs by behaviour, not just by function.
⚠️ Quality cost classification (prevention vs. appraisal vs. internal failure vs. external failure) is a common multiple-choice target.
⚠️ Be ready to calculate direct materials from total materials minus indirect materials, and to identify which overhead items belong in product cost vs. period cost.
True or False: Total variable cost stays the same regardless of volume. (False: total variable cost changes with volume; per-unit variable cost stays the same.)
Fill in the blank: COGM = Beginning WIP + Total Manufacturing Cost minus ______. (Ending WIP)
True or False: A factory supervisor's salary is a period cost. (False: it is manufacturing overhead, a product cost.)
Fill in the blank: The four quality cost categories are prevention, appraisal, ______, and ______. (Internal failure, external failure)
True or False: Contribution margin equals Sales minus COGS. (False: Contribution margin equals Sales minus all variable expenses, including variable selling and admin.)
Q: A company has Beginning Raw Materials of $12,000, Purchases of $45,000, and Ending Raw Materials of $8,000. What is the Raw Materials Used in Production?
A: $12,000 + $45,000 minus $8,000 = $49,000.
Q: Direct Materials are $30,000, Direct Labour is $20,000, and Manufacturing Overhead is $15,000. Beginning WIP is $10,000 and Ending WIP is $5,000. What is Cost of Goods Manufactured?
A: Total Manufacturing Cost = $30,000 + $20,000 + $15,000 = $65,000. COGM = $10,000 + $65,000 minus $5,000 = $70,000.
Q: Classify the following cost: the salary of a quality inspector in the factory. Is it a product cost or a period cost?
A: Product cost. It is manufacturing overhead (indirect labour in the factory).
Q: A company reports Sales of $200,000, Variable COGS of $90,000, Variable Selling Expenses of $20,000, Fixed Manufacturing OH of $30,000, and Fixed Admin Expenses of $15,000. What is the Contribution Margin?
A: Contribution Margin = $200,000 minus $90,000 minus $20,000 = $90,000.
Q: A firm spends money on employee quality training. Which quality cost category does this fall under?
A: Prevention cost.
This material connects directly to CVP analysis (Ch. 1 continued), where the contribution margin becomes the central tool for break-even and profit planning. The distinction between fixed and variable costs is the entire foundation of the contribution format income statement used in CVP.
The flow-of-costs framework reappears in Activity-Based Costing (Ch. 7), where manufacturing overhead is allocated through activity cost pools instead of a single predetermined rate.
Absorption vs. variable costing (also Ch. 1) builds on whether fixed manufacturing overhead is treated as a product cost or a period cost, which directly depends on understanding the classifications covered here.
Fixed cost, variable cost, mixed cost, semi-variable cost, step cost, relevant range, linearity assumption, product cost, period cost, inventoriable cost, direct materials, direct labour, manufacturing overhead, indirect materials, indirect labour, COGS, COGM, cost of goods sold, cost of goods manufactured, work in process, WIP, finished goods, raw materials, contribution margin, contribution format income statement, traditional income statement, quality costs, prevention cost, appraisal cost, internal failure cost, external failure cost, gross profit, gross margin, net operating income, predetermined overhead rate, ACCT 3001, management accounting, managerial accounting, cost classification, cost behaviour