Introduction to Cost Accounting
AdvancedCost accounting classifies costs as direct or indirect, fixed or variable to support management decisions; cost-volume-profit analysis uses contribution to find the break-even point and target-profit volume, while sunk and opportunity costs sharpen pricing and order decisions.
- Cost accounting serves internal decisions: pricing, cost control and option appraisal
- Direct versus indirect is about traceability; fixed versus variable is about cost behaviour
- Contribution = sales revenue − variable costs; it absorbs fixed costs first, and the remainder is profit
文體小知識：商業知識說明文——講解成本的分類方法與本量利分析，示範保本點的計算，並說明成本概念如何支援商業決策。
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1Financial accounting looks backward, preparing statements mainly for external users; cost accounting looks inward, breaking down production and operating costs so that management can set prices, control spending and appraise options. Whether a business makes money often depends on how precisely it knows its costs — cost accounting turns costs into decision information.
2Costs can be classified in several ways. By traceability: direct costs can be traced to a specific product, such as flour and the baker's wages in bread-making; indirect costs (overheads) cannot be traced directly, such as oven electricity and factory rent. By behaviour: fixed costs stay constant in total over a period regardless of output, like monthly rent; variable costs move in proportion to output, like packaging materials.
3Cost-volume-profit (CVP) analysis studies how costs, prices and volume shape profit, resting on the idea of contribution: for each unit sold, selling price minus unit variable cost is the unit contribution, which first absorbs fixed costs — anything left is profit. Break-even volume = fixed costs ÷ unit contribution: the output at which contribution exactly offsets fixed costs and profit is zero.
4Target profit can be worked backwards: required volume = (fixed costs + target profit) ÷ unit contribution. For example, with monthly fixed costs of $45,000 and unit contribution of $15, break-even is 3,000 units; to earn $15,000 a month, 4,000 units are needed. CVP analysis also estimates how price cuts or rent rises will shift profit — how many extra units must be sold to make up the difference.
5Decisions require separating relevant from irrelevant costs. Sunk costs are already paid and unrecoverable — no decision can change them, so ignore them firmly. Opportunity cost is the return forgone from the best alternative and must count. Take a special order: with spare capacity, as long as the price exceeds unit variable cost and covers any related costs, accepting it adds to total profit.
1Summary 重點摘要
Cost accounting classifies costs as direct or indirect, fixed or variable to support management decisions; cost-volume-profit analysis uses contribution to find the break-even point and target-profit volume, while sunk and opportunity costs sharpen pricing and order decisions.
2Vocabulary cards Vocabulary
The branch of accounting that classifies, records and analyses costs to inform pricing and decisions.
A cost traceable directly to a product or department, such as direct materials and direct labour.
Also overheads: costs that cannot be traced directly to individual products, such as factory rent and machine depreciation.
A cost whose total stays constant within the relevant range, such as monthly rent and supervisors' salaries.
A cost whose total moves in proportion to output, such as raw materials and piece-rate wages.
Sales revenue minus variable costs; contribution absorbs fixed costs, and whatever remains is profit.
The technique analysing how changes in cost, price and volume affect profit, yielding break-even and target-profit volumes.
The volume or sales value at which contribution exactly covers fixed costs and profit is zero.
A cost already paid and unrecoverable; irrelevant to future decisions and to be ignored.
The return forgone from the best alternative when a choice is made — a relevant cost for decisions.
3Step by step Steps
- Step 1: The role of cost accountingFinancial and cost accounting serve different masters: the former reports the past to external users such as shareholders and lenders; the latter equips management with information for pricing, cost control and option appraisal. For example, a bakery knows each cake uses $3 of ingredients, but to set a price it must also know how electricity and rent are spread, and how a price cut would affect profit — precisely the province of cost accounting. The more accurate the cost information, the sounder the business decision.
- Step 2: Direct and indirect costsClassified by traceability: costs traceable to a product are direct costs — direct materials and direct labour; those not directly traceable and needing allocation on a fair basis are indirect costs, also called overheads. For example, in a furniture factory the timber and the carpenter's wages for one dining table are direct costs; factory rent, saw depreciation and electricity are indirect, because they serve all products at once and cannot be pinned to any single table.
- Step 3: Fixed and variable costsClassified by behaviour: totals unaffected by output are fixed costs; totals moving in proportion to output are variable costs. For example, a print shop pays $8,000 rent monthly even with no orders — fixed; paper and ink rise and fall with volume — variable. Note that fixed costs are fixed only within the relevant range: if orders surge and a second shop must be rented, rent jumps. Some costs carry both natures — a phone bill with a base charge plus usage fees — and are called semi-variable costs.
- Step 4: The idea of contributionContribution = sales revenue − variable costs; per unit, unit contribution = selling price − unit variable cost. Each sale's contribution first absorbs fixed costs; once they are covered, further contribution is profit. For example, a drink stall sells lemon tea at $18 a cup, with lemon, sugar and cup costing $6: the unit contribution is $12, which pays rent and wages first — and once they are paid, every extra cup adds $12 clean. Grasping contribution is the key to CVP analysis.
- Step 5: Computing the break-even pointThe break-even point is the volume at which profit is zero: break-even volume = fixed costs ÷ unit contribution; break-even sales value = fixed costs ÷ contribution ratio, where the ratio = unit contribution ÷ selling price. For example, with monthly fixed costs of $45,000, a $40 price and $25 unit variable cost, unit contribution is $15; break-even volume = 45,000 ÷ 15 = 3,000 units, or 3,000 × 40 = $120,000 in sales. At 2,999 units the firm still loses; at 3,001 it starts to profit.
- Step 6: Target profit and impact analysisTo reach a target profit, required volume = (fixed costs + target profit) ÷ unit contribution. For example, using the figures above, a $15,000 monthly target requires (45,000 + 15,000) ÷ 15 = 4,000 units. CVP analysis also does impact studies: if rent rises by $3,000, fixed costs become $48,000 and break-even 3,200 units; if the price falls by $2 with volume unchanged, unit contribution drops to $13 and break-even rises to about 3,462 units — so management can weigh the true cost of a price cut in advance.
- Step 7: Cost concepts in decision-makingDifferent decisions call for different costs. Sunk costs are paid and unrecoverable — irrelevant; opportunity cost is the best alternative forgone — must count; incremental costs are the extra costs a decision creates. For example, software bought last month for $50,000 no longer fits: that $50,000 is sunk and must not colour the decision to switch; but if switching means giving up the chance to resell the old licence for $20,000, that $20,000 is an opportunity cost to be charged against the new plan.
- Step 8: Marginal and absorption costingThe elective requires two ways of preparing income statements. Marginal costing puts only variable production costs into inventory, expensing all fixed production overheads in the period; absorption costing spreads fixed production overheads into inventory too. For example, when output exceeds sales, absorption costing leaves part of the fixed overheads in closing inventory to be expensed next period, so current profit looks higher than under marginal costing; both have merits and drawbacks you must be able to compare. The special-order decision flows from the marginal idea: with spare capacity, any price above unit variable cost adds to profit.
5Worked example Example
Millennium Stationery Factory produces hardcover notebooks at a selling price of $40 each, with unit variable cost of $25 and monthly fixed costs of $45,000. (a) Compute the monthly break-even point in units and in sales value. (b) If the target monthly profit is $15,000, how many notebooks must be sold each month?
- Unit contribution first: selling price − unit variable cost = $40 − $25 = $15.
- Break-even volume = fixed costs ÷ unit contribution = $45,000 ÷ $15 = 3,000 notebooks.
- Break-even sales value = 3,000 × $40 = $120,000.
- Required volume for target profit = (fixed costs + target profit) ÷ unit contribution = ($45,000 + $15,000) ÷ $15 = 4,000 notebooks.
- Check: 4,000 × $15 − $45,000 = $60,000 − $45,000 = $15,000, matching the target profit.
- Answer: (a) Unit contribution = $40 − $25 = $15; break-even volume = $45,000 ÷ $15 = 3,000 notebooks; break-even sales value = 3,000 × $40 = $120,000. (b) Required volume = ($45,000 + $15,000) ÷ $15 = 4,000 notebooks. So profit is exactly zero at 3,000 notebooks a month and reaches $15,000 at 4,000; below 3,000 the factory loses money, and management should treat 3,000 as the floor when monitoring sales.
6Common mistakes Mistakes
7Quick check Quick check
Q1Which of the following are variable costs: factory rent, packaging materials, piece-rate wages, supervisors' monthly salaries?
Q2How is unit contribution computed, and what is it used for?
Q3A product sells at $60 with unit variable cost of $36 and fixed costs of $28,800. What is the break-even volume?
Q4What is a sunk cost, and how should it be treated in decisions?
Q5With spare capacity, what is the minimum-price rule for accepting a special order?
8Recap Recap
- Cost accounting serves internal decisions: pricing, cost control and option appraisal
- Direct versus indirect is about traceability; fixed versus variable is about cost behaviour
- Contribution = sales revenue − variable costs; it absorbs fixed costs first, and the remainder is profit
- Break-even volume = fixed costs ÷ unit contribution; target-profit volume = (fixed costs + target profit) ÷ unit contribution
- Sunk costs are irrelevant; opportunity and incremental costs are the relevant ones