Variable costs are expenses that change in direct proportion to the volume of goods produced or services delivered. When output increases, total variable costs rise; when output falls, they decrease. The variable cost per unit remains approximately constant.
Understanding variable costs is essential for break-even analysis, pricing decisions, budgeting, and management accounting. Together with fixed costs, they determine the total cost structure of a business.
Examples of Variable Costs
| Variable Cost | Sector | How It Varies |
|---|---|---|
| Raw materials | Manufacturing | More units produced = more materials consumed |
| Direct labour (piece rate or hourly) | Manufacturing, services | More units = more labour hours |
| Packaging | Retail, wholesale | Each item sold requires packaging |
| Freight outwards | Distribution | More deliveries = higher transport costs |
| Sales commission | All sectors | Percentage of each sale |
| Credit card processing fees | Retail, e-commerce | Percentage of each transaction |
| Royalties per unit | Publishing, licensing | Paid per unit sold |
| Subcontractor costs | Construction, services | Engaged per project or job |
Variable Costs Versus Fixed Costs
| Feature | Variable Costs | Fixed Costs |
|---|---|---|
| Behaviour | Change with output | Stay constant within a range |
| Per-unit cost | Roughly constant | Decreases as output increases |
| Total cost at zero output | Zero | Unchanged |
| Examples | Materials, piece-rate wages | Rent, insurance, salaried staff |
| Risk profile | Lower (reduce with lower sales) | Higher (must be paid regardless) |
| Management focus | Efficiency, purchasing | Utilisation, capacity |
Calculating Total Variable Cost
Total Variable Cost = Variable Cost Per Unit x Number of Units
Worked Example
A bakery produces loaves of bread with the following variable costs:
| Cost Element | Per Loaf (£) |
|---|---|
| Flour and ingredients | 0.80 |
| Direct labour | 0.40 |
| Packaging | 0.10 |
| Energy (oven usage per loaf) | 0.15 |
| Total variable cost | 1.45 |
If the bakery produces 10,000 loaves in a month:
Total Variable Cost = £1.45 x 10,000 = £14,500
If production increases to 15,000 loaves:
Total Variable Cost = £1.45 x 15,000 = £21,750
The cost per loaf stays at £1.45, but total variable costs increase by £7,250.
Variable Costs and Contribution Margin
The contribution margin is the difference between the selling price and the variable cost per unit:
Contribution Per Unit = Selling Price - Variable Cost Per Unit
This contribution first covers fixed costs and then generates profit. It is the foundation of break-even analysis.
Using the bakery example, if each loaf sells for £3.00:
| Item | £ |
|---|---|
| Selling price | 3.00 |
| Variable cost | 1.45 |
| Contribution | 1.55 |
Contribution Margin Ratio = £1.55 / £3.00 = 51.7%
For every £1 of turnover, 51.7p contributes toward fixed costs and profit.
Variable Costs on the Income Statement
In a standard UK income statement under the Companies Act 2006, costs are classified by function (cost of sales, distribution, administration) rather than by behaviour. Variable costs are spread across these categories:
| Cost Category | Variable Element | Fixed Element |
|---|---|---|
| Cost of goods sold | Raw materials, direct labour | Factory rent, supervisor salaries |
| Distribution costs | Delivery fuel, packaging | Warehouse rent, vehicle insurance |
| Administrative expenses | (Usually minimal) | Salaries, rent, insurance |
For internal management accounting purposes, a marginal costing income statement separates costs by behaviour:
| Line | £ |
|---|---|
| Turnover | 300,000 |
| Variable costs | (145,000) |
| Contribution | 155,000 |
| Fixed costs | (100,000) |
| Net profit | 55,000 |
This format makes the contribution and the impact of volume changes immediately visible.
Semi-Variable Costs
Some costs have both fixed and variable elements:
| Cost | Fixed Element | Variable Element |
|---|---|---|
| Electricity | Standing charge | Usage charge per kWh |
| Telephone | Line rental | Call charges |
| Maintenance | Service contract | Call-out charges |
| Vehicle costs | Insurance, road tax | Fuel, tyres |
| Staffing (with overtime) | Basic salary | Overtime premium |
For break-even and budgeting purposes, semi-variable costs must be split into their fixed and variable components. The high-low method is a simple technique:
Variable Rate = (Highest Total Cost - Lowest Total Cost) / (Highest Activity - Lowest Activity)
Example
| Month | Units Produced | Electricity Cost (£) |
|---|---|---|
| January (low) | 8,000 | 2,400 |
| July (high) | 14,000 | 3,600 |
Variable Rate = (£3,600 - £2,400) / (14,000 - 8,000) = £0.20 per unit
Fixed Element = £2,400 - (8,000 x £0.20) = £800 per month
Reducing Variable Costs
| Strategy | How It Reduces Variable Costs |
|---|---|
| Bulk purchasing | Lower per-unit material prices |
| Supplier negotiation | Better terms and prices |
| Process efficiency | Less waste, fewer defective units |
| Automation | Replaces variable labour with fixed machine costs |
| Alternative materials | Cheaper materials without compromising quality |
| Outsourcing | Converting in-house variable labour to a potentially lower external rate |
Reducing variable costs per unit lowers the break-even point and increases the contribution margin, directly improving profitability.
Variable Costs and Pricing
Marginal Cost Pricing
In the short term, a business can accept orders at any price above variable cost because each sale makes a positive contribution. This is called marginal cost pricing and is used when:
- The business has spare capacity
- The order does not displace higher-margin sales
- The customer will not expect the low price permanently
However, in the long term, prices must cover both variable and fixed costs to sustain the business.
Full Cost Pricing
Full Cost Per Unit = Variable Cost Per Unit + (Total Fixed Costs / Expected Units)
Using the bakery example with fixed costs of £15,000 per month and expected production of 10,000 loaves:
| Item | £ |
|---|---|
| Variable cost per loaf | 1.45 |
| Fixed cost per loaf (£15,000 / 10,000) | 1.50 |
| Full cost per loaf | 2.95 |
The selling price of £3.00 gives a profit margin of £0.05 per loaf (1.7%), which may prompt a review of pricing or cost structure.
Variable Costs and Corporation Tax
Variable costs are fully deductible for corporation tax purposes as trading expenses, provided they are incurred wholly and exclusively for the purposes of the trade. There are no special tax adjustments for variable costs – the distinction between variable and fixed is a management accounting classification, not a tax one.
However, the stock valuation for tax purposes must include both variable production costs and a fair proportion of fixed production overheads under the absorption costing requirement of FRS 102 Section 13. Using marginal costing to value stock (excluding fixed overheads) is not permitted for statutory or tax accounts.
Variable Costs in Different Sectors
| Sector | Primary Variable Costs | Typical Variable Cost as % of Turnover |
|---|---|---|
| Manufacturing | Materials, direct labour | 40-70% |
| Retail | Purchase cost of goods | 50-75% |
| Construction | Materials, subcontractors | 60-80% |
| Professional services | Direct staff time | 30-50% |
| Software | Hosting, support | 10-25% |
| Hospitality | Food and beverage costs | 25-40% |
Businesses with lower variable costs as a percentage of turnover have higher contribution margins and reach break-even at lower sales volumes, but they typically have higher fixed costs (salaries, technology, premises).