Approaches to costing: full, contribution

Contribution is the amount left from a product's selling price once its variable cost has been covered — found as selling price per unit minus variable cost per unit. It 'contributes' towards paying the firm's fixed costs and then towards profit; for example, a $20 product with $12 variable cost gives a contribution of $8 per unit.

Contribution is selling price minus variable cost — the surplus a product earns over its variable cost. Profit is what remains after all costs, including fixed costs, are covered. The difference is that contribution must first pay the firm's fixed costs, and only what is left becomes profit: profit = total contribution − total fixed costs. So a firm can earn a large total contribution but only a small profit (or even a loss) if its fixed costs are high.

A business would use contribution costing when making a special order decision — for example, deciding whether to accept a one-off order at a price below the normal price. Under contribution costing, the firm compares the order's price with the variable cost per unit. If the price is above the variable cost, each unit makes a positive contribution towards the fixed costs the firm has to pay anyway, so the order adds to profit even at a low price.

Full costing would be unhelpful here because it loads a share of fixed overheads onto the order; this could make the order look unprofitable when, in the short run, those overheads exist whether or not the order is accepted. Provided the firm has spare capacity (so the order does not displace full-price sales), contribution costing gives the correct short-run decision: accept the order if its price exceeds the variable cost per unit.

Full (absorption) costing allocates all costs — direct costs plus a share of overheads — to each product, and this has several genuine uses. It gives a complete cost per product, which is the basis of cost-plus pricing: by adding a mark-up to the full cost, a firm ensures its prices cover all its costs, including overheads, across the whole product range. It is also required for financial reporting — valuing inventory and calculating profit in the accounts — and it forces the firm to recognise that overheads must ultimately be paid.

However, the method has important limitations. The central problem is that overhead allocation is arbitrary: overheads are not naturally attached to one product, so they are spread using a chosen basis (labour hours, machine hours, proportion of direct costs). A different basis gives a different 'full cost', so the figure can mislead. A product might be loaded with too much overhead and appear unprofitable, leading the firm to drop a product that actually makes a positive contribution. Full costing is therefore less useful for short-run decisions, where fixed overheads are unavoidable and should be ignored.

Therefore full costing is useful for pricing the whole range and for financial reporting, but its arbitrary overhead allocation limits its reliability for individual product decisions, where contribution costing is more appropriate.

Contribution costing charges only variable costs to products and measures the contribution (selling price − variable cost) each unit makes towards fixed costs and profit. Its usefulness depends on the decision the manufacturer is making.

The case that it is useful. Contribution costing is excellent for short-run decisions. For a special order, the firm accepts it if the price exceeds the variable cost per unit, because each unit then adds positive contribution towards unavoidable fixed costs. It is also valuable for make-or-buy decisions, for choosing between products (rank by contribution), and for deciding whether to drop a product — a product making a positive contribution should usually be kept even if full costing shows a 'loss', because dropping it would leave the fixed costs uncovered. It is also the basis of break-even analysis. Crucially, it avoids the arbitrary overhead allocation of full costing, giving cleaner figures for decisions.

The case against / limitations. Contribution costing ignores fixed costs in the per-product figure, so if a manufacturer used it to set long-run prices, it would price too low and fail to cover overheads, making an overall loss. It assumes fixed and variable costs can be cleanly separated, which semi-variable costs blur. The special-order logic also assumes spare capacity — if an extra order displaces full-price work, the lost contribution must be deducted. And it cannot be used for financial reporting, which requires full costing.

Judgement. Contribution costing is highly useful for short-run decision-making — special orders, product choice, make-or-buy and break-even — where fixed costs are unavoidable and only contribution changes with the decision. It is not suitable on its own for long-run pricing or financial reporting. The most defensible position is that contribution costing should be used alongside full costing: contribution costing for decisions, full costing for normal pricing and accounts. Its usefulness therefore depends entirely on the purpose — it is the right tool for short-run choices, the wrong tool for setting standard prices.

Whether to accept a low-price special order is a classic contribution-costing decision. Because the price is above the variable cost per unit, each order unit makes a positive contribution, which on the surface argues for acceptance. But the right answer depends on capacity, the long-run consequences and the firm's objectives.

The case for accepting the order. With spare capacity, the firm's fixed costs are being paid whether or not the order is taken. Since the order's price exceeds the variable cost per unit, every unit of the order adds extra contribution towards those fixed costs and therefore raises total profit (or reduces a loss). The order also uses idle resources, may build a relationship with a new customer, and could lead to repeat full-price business. In purely short-run financial terms, a positive contribution with spare capacity means the order adds to profit.

The case against accepting the order. First, the 'positive contribution' logic only holds if there is genuinely spare capacity. If the order displaces existing full-price sales, the firm sacrifices their higher contribution, and the decision could reduce profit. Second, there are long-run risks: existing customers may discover the lower price and demand discounts, eroding margins across the board; the new customer may expect the low price to continue. Third, accepting work below normal price can signal the firm is desperate and may damage its brand or pricing power. Fourth, the order must not breach the firm's objectives (e.g. a premium-positioning strategy).

Weighing it up (criterion). The decision depends on whether the spare capacity is real and the long-run effects on normal pricing. If capacity is genuinely idle and the order is clearly one-off and confidential, accepting it is financially sound because it adds contribution at no opportunity cost. If accepting it would displace full-price work or undermine the firm's normal prices, the lost or eroded contribution can outweigh the gain.

Judgement. The business should accept the order to a significant extent — but only if it has genuine spare capacity and can protect its normal prices from the precedent the low price sets. The deciding criterion is opportunity cost plus the long-run effect on the firm's pricing: with idle capacity and no knock-on to other customers, the positive contribution makes acceptance the correct short-run decision; where the order displaces full-price sales or threatens the firm's pricing structure, it should be refused despite the positive contribution. So the simple rule 'accept if price exceeds variable cost' is right only once the spare-capacity and long-run conditions are met.