Core Principle: Only variable (direct) costs are assigned to products. Fixed indirect costs are treated as 'period costs' and charged in full against the total contribution of the period.
The Concept of Contribution: Contribution is defined as the difference between the selling price and the direct costs ().
Profit Generation: Profit is only realized once the total contribution from all units sold exceeds the total fixed indirect costs of the business.
Decision Utility: This approach is highly effective for short-term decisions, such as whether to accept a special one-off order at a lower-than-normal price.
| Feature | Full Costing | Contribution Costing |
|---|---|---|
| Cost Components | Direct + Indirect Costs | Direct Costs Only |
| Inventory Value | Includes a share of fixed overheads | Valued at variable cost only |
| Profit Focus | Net Profit per unit | Contribution per unit |
| Primary Use | External reporting & Long-term pricing | Internal decision-making & CVP analysis |
Inventory Impact: In periods where production exceeds sales, Full Costing will report a higher profit than Contribution Costing because some fixed costs are 'trapped' in unsold inventory.
Risk Assessment: Contribution costing highlights the 'break-even' point more clearly, showing exactly how many units must be sold to cover fixed obligations.
Reconciliation Formula: Always remember that the difference in profit between the two methods is equal to the change in inventory levels multiplied by the fixed overhead per unit ().
Identify the Base: In exam questions involving multiple products, look carefully for the 'allocation base' (e.g., % of output or labor hours) to correctly distribute indirect costs.
Sanity Check: If production is higher than sales, Full Costing profit MUST be higher than Contribution Costing profit. If your calculation shows otherwise, re-check your inventory valuation.
Terminology Alert: Be prepared for synonyms; 'Absorption Costing' is often used for Full Costing, and 'Marginal Costing' for Contribution Costing.
Arbitrary Allocation: A common mistake is assuming that indirect costs are always split equally. In reality, using an inappropriate base (like splitting rent by unit volume when one product takes up 90% of the space) leads to distorted pricing.
Ignoring Fixed Costs: In Contribution Costing, students often forget that fixed costs still need to be paid. A positive contribution does not guarantee a profit if it is too small to cover the total fixed overheads.
Volume Sensitivity: Full costing calculations are highly sensitive to the 'budgeted' output. If actual production is lower than expected, the business may 'under-absorb' its overheads, leading to an unexpected loss.
