Under variable costing, fixed manufacturing costs are expensed in the period they are incurred. If production exceeds sales, the company incurs the full amount of fixed costs for the period, but only the variable costs of the units sold are matched against revenue. This often results in a lower operating income compared to absorption costing, where a portion of fixed costs would have been capitalized into the unsold inventory.

Throughput costing is based on the theory of constraints, which posits that only direct materials are variable costs. Consequently, all other manufacturing costs, including direct labor and variable manufacturing overhead, are treated as period costs. This means they are expensed in the period they are incurred rather than being attached to the product. This approach aims to minimize inventory levels and focus on the speed of production through the bottleneck.

Variable and absorption costing are fundamental techniques used in manufacturing to determine the cost of products. Their primary application is inventory costing, which involves assigning manufacturing costs to units produced. This is crucial for accurate financial reporting, as it determines the value of ending inventory on the balance sheet and the cost of goods sold on the income statement, directly impacting the firm's reported profitability.

Operating income differs between absorption costing and variable costing primarily due to the treatment of fixed manufacturing overhead. When inventory levels change—specifically when production volume differs from sales volume—fixed costs are either deferred in inventory or released from it. If inventory levels remain constant, both methods will yield the same operating income because all fixed costs incurred are expensed in the same period.

When production equals sales, there is no change in inventory levels. Under both absorption and variable costing, the fixed manufacturing overhead costs are treated similarly in terms of the income statement impact because no fixed costs are deferred in or released from inventory. Consequently, the net income reported under both methods will be identical, as there is no fluctuation in the inventory balance to cause a divergence in profit recognition.

Actual costing is a valuation method that calculates the cost of a product or service by using the actual direct costs incurred. By multiplying the actual direct rates by the actual quantity of inputs, businesses can determine the precise historical cost of production. This method is highly accurate but may lead to fluctuations in unit costs due to variations in actual input prices and quantities over different periods.

When production is less than sales, the company is selling units from beginning inventory. Under absorption costing, these units carry fixed overhead costs from previous periods, which are now expensed. Variable costing, however, only expenses current period fixed costs. Consequently, when inventory is liquidated, absorption costing reports lower profits, making the operating income under variable costing appear relatively higher in comparison.

Under variable costing, fixed manufacturing overhead is treated as a period cost rather than a product cost. Because fixed costs are not attached to inventory, operating income is not affected by changes in production volume. Instead, operating income fluctuates solely based on the quantity of units sold, as this directly impacts the total contribution margin generated during the period. This makes variable costing a useful tool for short-term decision-making.

The actual costing method calculates product costs using the actual costs incurred for direct materials and direct labor. By multiplying the actual quantity of resources consumed by the actual prices paid for those resources, the firm captures the precise historical cost of production. This method is accurate but can lead to fluctuating unit costs due to variations in input prices and usage efficiency.

Variable costing, also known as direct costing, is a method where only variable manufacturing costs are included in the cost of inventory. Fixed manufacturing overhead costs are treated as period costs and are expensed in the period they are incurred, rather than being attached to the product units produced.