Overhead Allocation

The overhead allocation process assigns indirect manufacturing costs (factory rent, machinery depreciation, supervision, utilities) to individual products so that balance sheet inventory values and cost of goods sold reflect the full economic cost of production. The method chosen — direct labor-hours, machine hours, units produced — shapes reported profit and inventory value.

Why overhead allocation matters

Manufacturing firms incur two types of costs: direct (raw materials, direct labor that traces to a single product) and indirect (factory supervisor salaries, equipment depreciation, facility rent). A widget factory’s supervisor is necessary but not assignable to one widget; the factory rent must somehow be spread across all products.

Absorption costing, the standard for external financial reporting, requires that overhead be allocated to products. Under variable costing, only variable overhead is assigned; fixed overhead is treated as a period cost. The choice between methods significantly affects reported profit margin and inventory valuation.

Allocation bases and methods

The simplest approach is direct labor-hour allocation: if a factory incurs $100,000 in overhead and expects 10,000 direct labor-hours, the overhead rate is $10 per direct labor-hour. A product requiring 50 direct labor-hours receives $500 in allocated overhead.

Alternative bases include:

• Machine hours: used when production is capital-intensive (overhead is mainly depreciation and maintenance).
• Units produced: simplistic but used for homogeneous products.
• Material costs: sometimes used when overhead varies with material expense.

Activity-based costing (ABC) is more sophisticated: it identifies cost drivers (setup time, quality inspections, material handling) and allocates overhead to products based on actual consumption of those activities. A high-complexity product requiring frequent setups bears more overhead than a simple commodity product.

The two-stage process

Stage 1: Accumulate overhead in cost pools. Factory superintendent salary goes to “supervision” pool; equipment maintenance to “maintenance” pool; utilities split across pools by facility space. Each cost pool relates to a cost driver (or allocation base).

Stage 2: Assign overhead to products. Based on how much of each cost driver the product consumes, overhead is assigned. A custom order requiring 100 inspections bears more inspection-related overhead than a standard order requiring 5 inspections.

Practical example

A furniture maker produces dining tables and chairs in the same factory.

• Direct materials: tables $150/unit, chairs $20/unit.
• Direct labor: tables 10 hours @ $20/hour = $200; chairs 2 hours @ $20/hour = $40.
• Factory overhead (monthly): $30,000 (rent, utilities, supervision).
• Expected production: 500 tables, 2,000 chairs.

Using direct labor-hour allocation:

• Total direct labor-hours: (500 × 10) + (2,000 × 2) = 9,000 hours.
• Overhead rate: $30,000 / 9,000 = $3.33/hour.
• Table overhead: 10 × $3.33 = $33.30 per table.
• Chair overhead: 2 × $3.33 = $6.67 per chair.

Full absorption cost:

• Table: $150 + $200 + $33.30 = $383.30.
• Chair: $20 + $40 + $6.67 = $66.67.

If chairs actually require more machine setups (cost driver), ABC might assign more overhead to chairs, increasing their full cost — a more accurate picture of economic reality.

Impact on financial reporting

High overhead allocation increases inventory values on the balance sheet and cost of goods sold on the income statement. In a period when production exceeds sales, a large chunk of overhead is “capitalized” into inventory rather than expensed, boosting reported profit margin.

Conversely, if production drops but sales remain steady, overhead per unit rises (same factory costs, fewer units absorbing them), which can make profit appear to collapse even if sales volume is stable. This effect is called “overhead leverage” and is important for understanding earnings quality.

Activity-based costing vs. traditional methods

Absorption costing using a single plant-wide rate or departmental rates is easier to administer but can distort product costs. ABC identifies multiple cost drivers, providing richer data for pricing decisions and profitability analysis.

A bank might use activity-based costing to allocate processing, marketing, and servicing overhead to customer accounts. A high-maintenance business customer (frequent calls, complex orders) bears more allocated overhead than a transactional retail customer — enabling the bank to set appropriate fees and avoid unknowingly serving unprofitable clients.

Standards and adjustments

International Financial Reporting Standards (IFRS) and Generally Accepted Accounting Principles (GAAP) both require absorption of manufacturing overhead for inventory valuation. However, both allow variance between actual and applied overhead (due to capacity underutilization or inefficiency) — under-applied overhead increases period expense; over-applied overhead reduces it.