Allocating shared factory fixed costs accurately is essential because misallocating overhead distorts individual product profitability, leading to flawed pricing strategies and poor product-mix decisions.
The primary methods used in industrial financial planning and cost accounting include:
1. Direct Labor Hours (DLH) Method
This traditional method distributes overhead based on the total direct labor hours required to manufacture each product line.
$$\text{Allocation Rate per Labor Hour} = \frac{\text{Total Shared Fixed Overhead Costs}}{\text{Total Direct Labor Hours Across All Products}}$$
$$\text{Allocated Cost for Product } i = \text{Allocation Rate} \times \text{Direct Labor Hours for Product } i$$
- Best For: Labor-intensive manufacturing environments where human labor drives overall facility operations.
- Limitation: In highly automated factories, direct labor represents a small fraction of total costs, making this driver arbitrary.
2. Machine Hours Method
This approach allocates shared overhead based on the total running time of plant machinery dedicated to each product.
$$\text{Allocation Rate per Machine Hour} = \frac{\text{Total Shared Fixed Overhead Costs}}{\text{Total Facility Machine Hours}}$$
$$\text{Allocated Cost for Product } i = \text{Allocation Rate} \times \text{Machine Hours for Product } i$$
- Best For: Capital-intensive, automated factories where machinery depreciation, equipment maintenance, and factory power represent the bulk of fixed overhead.
- Limitation: Ignores non-machine fixed costs like quality assurance or administrative overhead.
3. Activity-Based Costing (ABC)
Activity-Based Costing breaks down total fixed overhead into distinct activity pools (e.g., machine setups, material handling, quality inspections, plant maintenance) and assigns costs using specific activity drivers for each pool.
$$\text{Activity Rate for Pool } k = \frac{\text{Total Cost of Activity Pool } k}{\text{Total Capacity of Driver } k}$$
$$\text{Allocated Cost for Product } i = \sum_{k} \left( \text{Activity Rate}_k \times \text{Driver Usage}_k \text{ by Product } i \right)$$
- Best For: Complex multi-product facilities where products consume factory resources at significantly different frequencies or batch sizes.
- Limitation: Higher implementation cost and administrative complexity compared to traditional single-rate methods.
4. Direct Material Cost or Prime Cost Percentage Method
This method assigns fixed overhead in proportion to the raw material expenditure or prime cost (Direct Materials + Direct Labor) consumed by each product line.
$$\text{Allocation Rate (\%)} = \frac{\text{Total Shared Fixed Overhead Costs}}{\text{Total Direct Material Cost Across All Lines}} \times 100\%$$
$$\text{Allocated Cost for Product } i = \text{Allocation Rate (\%)} \times \text{Direct Material Cost of Product } i$$
- Best For: Production environments where raw material handling and storage dominate plant operations.
- Limitation: Products made from expensive raw materials absorb disproportionately high overhead, even if they consume minimal factory resources.
5. Production Volume (Units Produced) Method
This straightforward method divides shared overhead equally across all physical units produced.
$$\text{Allocated Cost per Unit} = \frac{\text{Total Shared Fixed Overhead Costs}}{\text{Total Units Produced Across All Lines}}$$
- Best For: Facilities producing simple, homogeneous product lines of similar size, complexity, and manufacturing cycle time.
- Limitation: Distorts cost accuracy if products vary substantially in manufacturing difficulty or resource usage.
Comparison of Allocation Methods
| Method | Key Cost Driver | Implementation Complexity | Primary Ideal Use Case |
| Direct Labor Hours | Direct labor hours worked | Low | Assembly-heavy, manual operations |
| Machine Hours | Equipment runtime | Low–Moderate | Automated, capital-intensive plants |
| Activity-Based Costing | Specific operational activities | High | Diverse, multi-product industrial plants |
| Direct Material Cost | Material expenditures | Low | Material-dominant manufacturing |
| Production Volume | Physical units output | Very Low | Uniform single-type product outputs |