ABC: system overview and key concepts

Learning outcome statements

The learning outcome statements relevant for this section are:

1. define the nature of the system, understand the cost flows of the system, and identify its appropriate use
2. calculate inventory values and cost of goods sold
3. demonstrate an understanding of the proper accounting for normal and abnormal spoilage
4. discuss the strategic value of cost information regarding products and services, pricing, overhead allocations, and other issues
5. identify and describe the benefits and limitations of each cost accumulation system
6. define the elements of activity-based costing, such as cost pool, cost driver, resource driver, activity driver, and value-added activity
7. calculate product cost using an activity-based system, and compare and analyze the results with costs calculated using a traditional system
8. explain how activity-based costing can be utilized in service companies

Inventory valuation, spoilage accounting, and full activity-based product-cost calculations are covered in the chapters that follow this one.

Introduction

Definitions

Activity-based costing (ABC)

A cost accounting methodology that allocates overhead and indirect costs to products or services based on the activities that generate those costs.

Unlike traditional costing systems, which often rely on a single volume-based cost driver such as labor or machine hours, ABC recognizes that multiple activities consume resources in different ways. By tracing costs through activities to specific cost objects (products, services, or customers), ABC provides more accurate and actionable cost information.

How costs flow in ABC

ABC assigns costs in two stages. First, a resource driver traces resource costs, like factory rent, into activity cost pools based on how much of the resource each activity uses. Then an activity driver assigns the pooled costs to cost objects based on how much of the activity each one consumes.

Example: Two-stage cost assignment

Supervisor and equipment costs of $60,000 are traced to the setup activity pool using the resource driver: supervisor hours spent on setups. The pool is then assigned to products using the activity driver, number of setups. At 300 setups a year, the rate is $60,000 / 300 = $200 per setup, so Product A’s 50 setups are assigned 50 × $200 = $10,000.

Answer: $10,000 of setup cost goes to Product A. The next chapter, ABC: cost flows and product costing, covers the full per-unit calculation.

To understand how ABC functions, it’s essential to define its core components:

Element	Definition
Cost object	The item for which cost information is desired (e.g., product, service, customer)
Activity	Any task or function that consumes resources (e.g., machine setup, order processing)
Cost pool	A grouping of all costs associated with a particular activity
Cost driver	A factor that causes or relates to the cost of an activity (e.g., number of setups, inspections)
Resource driver	A measure used to assign resource costs to activities (e.g., labor hours to maintenance tasks)
Activity driver	A measure used to assign activity costs to cost objects (e.g., setups per product)
Value-added activity	An activity that increases the value of a product or service in the eyes of the customer
Non-value-added activity	An activity that does not enhance product value and may represent inefficiency

By tracing costs through these elements, ABC allows firms to understand the true cost structure of their offerings and take informed action to improve profitability.

ABC is most valuable when:

• Overhead is a significant portion of total cost
• There are multiple products or services with varying levels of complexity
• Traditional costing distorts product margins, leading to poor pricing or discontinuation decisions
• Management requires greater visibility into operational costs to support decision-making

Traditional costing often distorts margins because it spreads overhead using one volume-based driver, even though costs like setups and engineering changes are driven by complexity, not volume. That shifts cost onto high-volume, simple products and away from low-volume, complex ones - overcosting the simple products and undercosting the complex ones.

Benefits and limitations

• Benefits: more accurate product and customer costs, better pricing and product-mix decisions, and visibility into non-value-added activities
• Limitations: costly to design and maintain, subjective driver and pool choices, facility-sustaining costs (like building depreciation) still allocated somewhat arbitrarily, and possible adoption resistance

In service organizations such as consulting firms, banks, hospitals, and logistics providers, ABC helps identify high-cost clients, unprofitable services, or inefficient back-office processes.