Activity-Based Costing: How It Works and When to Use It

Activity-Based Costing (ABC) is a sophisticated approach to product costing that allocates overhead costs based on the activities that drive those costs, rather than using a single predetermined overhead absorption rate. ABC provides more accurate product costs and better information for pricing and decision-making — and is a key topic in ACCA Performance Management (PM) and CIMA management accounting exams.

Why Was ABC Developed?

Traditional absorption costing allocates overheads based on volume-related bases such as direct labour hours or machine hours. This works reasonably well when overheads are a small proportion of total costs and when products are similar in their complexity and resource consumption. However, as businesses have become more automated, overheads have grown as a proportion of total costs, and product ranges have diversified. Traditional methods increasingly distort product costs — over-costing simple, high-volume products and under-costing complex, low-volume products.

ABC, developed by Robert Kaplan and Robin Cooper in the 1980s, addresses this by tracing overhead costs to activities and then to products based on the actual consumption of those activities.

The ABC Process

The ABC process involves four key steps:

Step 1: Identify activities — Identify the main activities that consume overhead resources, such as setting up machines, processing purchase orders, quality inspection, or customer support.

Step 2: Assign costs to activity cost pools — Group overhead costs into cost pools based on the activities they relate to. For example, machine set-up costs are grouped in a "set-up" cost pool.

Step 3: Determine cost drivers — Identify the cost driver for each activity pool — the factor that drives the cost of that activity. For machine set-ups, the cost driver might be "number of set-ups". For purchase order processing, it might be "number of purchase orders".

Step 4: Calculate cost driver rates and assign costs to products — Divide the cost pool total by the total number of cost driver units to get a cost driver rate, then assign costs to products based on how many cost driver units each product consumes.

ABC vs Traditional Absorption Costing

The critical difference is in how overheads are allocated. Traditional absorption costing uses a single blanket rate based on one volume measure. ABC uses multiple cost driver rates based on actual activity consumption. For products that consume disproportionate amounts of non-volume activities (such as frequent machine set-ups for small batches, or extensive customer support), ABC provides a significantly more accurate product cost.

Advantages and Disadvantages of ABC

ABC provides more accurate product costs, better pricing decisions, clearer understanding of cost drivers, and can identify opportunities for cost reduction by highlighting high-cost activities. However, it is more complex and expensive to implement than traditional methods, requires significant data collection, and may not be cost-effective for small businesses or those with simple product ranges.

Frequently Asked Questions

When is ABC most beneficial?

ABC is most beneficial for organisations with diverse product ranges, significant overhead costs, products that differ substantially in complexity or volume, and where traditional costing appears to be distorting product costs and pricing decisions.

Is ABC used for external financial reporting?

No — ABC is an internal management accounting tool. For external financial reporting under IFRS or GAAP, absorption costing is required for inventory valuation.