Activity-Based Costing: More Accurate Product Cost Allocation

Traditional overhead allocation uses a single, volume-based rate (like direct labour hours) to assign all overhead costs to products. This works well when products are similar and overhead is predominantly driven by volume. But in modern businesses, where products vary greatly in complexity, a single rate produces distorted costs — overcosting simple products and undercosting complex ones.

Activity-Based Costing (ABC) solves this by identifying the specific activities that drive overhead costs and assigning costs based on each product’s actual consumption of those activities.

ABC vs. Traditional Costing: Core Difference

Traditional: One overhead pool → one allocation rate → apply to all products uniformly.

ABC: Multiple cost pools (one per activity) → cost driver rate per activity → apply based on each product’s actual activity use.

The ABC Process

1. Identify activities — Machine set-ups, purchase ordering, quality inspection, customer support, engineering changes.
2. Assign overhead costs to activity cost pools — Group costs by the activity that causes them.
3. Determine cost drivers — The measurable factor that drives each activity’s cost (number of set-ups, number of purchase orders, inspection hours).
4. Calculate activity rates = Cost Pool ÷ Total Cost Driver Units.
5. Assign costs to products — Multiply activity rate × each product’s use of the cost driver.

Worked Example

Two products: Product A (high-volume, simple) and Product B (low-volume, complex).

Activity: Machine Set-Ups
Cost pool: $200,000. Total set-ups: 100.
Rate: $2,000 per set-up.
Product A uses 10 set-ups → $20,000 overhead.
Product B uses 90 set-ups → $180,000 overhead.

Under traditional costing (by volume), Product A (80% of units) absorbs $160,000 — a severe overstatement. ABC reveals Product B’s true cost.

Benefits of ABC

• More accurate product profitability analysis
• Better pricing decisions — charge complex products their true cost
• Identifies which activities add value and which are wasteful
• Supports process improvement initiatives

Limitations

• Expensive and time-consuming to implement
• Requires significant data collection and maintenance
• Can be overkill for simple product ranges

Lesson Summary

• ABC assigns overhead via multiple activity-based cost pools — far more accurate than a single volume-based rate.
• Process: identify activities → assign costs → find cost drivers → calculate rates → apply to products.
• Best suited for organisations with diverse products and significant overhead costs.

Why Traditional Costing Distorts Product Costs

Traditional overhead allocation uses a single plantwide rate (e.g., machine hours) applied to all products equally. The problem: not all products consume overhead in proportion to machine hours. A complex low-volume product might use far more machine setups, quality inspections, and engineering time than a high-volume simple product — but if you only charge by machine hours, the simple product subsidises the complex one.

ABC fixes this by identifying the specific activities that cause costs and assigning costs based on actual activity consumption.

Full ABC Analysis: FusionTech Inc.

FusionTech makes two products: Standard Widget (5,000 units) and Custom Widget (500 units).

Under traditional costing (allocated by machine hours), Standard Widget would absorb 80% of total overhead, giving it an artificially high cost. ABC reveals the Custom Widget is the true overhead driver — critical for pricing and profitability decisions.