Activity-Based Costing

Allocate overhead by the activities that actually consume it, not by a flat percentage of direct cost.

Time1 h
FormatSmall group
StageBreakdown

Activity-Based Costing: what it is and why it works

Activity-based costing allocates overhead according to the activities products actually consume, rather than as a flat percentage of direct labor or material. You list the activities that make up overhead, such as ordering, machine setups, inspection, storage, shipping and engineering changes, assign each a cost from time and rate data, and then link each product to the activities it uses. The result is a product cost that reflects how much support each product really requires. From there, you can identify activities that cost a lot but add little value and redesign or eliminate them.

Traditional overhead allocation tends to make high-volume, simple products look more expensive than they are and low-volume, complex products look cheaper. When overhead is large and product variety is high, those distortions can lead to wrong pricing, wrong make-or-buy choices and wrong product mix decisions. Activity-based costing corrects this by tracing cost to its causes. It requires more data than a single overhead rate, but a simplified version focused on the handful of activities that dominate overhead is usually enough. It complements cost Pareto analysis, which ranks direct costs, and complexity cost analysis, which uses activity data to price variety; its findings often lead into process redesign.

What you need

Total overhead costs by department or cost center
A list of the main support activities and their approximate share of time or resources
Activity driver data, such as number of setups, purchase orders, inspections, shipments or engineering changes per product
Product volumes and direct costs
Current overhead allocation method for comparison

What you get

A cost per activity and a cost per unit of activity driver
Product costs based on actual activity consumption
A comparison with traditionally allocated costs, showing over- and under-costed products
A list of expensive, low-value activities to redesign or eliminate

When to use it

When small complex products subsidize big simple ones and nobody knows.

How to do it, step by step

List the activities the product consumes: ordering, setting up, inspecting, storing, shipping.
Assign a cost to each activity from time and rate data.
Link activities to products by actual consumption, not allocation keys.
Find activities that cost much and add little.
Redesign or delete the expensive low-value activities.

Worked example: Sheet-metal electrical enclosures: standard versus custom

Illustrative scenario — figures are realistic but not from a real company.

A sheet-metal shop made electrical enclosures: a catalog range built in large batches and custom enclosures built to customer drawings in small lots. Overhead of $4.2 million a year was allocated at 180 percent of direct labor. Management believed custom work was the most profitable part of the business.

The team identified six main activities: machine setups, purchasing, first-article inspection, engineering drawing checks, storage and shipping.
Using time records and headcount, they costed each activity, for example about $210 per press brake or punch setup and $85 per purchase order.
They linked activities to products: custom enclosures used about four times as many setups per unit and almost all engineering drawing checks and first-article inspections.
Compared with the flat overhead rate, custom enclosures turned out to cost around 30 percent more than reported, while catalog enclosures cost roughly 10 percent less.
The team targeted the most expensive activities: drawing checks and setups for small custom lots.

Result. The company introduced an engineering fee for new custom designs, a minimum lot size, and quick-change tooling on the press brake. Custom work stayed in the portfolio, but at prices that reflected its real cost. The main lesson was that the flat overhead rate had quietly subsidized complexity for years.

Open it in the FieldKit Design to Cost app → Get the Design to Cost template pack — join the waitlist

Common pitfalls and how to avoid them

Trying to model every activity in detail from the start.Start with the five to eight activities that account for most overhead and refine only where decisions depend on it.
Using allocation keys instead of real activity data.Link products to activities through actual counts such as setups, orders or inspections.
Treating the results as a one-time study.Update activity costs and driver counts periodically, at least for the main activities.
Stopping at recalculated product costs.Use the analysis to redesign or eliminate costly activities, not just to reprice products.

Frequently asked questions

What is the difference between activity-based costing and traditional costing?

Traditional costing allocates overhead using a single base, often direct labor hours or machine hours. Activity-based costing first assigns overhead to activities, such as setups, purchasing or inspection, and then assigns activity costs to products according to how much of each activity they use. It gives a more accurate view when products differ strongly in complexity, batch size or support needs.

What is an activity driver in activity-based costing?

An activity driver is the measure used to assign an activity's cost to products, for example the number of setups, purchase orders, inspections, shipments or engineering changes. It should reflect what actually causes the activity to consume resources. Choosing a good driver is key to making the results credible and useful.

Is activity-based costing worth the effort for a small plant?

Often yes, if overhead is significant and products differ in complexity or batch size. A simplified model with a handful of activities can be built in days using existing data. It is less useful when products are very similar and overhead is small, because traditional allocation then gives similar results.