What it means
Traditional costing spreads overheads using a single driver such as labour hours or machine hours. That worked when overheads were small and mostly driven by direct labour, but in a business where setup, inspection, scheduling and customer service dominate the cost base it distorts everything.
High-volume simple products end up carrying costs caused by low-volume complex ones. Activity-based costing fixes this in four steps.
Identify the activities that consume resources, group their costs into pools, pick a driver that measures the use of each activity, then divide each pool by its total driver volume to get a rate per unit of activity. Each product or customer is then charged at those rates for what it actually used.
The business value sits in the decisions it changes. Pricing, product rationalisation, make-or-buy choices, minimum order sizes and customer profitability all look different once small and fiddly orders carry the cost of the attention they absorb.
Many businesses find that a handful of customers or product lines consume most of the overhead while contributing very little margin. The price of the method is effort and data.
Driver volumes have to be counted, activities have to be defined sensibly, and the whole exercise goes stale if nobody refreshes it, which is why many firms run it as a periodic study rather than a monthly routine. A simplified version with five to ten well-chosen activities usually captures most of the insight at a fraction of the work.
Two cautions are worth noting. Activity-based costing reallocates overheads rather than removing them, so a line that looks unprofitable on the new numbers may still be absorbing costs that would not disappear if it were dropped.
The same three letters also stand for other things in business writing, including the ABC method of inventory classification, so confirm which one a document means.
In practice
Real-world examples.
Example
A specialty food manufacturer runs 40 recipes on one line. An activity-based study shows that twelve low-volume lines consume most of the changeover time, and once setup cost is charged where it arises, four of them are loss-making. Two are discontinued and two are repriced with a higher minimum order quantity.
Example
A professional services firm charges overheads to clients as a flat percentage of fees. Rebuilding the numbers around activities such as onboarding, billing queries and out-of-scope meetings shows that its three smallest clients absorb nearly as much support as its largest. The partners introduce a minimum annual fee rather than dropping anyone.
Example
An online retailer treats warehouse cost as a cost per order. An activity view splits it into picking, packing and returns handling, and reveals that one apparel category carries a return rate so high that its contribution is negative. Sizing guidance is improved before the range is cut.
Formula
Calculation
Activity rate = cost pool divided by total driver volume, and overhead charged to a product = activity rate x driver units used by that product. A components factory has $900,000 of overheads. Under its old method it spread this over 90,000 direct labour hours, giving $900,000 / 90,000 = $10 per hour, so product X, which used 800 hours, carried $10 x 800 = $8,000. Under activity-based costing the overheads split into a setup pool of $600,000 across 30,000 setups, giving $600,000 / 30,000 = $20 per setup, and an inspection pool of $300,000 across 15,000 inspections, giving $300,000 / 15,000 = $20 per inspection. Product X needs 500 setups and 300 inspections, so it is charged 500 x $20 = $10,000 plus 300 x $20 = $6,000, a total of $16,000, which is double the old figure. Spread over the 2,000 units produced, overhead per unit moves from $8,000 / 2,000 = $4 to $16,000 / 2,000 = $8, which is enough to turn a thin margin negative.Case study
Seen in the real world.
Verity Labels is a fictional print business used here as an illustration. It absorbed $1,500,000 of overheads on machine hours and reported a healthy average gross margin of 34% across every customer.
An activity-based review built three pools, which were setup, artwork proofing and small-order handling. Charged on that basis, its twenty largest customers turned out to be more profitable than reported, while around sixty small accounts with frequent artwork changes were barely covering their own activity costs.
Management did not simply drop the small accounts, because much of the overhead would have remained. Instead it set a minimum order value, charged separately for artwork revisions beyond the second, and moved two staff from proofing to new business, which lifted reported profit within two quarters.
Watch out
Common mistakes.
- Believing activity-based costing reduces overheads, when it only reallocates them to the products and customers that cause them.
- Building forty activities and thirty drivers, which produces a model nobody maintains and nobody trusts.
- Dropping a product the moment it looks unprofitable, without checking which of its costs would actually disappear.
Questions
People also ask.
What is a cost driver?
The measure of how much of an activity something uses, for example the number of setups, inspections, orders or deliveries.
Is it worth it for a small business?
Often yes in a simplified form, because even a rough study of five activities tends to expose which customers or products absorb disproportionate effort.
How often should it be redone?
Typically once a year or whenever the product mix, process or cost base shifts enough that the old driver volumes no longer describe the business.
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