What it means
Traditional costing spreads overheads across products using a single blunt measure such as direct labour hours. Activity-based costing instead identifies what actually consumes resources, and the activity cost driver is the yardstick for that consumption.
Drivers usually fall into three types. Transaction drivers count how many times something happens, such as 1,200 setups; duration drivers measure how long it takes, such as inspection minutes; and intensity drivers capture the actual resources used on a specific job, which is the most accurate and the most expensive to track.
The business reason this matters is cross-subsidy. When overhead is spread by volume, high-volume simple products absorb costs they never caused while low-volume fiddly products look cheaper than they are, and pricing decisions built on those numbers quietly destroy margin.
Applying a driver takes two steps: divide the activity's cost pool by the total driver quantity to get a rate per driver unit, then multiply that rate by the driver units each product or customer consumed. The result is an overhead charge that reflects demand on the activity rather than sales volume.
The usual nuance is cost versus accuracy. Every extra driver adds tracking work, so most organisations settle on somewhere between five and fifteen drivers that explain the bulk of overhead, rather than pursuing perfect precision.
In practice
Real-world examples.
Example
A contract packer charges its warehouse costs to customers using pallet movements rather than sales value. A customer ordering many small drops immediately shows a higher cost to serve than a customer taking full pallets.
Example
A hospital finance team uses theatre minutes as the driver for operating room overhead. A short routine procedure is charged far less than a long complex one, which was not the case under the previous flat charge per case.
Example
A subscription software company uses number of support tickets as the driver for its customer success cost pool. Enterprise accounts that raise 40 tickets a quarter turn out to consume nine times more support cost than self-serve accounts, changing how the company prices its tiers.
Formula
Calculation
Activity Rate = Activity Cost Pool / Total Activity Cost Driver Quantity
Overhead Applied = Activity Rate x Driver Units Consumed
A components manufacturer has a machine setup cost pool of $180,000 a year covering setup technicians, tooling changes and lost machine time. Across all products the plant performs 1,200 setups a year, so the driver is number of setups.
Activity rate = $180,000 / 1,200 setups = $150 per setup.
Product A is a low-volume, high-variety line that needs 320 setups a year.
Overhead applied to Product A = 320 setups x $150 = $48,000.
Under the old system, setup costs were spread by machine hours and Product A absorbed only $19,000, because it uses the machines for short runs. The new driver reveals $29,000 of cost that was previously being carried by the high-volume lines.Case study
Seen in the real world.
Pinehill Instruments is a fictional maker of laboratory equipment, presented here as an illustrative case. It sold two lines, a high-volume standard meter and a low-volume customised analyser, and its accounts showed both earning healthy margins.
The finance manager rebuilt the setup cost pool of $180,000 and used number of setups as the activity cost driver. With 1,200 setups a year the rate came to $150 each, and the customised analyser alone accounted for 320 setups, drawing $48,000 of setup overhead against the $19,000 the old machine-hour method had assigned.
Once that $29,000 was moved onto the analyser, its apparent margin collapsed. Pinehill did not discontinue the line but raised its price, set a minimum batch size to cut setup frequency, and started quoting new custom work with a setup charge itemised separately.
Watch out
Common mistakes.
- Picking a driver because the data is easy to obtain rather than because it genuinely causes the cost, which reproduces the distortions activity-based costing was meant to remove.
- Using a single driver for a mixed cost pool, for example charging both machine setup and quality inspection on the same setup count when inspections are triggered by something else.
- Building dozens of drivers in pursuit of precision until the costing system becomes too slow and expensive to maintain, so nobody updates it.
Questions
People also ask.
What is the difference between a cost driver and a cost pool?
The pool is the bucket of money for an activity, and the driver is the measure used to divide that bucket among products or customers.
Can one activity have more than one driver?
In principle yes, but in practice a pool with two genuine drivers is usually a sign it should be split into two separate pools.
How often should driver rates be recalculated?
Most organisations refresh them annually with the budget, and more often if volumes or processes change materially during the year.
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