Activity-Based Costing
More accurate overhead allocation.
Why This Matters
Traditional costing assigns overhead using a single, company-wide rate — typically based on direct labor hours or machine hours. This was reasonable in 1920 when direct labor was 60–70% of product cost and overhead was a minor supplement. Today, in many businesses, overhead is the dominant cost and direct labor is a small fraction.
When overhead is large and products consume it in very different ways, a single rate produces cost cross-subsidization — simple, high-volume products are overcosted, and complex, low-volume products are undercosted. Managers then make pricing, product mix, and outsourcing decisions based on costs that are systematically wrong.
Activity-Based Costing (ABC) fixes this by assigning overhead in proportion to the actual activities that cause it. Instead of one rate for everything, ABC uses multiple rates — one for each major overhead-driving activity.
ABC doesn't change how much overhead exists — it changes how honestly that overhead is assigned to products. Companies that implement ABC often discover that their most "profitable" product lines are actually loss-makers, and vice versa. It's not a small adjustment — it rewrites the business's entire profit picture.
The Traditional Costing Problem
ABC Coffee Shop makes two products: Espresso Drinks and Catering Packs.
THE CROSS-SUBSIDIZATION TRAP
| Espresso | Catering Packs | |
|---|---|---|
| Units produced | 60,000 cups | 200 packs |
| Direct labor hours/unit | 0.025 hrs | 2.0 hrs |
| Total DL hours | 1,500 hrs | 400 hrs |
| Combined DL hours | 1,900 total | |
TRADITIONAL COSTING (single rate based on DL hours):
Total overhead: $36,305
Total DL hours: 1,900
POHR = $36,305 ÷ 1,900 = $19.11/DLH
Overhead per unit:
Espresso: 0.025 hrs × $19.11 = $0.48/cup
Catering: 2.0 hrs × $19.11 = $38.22/pack
IS THIS ACCURATE? Order processing, setups, inspections, and storage consume overhead proportional to orders and setups — not labor hours. The traditional rate allocates overhead based on the wrong driver.
Cross-Subsidization Under Traditional Costing
High-volume simple products carry excess overhead; complex low-volume products appear more profitable than they truly are.
The ABC Solution: Activities and Cost Drivers
ABC METHODOLOGY
STEP 1: Identify major activities that cause overhead costs.
STEP 2: Assign overhead costs to activity cost pools.
STEP 3: Identify the cost driver for each activity.
STEP 4: Calculate an activity rate (cost pool ÷ total driver units).
STEP 5: Apply costs to products based on their driver consumption.
Full ABC Example: ABC Coffee Shop
STEP 1 & 2 — ACTIVITY COST POOLS
| Activity | Cost Pool | Cost Driver | Total Driver |
|---|---|---|---|
| Order processing | $8,000 | Number of orders | 2,200 orders |
| Equipment setup | $6,500 | Number of setups | 130 setups |
| Machine running | $12,000 | Machine hours | 3,000 hrs |
| Quality inspection | $5,800 | Inspection hours | 400 hrs |
| Facility costs | $4,005 | Square footage | 2,000 sq ft |
| Total overhead | $36,305 | ||
STEP 3 & 4 — ACTIVITY RATES
| Activity | Cost Pool | ÷ Driver Total | = Activity Rate |
|---|---|---|---|
| Order processing | $8,000 | 2,200 orders | $3.64/order |
| Equipment setup | $6,500 | 130 setups | $50.00/setup |
| Machine running | $12,000 | 3,000 mach-hrs | $4.00/mach-hr |
| Quality inspection | $5,800 | 400 insp. hrs | $14.50/insp-hr |
| Facility costs | $4,005 | 2,000 sq ft | $2.00/sq ft |
STEP 5 — APPLY TO PRODUCTS
| Activity | Espresso (60K units) | Catering (200 units) |
|---|---|---|
| Order processing | 85,000 × $3.64 → $5.16/cup | 200 × $3.64 → $3.64/pack |
| Equipment setup | 30 × $50 → $0.025/cup | 100 × $50 → $25.00/pack |
| Machine running | 2,500 hrs → $0.167/cup | 500 hrs → $10.00/pack |
| Quality inspection | 100 hrs → $0.024/cup | 300 hrs → $21.75/pack |
| Facility costs | 1,600 sq ft → $0.053/cup | 400 sq ft → $4.00/pack |
| TOTAL OVERHEAD PER UNIT | $5.43/cup | $64.39/pack |
Note on the Example
In practice, "orders" for a coffee shop's individual drinks would be aggregated into daily batches — this example demonstrates the mechanics. The key insight is that catering packs get far more overhead per unit than the traditional rate suggested.
Interactive Tool
Build activity pools, calculate rates, and assign overhead to products — then compare ABC results to traditional single-rate costing.
ABC Allocator
Pre-filled with ABC Coffee Shop data. Edit activity pools, cost drivers, and product consumption to see activity rates and overhead per unit update instantly — then compare to traditional single-rate costing.
Step 1 & 2 — Activity Cost Pools
| Activity | Cost Pool ($) | Cost Driver | Driver Total | Activity Rate |
|---|---|---|---|---|
| Order processing | Number of orders | $3.64 | ||
| Equipment setup | Number of setups | $50.00 | ||
| Machine running | Machine hours | $4.00 | ||
| Quality inspection | Inspection hours | $14.50 | ||
| Facility costs | Square footage | $2.00 | ||
| Total overhead | Pool sum: $36,305.00 | |||
Step 5 — Apply Costs to Products (driver consumption)
Espresso Drinks
| Activity | Driver Used | × Rate | Assigned OH | ÷ Units | OH/Unit |
|---|---|---|---|---|---|
| Order processing | $3.64 | $309,090.91 | 60,000 | $5.15 | |
| Equipment setup | $50.00 | $1,500.00 | 60,000 | $0.03 | |
| Machine running | $4.00 | $10,000.00 | 60,000 | $0.17 | |
| Quality inspection | $14.50 | $1,450.00 | 60,000 | $0.02 | |
| Facility costs | $2.00 | $3,204.00 | 60,000 | $0.05 | |
| Total ABC overhead | $325,244.91 | $5.42/unit | |||
Catering Packs
| Activity | Driver Used | × Rate | Assigned OH | ÷ Units | OH/Unit |
|---|---|---|---|---|---|
| Order processing | $3.64 | $727.27 | 200 | $3.64 | |
| Equipment setup | $50.00 | $5,000.00 | 200 | $25.00 | |
| Machine running | $4.00 | $2,000.00 | 200 | $10.00 | |
| Quality inspection | $14.50 | $4,350.00 | 200 | $21.75 | |
| Facility costs | $2.00 | $801.00 | 200 | $4.01 | |
| Total ABC overhead | $12,878.27 | $64.39/unit | |||
TRADITIONAL vs. ABC — OVERHEAD PER UNIT
Traditional POHR = $36,305.00 ÷ 1,900 DL hrs = $19.11/DLH
| Product | Traditional OH/Unit | ABC OH/Unit | Difference | Verdict |
|---|---|---|---|---|
| Espresso Drinks | $0.48 | $5.42 | +4.94 (+1034.8%) | Undercosted (traditional) |
| Catering Packs | $38.22 | $64.39 | +26.18 (+68.5%) | Undercosted (traditional) |
Catering packs: traditional $38.22/pack vs. ABC $64.39/pack — complex, low-volume products absorb far more overhead under ABC.
ABC vs. Traditional: The Revelation
OVERHEAD PER UNIT COMPARISON
| Traditional Rate | ABC Rate | Difference | |
|---|---|---|---|
| Espresso drink | $0.48/cup | lower | Overcosted |
| Catering pack | $38.22/pack | $64.39/pack | +68.4% undercosted! |
Under traditional costing, catering packs appeared to cost $38.22 in overhead. Under ABC, the true cost is $64.39. If catering packs were priced at $60 (with traditional costing suggesting reasonable margin), ABC reveals that price doesn't even cover overhead — the product is priced at a loss.
This is the core value of ABC: exposing cross-subsidization. Espresso (high volume, simple) was SUBSIDIZING catering (low volume, complex) under the traditional system.
Customer Profitability with ABC
ABC can also be applied to customers rather than products:
ABC CUSTOMER PROFITABILITY ANALYSIS
| Walk-in Customers | Corporate Accounts | |
|---|---|---|
| Sales revenue | $102,000 | $68,000 |
| Product cost | ($61,200) | ($40,800) |
| Gross margin | $40,800 | $27,200 |
| Activity costs assigned to customer type: | ||
| Order processing | ($12,240) | ($20,060) |
| Delivery/logistics | $0 | ($8,500) |
| Account management | $0 | ($9,200) |
| Collections | ($1,800) | ($5,300) |
| Customer profit | $26,760 | ($15,860) |
REVELATION: Corporate accounts, which represent 40% of revenue and appeared to generate $27,200 in gross margin, are actually UNPROFITABLE by $15,860 after accounting for the high activity costs they generate. Walk-in customers subsidize the corporate account program.
Management can now: reprice corporate accounts, renegotiate service terms, or eliminate the most costly accounts. Without ABC, this was invisible.
When to Use ABC
ABC Is Most Valuable When
- Overhead costs are large relative to direct costs
- Product/customer diversity is high
- Overhead consumption varies significantly across products
- Traditional costing has been producing questionable margins
- Competitive pressure requires precise cost knowledge
ABC May Not Be Worth the Cost When
- Products are homogeneous (process costing is sufficient)
- Overhead is a small portion of total cost
- The business has a single product line
- Information needs are simple
- Implementation cost > accuracy benefit
The ABC Cost-Benefit Test
"Does the cost of running this more complex system produce decisions that are materially better than those from the simpler traditional system?"
If a 5% cost difference changes your decision: YES, use ABC. If decisions are the same regardless: the simpler system is fine.
Implementing ABC: A Practical Roadmap
Map the value chain
Walk through every step from raw materials to delivery. Each step that consumes resources is a candidate activity.
Group activities into cost pools
Combine similar activities. Five to eight pools is typical — enough detail without drowning in complexity.
Select cost drivers
Choose the measure that best explains why each pool's costs exist: orders, setups, machine hours, inspections, square footage.
Collect driver data
Gather actual consumption per product or customer. ERP systems, time studies, and operational logs are common sources.
Calculate and apply rates
Divide each pool by total driver units. Multiply each product's consumption by the rate. Compare to traditional costing.
Act on the insights
Reprice undercosted products, renegotiate unprofitable customers, eliminate loss-making SKUs, or redesign processes.
Common Mistakes
Mistake 1: Using Too Many Activity Pools
❌ WRONG
Creating 50+ activity pools with unique drivers for every micro-task. Data collection becomes impossible and rates fluctuate wildly.
✅ RIGHT
Focus on the 5–8 activities that drive 80%+ of overhead. Aggregate minor activities into broader pools. ABC should clarify decisions, not create a data nightmare.
Mistake 2: Choosing the Wrong Cost Driver
❌ WRONG
Using "number of units produced" as the driver for setup costs. Setups happen per batch, not per unit — the driver doesn't match the cause.
✅ RIGHT
Match each driver to the activity's actual cause. Setup costs → number of setups. Order processing → number of orders. The driver must explain why the cost exists.
Mistake 3: Implementing ABC but Ignoring the Results
❌ WRONG
Spending months building an ABC system, discovering catering is unprofitable, then continuing to price and promote it because "we've always done it that way."
✅ RIGHT
ABC is only valuable when it changes decisions: repricing, dropping products, restructuring service levels, or redesigning processes. The analysis is the easy part — acting on it is where value is created.
Key Takeaway
Activity-Based Costing assigns overhead by identifying the activities that cause costs, building cost pools for each activity, measuring the cost driver for each activity, and applying costs in proportion to each product's actual consumption of those activities. ABC eliminates the cost cross-subsidization that single-rate traditional costing creates — revealing that simple, high-volume products are often overcosted and complex, low-volume products are undercosted. The power of ABC is not changing the total overhead — it changes who it's charged to, producing a more accurate picture of product and customer profitability.
Test Your Understanding
Activity rates, overhead assignment, and cross-subsidization — check your answers below.
Question 1: Activity cost pool = $24,000. Total cost driver = 800 setups. Product A uses 150 setups. How much overhead is assigned to Product A?
Question 2: Under ABC, a low-volume complex product typically receives _______ overhead compared to traditional costing.
Ready to Practice?
Build activity pools, calculate rates, and assign overhead to products in the Practice Lab.
Try the Practice LabWhat's Next?
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Variable vs. Absorption Costing
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