Activity-based costing

In short

Activity-based costing (ABC) is an overhead costing method that first collects indirect costs into activity cost pools (setting up machines, handling materials, inspecting, processing orders) and then charges them to products using the cost driver that actually causes each activity. It was developed by Cooper and Kaplan in the late 1980s because traditional single-base absorption — one blanket rate on labour hours or machine hours — badly distorts product costs in modern factories where overheads are large and support work does not vary with volume. For a B.Com student it is a guaranteed Cost and Management Accounting question: definition, cost hierarchy, computation of activity cost driver rates, and the classic comparison statement showing traditional vs ABC unit cost. In practice ABC drives pricing, product-mix and outsourcing decisions in Indian manufacturing, banks, hospitals, telecom and shared-services centres, and is tested in interviews for cost analyst, FP&A, management-trainee and audit roles.

Explained

Why ABC arose — the failure of blanket absorption

• Traditional absorption charges overhead through one or two volume bases (direct labour hours, direct labour cost, machine hours, units). Fine when overhead is small and mostly volume-driven.
• Modern cost structure: direct labour has shrunk; overheads (set-ups, scheduling, quality, design, logistics, IT) have grown and are driven by diversity and complexity, not by volume.
• Result is cost cross-subsidisation: high-volume simple products absorb overhead they never caused and look dear; low-volume complex products look cheap. Management then prices wrongly, pushes the wrong product and drops a profitable line.
• ABC's logic: products consume activities; activities consume resources. So trace resources → activities → products.
• Terms: resource cost driver (basis for assigning a resource cost to an activity pool, e.g. floor area for rent) and activity cost driver (basis for assigning the pool to products, e.g. number of set-ups).
• CIMA definition in substance: an approach to costing that uses the cost of activities as the basis for assigning cost to outputs.

Building blocks and the cost hierarchy

• Activity – a unit of work with an identifiable purpose (machine set-up, purchase order, inspection, despatch).
• Cost pool – total cost accumulated for one activity for the period.
• Cost driver – the factor whose change causes the cost of the activity to change; must have a cause-and-effect link and be measurable.
• Cooper and Kaplan's four-level cost hierarchy:
  1. Unit-level – vary with each unit: power, consumables, direct machining. Drivers: units, machine hours, direct labour hours.
  2. Batch-level – incurred per batch regardless of batch size: set-up, first-article inspection, production scheduling, material movement. Drivers: number of set-ups, set-up hours, number of batches, number of material requisitions.
  3. Product-sustaining (product-level) – keep a product line alive: design, process engineering, BOM maintenance, specification updates, product-wise advertising. Drivers: number of design/engineering change notes, number of part numbers, number of products.
  4. Facility-sustaining (facility-level) – support the plant as a whole: factory rent, plant manager's salary, security, lighting, statutory compliance. No meaningful driver — Kaplan's advice is to keep them out of product cost and write them off against total contribution; Indian exam problems often still apportion them on floor area or machine hours, so follow the question's instruction.
• Some texts add a fifth level — customer-sustaining (customer calls, bespoke packing, credit control) — used in customer profitability analysis.
• Driver types: transaction drivers (number of set-ups, orders, inspections — cheapest, assumes equal effort per transaction), duration drivers (set-up hours, inspection minutes — more accurate), intensity/direct-charging drivers (actual resources charged to the job — most accurate, most costly).

Step-by-step procedure (exam method)

1. Identify the major activities in the organisation.
2. Identify the cost driver for each activity.
3. Create a cost pool for each activity and collect its overhead (assign general-ledger resource costs to pools using resource drivers).
4. Measure the total driver quantity for the period across all products.
5. Compute the activity cost driver rate = cost pool ÷ total driver quantity (e.g. ₹ per set-up, ₹ per order, ₹ per inspection).
6. Absorb into each product: driver units consumed by that product × rate.
7. Add prime cost: total cost ÷ output units = ABC unit cost.
8. Prepare a comparison/profitability statement against traditional cost and read off the decision.

Traditional absorption vs ABC

• Both are full/absorption costing systems — ABC changes *how* overhead is traced, not *whether* fixed cost is included. It is not marginal costing.
• ABC and marginal costing can coexist: ABC gives better long-run product cost; contribution analysis still governs short-run decisions.

Advantages, limitations and when ABC pays

Advantages

• More accurate product and service cost → better pricing, quoting and product-mix decisions.
• Shows cost of complexity — small batches, many variants, special orders — making SKU rationalisation visible.
• Identifies non-value-added activities (rework, excess movement, waiting) for elimination — the bridge to ABM.
• Supports customer, channel and distribution-cost analysis; helps make-or-buy and outsourcing decisions.
• Gives better data for budgeting (activity-based budgeting, which builds budgets from forecast activity volumes).

Limitations

• Expensive to install and maintain; needs time studies, driver counts and often ERP support.
• Driver selection is judgemental; a wrong driver gives confidently wrong numbers.
• Facility-level costs remain arbitrary — ABC does not solve them.
• Many costs are fixed in the short run, so "cost saved" by dropping a product may not actually leave the business (committed capacity).
• Historic/periodic data; unused-capacity cost inflates rates if actual rather than practical capacity is used as the denominator.
• Not accepted everywhere for statutory inventory valuation, so a parallel system may be needed.

ABC is worth it when: overheads are a high proportion of total cost, products differ a lot in volume and complexity, competition is intense and margins thin, and products have many support activities.

Activity-based management, TDABC and the Indian framework

• Activity-based management (ABM): using ABC information to act — operational ABM (do activities better/cheaper) and strategic ABM (choose which products, customers and channels to serve).
• Classify activities as value-added (customer would pay for it) and non-value-added (inspection, storage, movement, rework) and attack the latter.
• Time-driven ABC (TDABC) — Kaplan and Anderson, 2004: needs only two estimates per department — the cost per time unit of capacity (department cost ÷ practical capacity in minutes, usually 80–85% of theoretical) and the time required per transaction. It avoids employee interviews, scales in ERP, and exposes unused capacity cost explicitly.
• Indian framework: CAS 3 (Cost Accounting Standard on Production and Operation Overheads, ICMAI) requires overheads to be assigned on the basis of cause-and-effect or benefits received — language that admits activity-based assignment; CAS 1 classifies cost, CAS 4 covers cost of production for captive consumption.
• Section 148 of the Companies Act, 2013 with the Companies (Cost Records and Audit) Rules, 2014 makes cost records and cost audit mandatory for specified regulated and non-regulated industries above threshold turnover; firms maintaining CRA-1 records often use activity-based assignment inside them.
• Inventory valuation for financial statements follows AS 2 / Ind AS 2 (normal capacity absorption of fixed production overheads) — ABC output must be reconciled to this.
• Regulatory tariff setting (electricity, telecom, ports) uses activity/service-wise cost allocation in the same spirit.

Key points

• ABC – assigns overhead to products through activities and their cost drivers instead of one blanket volume rate.
• Core premise – products consume activities; activities consume resources.
• Cost pool – overhead accumulated for a single activity; cost driver – the causal factor; driver rate – pool ÷ driver volume.
• Resource cost driver vs activity cost driver – first moves GL cost into pools, second moves pools into products.
• Cost hierarchy – unit, batch, product-sustaining, facility-sustaining (plus customer-sustaining in some texts).
• Batch-level costs are the heart of ABC: per batch, not per unit, so small batches cost more per unit.
• Facility-level cost has no driver; ideally excluded from product cost and set against total contribution.
• Cross-subsidisation – traditional costing overcosts high-volume simple products and undercosts low-volume complex ones.
• Transaction, duration and intensity drivers – rising accuracy, rising cost of measurement.
• ABC is absorption costing, not marginal costing — all overhead is still charged to output.
• ABM – managing by activity: cut non-value-added work, re-price, re-mix.
• TDABC – cost per capacity minute × minutes per transaction; practical capacity ≈ 80–85% of theoretical; shows unused capacity.
• Use practical capacity as the denominator so idle capacity cost is not loaded onto products.
• Best suited to high-overhead, high-diversity, competitive businesses; wasteful where overhead is small or products uniform.
• CAS 3 (ICMAI) requires cause-and-effect overhead assignment; cost audit under Sec. 148, Companies Act 2013 + CRA Rules 2014.
• Service sector fit is strong — banks, insurers, hospitals, telecom, logistics, BPOs — where almost all cost is overhead.
• Limitation to quote – driver choice is judgemental and most overheads are fixed in the short run, so computed savings may not be realised.

Formulas and examples

Example 1 — Traditional vs ABC unit cost (classic exam problem)

A company makes two products. Overheads total ₹ 7,20,000.

Overhead pools: machine-related ₹ 2,40,000; set-up ₹ 2,40,000; purchasing ₹ 1,20,000; inspection ₹ 1,20,000.

*Traditional (machine-hour rate):* total machine hours = 20,000×2 + 4,000×2 = 40,000 + 8,000 = 48,000 hrs. Rate = 7,20,000 ÷ 48,000 = ₹ 15 per machine hour.

• A: 2 hrs × 15 = ₹ 30/unit → total cost ₹ 130/unit.
• B: 2 hrs × 15 = ₹ 30/unit → total cost ₹ 150/unit.

*ABC rates:*

• Machine-related: 2,40,000 ÷ 48,000 hrs = ₹ 5 per machine hour.
• Set-up: 2,40,000 ÷ 80 set-ups = ₹ 3,000 per set-up.
• Purchasing: 1,20,000 ÷ 200 orders = ₹ 600 per order.
• Inspection: 1,20,000 ÷ 120 inspections = ₹ 1,000 per inspection.

Check: 3,20,000 + 4,00,000 = 7,20,000 ✔. Reading: B, the low-volume product, consumes three-quarters of the set-ups, orders and inspections while making only 4,000 units — traditional costing shifted ₹ 2,80,000 of B's overhead onto A — ₹ 14 on each unit of A, understating B by ₹ 70 a unit.

Example 2 — Batch size and batch-level cost

Set-up cost ₹ 3,000 per set-up; one set-up per batch; machining ₹ 40 per unit.

A 100-unit special order costs ₹ 70/unit against ₹ 41/unit for a 3,000-unit run — the "cost of complexity" that ABC makes visible and that an average rate conceals.

Example 3 — Service sector: bank customer profitability

A branch's overheads: teller transactions ₹ 12,00,000 for 4,00,000 transactions; ATM servicing ₹ 6,00,000 for 10,00,000 ATM withdrawals; account maintenance ₹ 9,00,000 for 30,000 accounts; loan processing ₹ 10,00,000 for 2,000 applications.

Rates: teller = ₹ 3 per transaction; ATM = ₹ 0.60 per withdrawal; account = ₹ 30 per account p.a.; loan = ₹ 500 per application.

Customer X: 60 teller visits, 10 ATM withdrawals, 1 account, 1 loan application; income earned from X ₹ 450.

• Cost = 60×3 + 10×0.60 + 1×30 + 1×500 = 180 + 6 + 30 + 500 = ₹ 716 → loss ₹ 266.

Customer Y: 2 teller visits, 100 ATM withdrawals, 1 account, no loan; income ₹ 300.

• Cost = 2×3 + 100×0.60 + 30 = 6 + 60 + 30 = ₹ 96 → profit ₹ 204.

Decision: shift X's branch traffic to digital channels or re-price the loan; Y is the profitable profile — exactly why Indian banks price branch transactions beyond a free limit.

Example 4 — Time-driven ABC with unused capacity

Customer-service department cost ₹ 6,00,000 per month; 10 staff × 160 paid hours = 1,600 hours; practical capacity taken at 80% = 1,280 hours = 76,800 minutes.

• Capacity cost rate = 6,00,000 ÷ 76,800 = ₹ 7.8125 per minute.
• Time standards: process an order 8 min; handle a query 15 min; resolve a complaint 45 min.
• Volumes: 4,000 orders, 1,200 queries, 300 complaints → minutes used = 32,000 + 18,000 + 13,500 = 63,500 min.
• Cost assigned = 63,500 × 7.8125 = ₹ 4,96,093.75.
• Unused capacity = 76,800 − 63,500 = 13,300 min × 7.8125 = ₹ 1,03,906.25 (shown separately, not loaded on customers).
• Check: 4,96,093.75 + 1,03,906.25 = ₹ 6,00,000 ✔. Cost per order = 8 × 7.8125 = ₹ 62.50.

Example 5 — Decision: should the low-volume product be dropped?

From Example 1, B sells at ₹ 200 per unit.

• Traditional profit = 200 − 150 = ₹ 50/unit → ₹ 2,00,000.
• ABC profit = 200 − 220 = loss ₹ 20/unit → loss ₹ 80,000.
• But of B's ₹ 4,00,000 overhead, only avoidable activity cost leaves if B is dropped. If ₹ 3,00,000 (set-ups, orders, inspections, power) is avoidable and ₹ 1,00,000 is committed/facility cost, then dropping B loses revenue 4,000 × 200 = ₹ 8,00,000 and saves 4,000 × 120 (prime) + 3,00,000 = 4,80,000 + 3,00,000 = ₹ 7,80,000 → net worse by ₹ 20,000.
• Correct answer: do not drop blindly — raise price, increase batch size, or cut set-ups. ABC flags the problem; avoidability analysis makes the decision.

Where it is used

• Discrete manufacturing with many variants: auto components (Bosch, Sundram Fasteners, Motherson), pharma formulations with many SKUs and change-overs, specialty chemicals — set-up and quality-inspection drivers dominate.
• Banking, insurance and NBFCs: branch-transaction costing, cost-to-serve per account, channel costing (branch vs ATM vs UPI/app), claims-processing cost per policy.
• Hospitals and diagnostics (Apollo, Fortis, diagnostic chains) and CGHS/Ayushman Bharat package pricing: cost per OT hour, per bed-day, per test, per imaging slot.
• Telecom, logistics and e-commerce: cost per subscriber activation and per fault ticket; cost per pick, pack, line-haul km and per return (RTO) in warehousing.
• GCCs, IT and BPO shared services: cost per ticket, per invoice processed, per payroll record — the standard basis for internal chargeback and transfer pricing of support functions.
• Job roles: cost accountant and cost auditor (ICMAI), FP&A and pricing analyst, supply-chain/SKU rationalisation analyst, management consultant; also fed into cost records under CRA-1 and regulatory tariff filings.

Interview questions

• Q: What is activity-based costing in one line? A: A costing system that pools overheads by activity and charges them to products using the cost driver that causes each activity, instead of a single volume-based absorption rate.
• Q: Why does traditional costing distort product costs? A: It spreads all overhead on a volume base, so high-volume products absorb support costs caused by low-volume complex products — cross-subsidisation.
• Q: Difference between a cost pool and a cost driver? A: A cost pool is the money collected for one activity; the cost driver is the measurable factor that causes that cost to change and so divides the pool among products.
• Q: Give an example of each level of the cost hierarchy. A: Unit — power per machine hour; batch — machine set-up; product-sustaining — product design and BOM upkeep; facility-sustaining — factory rent and plant manager's salary.
• Q: How should facility-level costs be treated? A: Ideally kept out of product cost and set against total contribution, because there is no cause-and-effect driver; any apportionment is arbitrary.
• Q: Is ABC a substitute for marginal costing? A: No — ABC is a full-absorption method giving better long-run cost; short-run decisions still need contribution and avoidability analysis.
• Q: Why should practical capacity, not actual volume, be the denominator? A: Using actual volume loads the cost of idle capacity onto the products made, so unit costs rise when volumes fall — the death spiral; practical capacity keeps rates stable and shows unused capacity separately.
• Q: What is time-driven ABC and why was it developed? A: It replaces activity surveys with a capacity cost rate per minute and standard times per transaction, so it is cheaper to maintain, easier to update and reports unused capacity explicitly.
• Q: ABC says a product is loss-making — do you drop it? A: Not on that number alone; test which activity costs are actually avoidable, whether capacity is committed, and whether price, batch size or complexity can be changed first.
• Q: How would you apply ABC to a bank or a hospital? A: Build pools for transactions, account maintenance, claims or OT and bed-days, pick drivers like number of transactions, accounts, procedures or bed-days, and compute cost-to-serve per customer, product or channel.
• Q: Does Indian cost accounting regulation support ABC? A: Yes in substance — CAS 3 requires overheads to be assigned on cause-and-effect or benefit-received basis, and cost records under Section 148 of the Companies Act, 2013 with the CRA Rules, 2014 need activity-wise traceability; financial-statement inventory valuation still follows AS 2 / Ind AS 2.
• Q: When is ABC not worth implementing? A: When overheads are a small share of total cost, products are uniform in volume and complexity, or the cost of measuring drivers exceeds the value of the improved accuracy.

Common mistakes

• Dividing a batch-level pool by total units instead of the number of batches or set-ups — this silently rebuilds a volume rate and kills the whole point of the question.
• Forgetting to check that total overhead absorbed under ABC equals the total overhead given; an unreconciled total loses marks.
• Using the same driver for every pool, or picking a driver with no causal link (e.g. machine hours for purchasing).
• Treating ABC as marginal costing and reporting "contribution" where total cost was asked; or charging facility rent on set-ups.
• Recommending that a product be dropped straight from an ABC loss, without avoidable-cost and capacity analysis.
• Computing rates on actual rather than practical capacity, then blaming the product for idle-time cost.
• Mixing per-unit and total figures in the comparison statement — always state driver rates per driver unit and show overhead per unit separately.

Related topics

Cost accounting: elements of cost · Job, batch and contract costing · Marginal costing and break-even analysis · Budgeting and standard costing · Cost audit and cost records · Process costing