Ch 2: Overhead Absorption

Overhead absorption methods are essential accounting techniques that facilitate the allocation of indirect production costs, commonly referred to as overheads, to specific products or services. These methods are pivotal in ascertaining the actual cost of manufacturing a product, a fundamental component in pricing strategies, budgeting, and financial reporting. By meticulously distributing overhead costs across different cost centers or products using approaches such as "Blanket Overhead Absorption" or "Cost Centre Overhead Absorption," these methods empower businesses to make well-informed financial decisions, thereby enhancing their financial planning and competitive edge.

Overhead Absorption Methods Explained

Allocating overhead costs is a fundamental process for businesses aiming to understand their true production costs. Overhead absorption methods distribute indirect production expenses—like rent, utilities, and depreciation—across products or cost centers. These methods ensure accurate cost estimation, facilitating informed decision-making. Let’s dive into the intricacies of the absorption methods, their applications, challenges, and benefits.

Understanding Overhead Absorption Methods

1. Blanket Overhead Absorption

This straightforward approach uses a single absorption rate to allocate all production overhead costs without considering specific cost centers or their unique activities.

• Strengths:
• Limitations:

2. Cost Centre Overhead Absorption

This more sophisticated method calculates overhead costs for each cost center separately. Costs are allocated and apportioned based on their relevance to specific locations or activities.

• Process:
• Benefits:
• Example: Consider a manufacturing company producing two products:

This ensures each product’s costs accurately reflect its resource consumption.

Why Overhead Absorption is Essential

The primary goal of overhead absorption is to estimate product costs early in a period, as actual figures are unavailable until the period ends. By relying on budgeted figures, businesses can:

• Set competitive prices.
• Create realistic budgets.
• Evaluate financial performance throughout the period.

How Overhead Absorption Works

1. Budget Preparation:
2. Cost Allocation and Apportionment:
3. Reapportionment:
4. Determining the Absorption Rate:

Challenges in Overhead Absorption

While overhead absorption provides significant benefits, it is not without its challenges:

1. Variations in Actual Figures:
2. Selecting the Right Basis:

Non-Production Overheads

Non-production overheads, such as selling, administrative, and finance costs, are typically excluded from product costing. Instead, they are treated as expenses in the income statement. However, some businesses include these costs to gain a holistic view of total expenses, especially for profitability analysis.

Addressing Accuracy: A Practical Example

Scenario: A company budgets $100,000 for production overheads and expects 10,000 machine hours of activity.

• Step 1: Calculate the overhead absorption rate: Overhead Absorption Rate=Budgeted Overhead / Budgeted Activity Level =100,000/10,000=10 per machine hour.
• Step 2: Allocate overhead to products:

This ensures precise allocation based on actual resource usage.

Advantages of Overhead Absorption Methods

• Cost Accuracy: Reflects true costs by accounting for indirect expenses.
• Budgeting and Forecasting: Provides early cost estimates for planning and pricing.
• Resource Allocation: Highlights resource-intensive processes, aiding cost control.

Modern Considerations: The Role of Technology

With the rise of automation and ERP systems, businesses can now track overheads in real-time. These tools enable dynamic adjustments, reducing the likelihood of over or under-absorption.

Key takeaways

• Overhead absorption methods distribute indirect costs to products or cost centers, enhancing cost accuracy.
• Businesses can choose between Blanket Overhead Absorption (simple but less precise) and Cost Centre Absorption (more accurate but complex).
• Accurate cost allocation empowers businesses to make informed decisions about pricing, budgeting, and financial performance.
• While these methods enhance cost transparency, variations between budgeted and actual figures may lead to over or under-absorption.
• Financial analysts typically exclude non-production overheads from product costs but still consider them critical for financial analysis.

Time-Based Overhead Absorption is a method used in cost accounting to allocate indirect manufacturing costs (commonly referred to as overhead) to products based on the amount of time they spend in production. This approach recognizes that many overhead costs, such as rent, utilities, and machine power, are not directly tied to the number of units produced, but rather depend on the time a product or process occupies a particular production area. This concept is particularly valuable in situations where not all units produced are identical, making traditional unit-based absorption methods less suitable. Instead, time-based overhead absorption employs measures like labor hours or machine hours to distribute overhead costs, aligning more closely with the actual resource consumption of a product within a production cost center.

Time-Based Overhead Absorption

Time-based overhead absorption is a cost accounting method that allocates indirect manufacturing costs (overhead) based on the time products or processes spend in production, rather than the number of units produced. This approach is particularly useful in industries where overhead costs are closely tied to the duration of production activities.

How Time-Based Overhead Absorption Works

1. Selecting a Time Measure

Companies start by choosing a relevant time-based measure, such as labor hours or machine hours, to determine how much time each product or process spends in a production department. This measure serves as the foundation for distributing overhead costs.

2. Standard Time Allocation

Standard labor hours or machine hours are then allocated to each product. For instance:

• In labor-intensive manufacturing, standard labor hours reflect the time required for manual operations.
• In automated production settings, machine hours become the basis for absorption.

3. Calculating Overhead Rates

The overhead rate is calculated by dividing the total overhead costs by the chosen time measure. For example:

• If a company’s annual overhead costs amount to $200,000 and it expects to use 20,000 labor hours, the overhead rate per labor hour is:$200,000 / 20,000 hours = $10 per labor hour.

4. Allocating Overhead Costs

Overhead costs are assigned to products by multiplying the actual time spent in production by the overhead rate. This provides the overhead cost attributable to each product or process.

Example: Furniture Manufacturing

Imagine a furniture manufacturing company producing handcrafted wooden tables and assembled chairs. The company uses time-based overhead absorption to allocate costs.

• Production Details:
• Overhead Costs: Total annual overhead costs = $200,000; total labor hours = 20,000.
• Overhead Rate: $200,000 / 20,000 labor hours = $10 per labor hour.
• Cost Allocation:

This approach ensures that products consuming more time in production bear a proportionately higher share of the overhead costs, reflecting their actual resource usage.

Advantages of Time-Based Overhead Absorption

• Accuracy: Overheads like rent, utilities, and machine power are often time-dependent, making this method more precise than unit-based approaches.
• Resource Insight: Provides a clear view of resource consumption, aiding in better decision-making about pricing, profitability, and production.
• Flexibility: Adapts to various production environments, from labor-intensive to highly automated systems.

Challenges and Considerations

• Standard Time Accuracy: Determining accurate standard times requires careful analysis and can vary significantly across products or processes.
• Complexity in Mixed Environments: For companies with both labor-intensive and machine-intensive operations, selecting the appropriate measure (labor hours vs. machine hours) can be challenging.
• Dependency on Estimates: Overhead rate calculations rely on estimated total costs and time measures, which can lead to inaccuracies if projections are off.

Best Practices for Implementation

1. Analyze Resource Usage: Conduct time studies to establish accurate standard labor or machine hours for each product.
2. Reassess Regularly: Update overhead rates periodically to reflect changes in total costs or production volumes.
3. Integrate Technology: Use modern cost accounting software to streamline calculations and improve accuracy.

Comparing Time-Based Overhead Absorption to Other Methods

Activity-Based Costing (ABC)

While time-based absorption focuses on time, Activity-Based Costing considers various activities and their costs. ABC may offer more granularity but requires more data and analysis, making time-based absorption a simpler alternative for many companies.

Unit-Based Overhead Absorption

Traditional unit-based methods allocate costs based on the number of units produced. This can lead to distortions in resource allocation for products requiring significantly different production times, an issue resolved by time-based methods.

Conclusion

Time-based overhead absorption is a practical and effective cost allocation method, particularly for businesses with diverse production processes. By aligning costs with resource consumption, this approach promotes fair and accurate pricing strategies. Companies implementing this method should focus on maintaining accurate time measures and reassessing rates regularly to ensure continued reliability and effectiveness.

Key takeaways

• Time-based overhead absorption distributes indirect manufacturing costs based on the time products or processes spend in production.
• This method ensures fairness in cost allocation, reflecting the actual consumption of resources.
• By adopting time-based allocation, businesses can gain deeper insights into production costs and make informed decisions about pricing and resource management.

Learning objectives

By the end of this chapter you should be able to:

• Explain why service department costs are reapportioned and how this improves product costing and decision-making.
• Apply the direct method and the step-down method to transfer service department overheads to production departments.
• Calculate overhead absorption rates (OARs) and use them to absorb overheads based on activity.
• Identify over- and under-absorption of production overheads and prepare appropriate end-of-period adjustments.

Overview & key concepts

Accurate product costs require a fair share of indirect manufacturing costs (overheads). Overheads are first collected in cost centres. Some cost centres (production departments) make goods; others (service departments) support production but do not make saleable output. Since service departments exist to enable production, their costs must ultimately be charged to production departments so that product costs reflect the full cost of manufacturing.

This chapter covers:

• Reapportionment: transferring service department overheads to production departments using suitable allocation bases.
• Overhead absorption: charging production department overheads to output using an overhead absorption rate (OAR).
• Over/under absorption: reconciling absorbed overhead to the overhead actually incurred (and adjusting where appropriate).

Service departments and production departments

Service department

A service department is a cost centre that provides internal support to other departments. It does not normally produce goods for external customers. Examples include maintenance, stores, canteen, security, and production planning.

Production department

A production department is a cost centre where goods are manufactured or processed. Its costs are ultimately included in the cost of inventories and cost of sales through overhead absorption.

Reapportionment

What reapportionment achieves

Service department costs are initially recorded in their own cost centre totals. Reapportionment transfers these totals to production departments using an allocation base that reflects usage or benefit received.

A good allocation base should be:

• linked to the service provided (a sensible cost driver),
• measurable and reliable,
• consistently applied.

Typical bases include:

• Maintenance → machine hours, maintenance hours, number of service calls.
• Canteen → meals served, headcount, labour hours.

Core theory and frameworks

Reapportionment methods

Direct method

The direct method transfers each service department’s cost straight to production departments only. It ignores service-to-service support.

Use this method when:

• service departments provide little or no service to each other, or
• simplicity is prioritised over precision.

Mini-illustration (no numbers): If Maintenance supports Cutting, Finishing and the Canteen, the direct method allocates Maintenance costs only to Cutting and Finishing. Any Maintenance support provided to the Canteen is ignored for costing purposes.

Step-down method

The step-down method transfers service department costs in a sequence. Once a service department’s cost has been allocated out, it is “closed” and does not receive any further allocations.

This method recognises one-way service-to-service support (but not mutual, two-way support).

Choosing the sequence

If the question does not specify the order, a practical rule is:

• allocate first the service department that supports other service departments the most (largest inter-service support), or
• if service patterns are unclear, allocate first the service department with the largest overhead cost (materiality-driven order).

State the rule briefly and apply it consistently.

Overhead absorption rate (OAR)

Purpose

An OAR is used to charge production overheads to units based on activity. It supports consistent product costing and helps value inventories where applicable.

Calculation

OAR = Budgeted production overhead ÷ Budgeted activity level

Activity may be machine hours, labour hours, or units, depending on what best drives overhead in that department.

Absorbing overhead

Absorbed overhead = OAR × Actual activity

Over- and under-absorption

Definitions

• Over-absorption occurs when overhead absorbed exceeds overhead actually incurred.
• Under-absorption occurs when overhead absorbed is less than overhead actually incurred.

Differences arise because:

• actual activity differs from budget,
• actual overhead spending differs from budget,
• the chosen activity base is an imperfect driver.

End-of-period treatment

Common approaches:

1. Write off to cost of sales (often used when the variance is small and inventories are not material).
2. Prorate across work in progress, finished goods and cost of sales (used when inventories are significant, to avoid distortion).

Worked example

Narrative scenario

A manufacturing business operates two production departments—Cutting and Finishing—and two service departments—Maintenance and Canteen.

The following figures are budgeted overheads after initial allocation to cost centres:

• Cutting: £40,000
• Finishing: £30,000
• Maintenance: £12,000
• Canteen: £8,000

Budgeted service usage (expected usage) for reapportionment:

Maintenance (hours of repairs provided):

• Cutting: 300 hours
• Finishing: 200 hours
• Canteen: 100 hours

Canteen (meals served):

• Cutting: 600 meals
• Finishing: 400 meals
• Maintenance: 200 meals

The step-down method is used for reapportionment. The Canteen is allocated first, followed by Maintenance.

Budgeted production activity for OARs:

• Cutting budgeted machine hours: 10,400
• Finishing budgeted labour hours: 7,600

Actual production activity for the period:

• Cutting actual machine hours: 11,000
• Finishing actual labour hours: 8,000

Required

1. Reapportion Canteen and Maintenance costs to Cutting and Finishing using the step-down method.
2. Calculate the OARs for Cutting and Finishing.
3. Determine overhead absorbed using actual activity.
4. Identify any over- or under-absorption and prepare the adjustment required if the variance is written off to cost of sales.

Solution

Rounding policy

Monetary allocations are shown to the nearest penny. Final departmental totals are presented to the nearest pound where this improves readability.

1) Reapportionment using the step-down method

Step 1: Allocate Canteen cost (first in sequence)

Total meals served:

600 + 400 + 200 = 1,200

Allocate £8,000 based on meals:

• Cutting: 600/1,200 = 50% → £8,000 × 50% = £4,000.00
• Finishing: 400/1,200 = 33.333% → £8,000 × 33.333% = £2,666.67
• Maintenance: 200/1,200 = 16.667% → £8,000 × 16.667% = £1,333.33

Updated totals:

• Cutting: £40,000 + £4,000.00 = £44,000.00
• Finishing: £30,000 + £2,666.67 = £32,666.67
• Maintenance: £12,000 + £1,333.33 = £13,333.33
• Canteen: £8,000 allocated out → £0.00

Step 2: Allocate Maintenance cost (second in sequence)

Rule: Because Canteen is closed after Step 1, Maintenance is allocated only to Cutting and Finishing.

Maintenance hours to production departments:

300 + 200 = 500

Allocate £13,333.33 based on 300:200:

• Cutting: 300/500 = 60% → £13,333.33 × 60% = £8,000.00
• Finishing: 200/500 = 40% → £13,333.33 × 40% = £5,333.33

Final budgeted production department overheads (after reapportionment):

• Cutting: £44,000.00 + £8,000.00 = £52,000.00
• Finishing: £32,666.67 + £5,333.33 = £38,000.00

Check:

Total budgeted overheads initially = £40,000 + £30,000 + £12,000 + £8,000 = £90,000 Final budgeted production overheads = £52,000 + £38,000 = £90,000 ✔

2) Calculate OARs

The departmental totals after reapportionment are treated as budgeted production overheads used to set predetermined OARs.

• Cutting OAR: £52,000 / 10,400 = £5.00 per machine hour
• Finishing OAR: £38,000 / 7,600 = £5.00 per labour hour

3) Absorb overhead using actual activity

Absorbed overhead:

• Cutting: £5.00 × 11,000 = £55,000
• Finishing: £5.00 × 8,000 = £40,000

4) Over/under absorption and adjustment

Note on budget vs actual (for this illustration)

To keep the focus on the absorption mechanism, assume that actual overhead incurred equals the budgeted overhead totals after reapportionment (Cutting £52,000; Finishing £38,000). Therefore, any over/under absorption arises only because actual activity differs from budgeted activity.

Compare absorbed vs actual overhead:

• Cutting: absorbed £55,000 vs actual £52,000 → over-absorbed £3,000
• Finishing: absorbed £40,000 vs actual £38,000 → over-absorbed £2,000

Total over-absorption = £5,000.

Adjustment (variance written off to cost of sales)

In a control-account system, overhead is accumulated in an overhead control account and overhead absorbed is posted during the period using the OAR. The end-of-period entry below clears the remaining balance by writing the variance to cost of sales.

Over-absorption means cost of sales has been charged with too much overhead. Writing it off reduces cost of sales and increases profit.

Journal entry (combined):

• Dr Overhead control account £5,000
• Cr Cost of sales £5,000

(Separate departmental entries are also acceptable.)

Interpretation of the results

Reapportionment ensures that support costs from service departments are included within production department overhead totals, improving the completeness of product costs.

The OARs convert departmental overheads into a cost per unit of activity. Because actual activity exceeded budget in both departments, overhead absorbed exceeded overhead incurred (given the simplifying assumption that actual overhead equals budget). The resulting over-absorption is adjusted so that cost of sales reflects the period’s overhead cost more appropriately.

What often goes wrong in exam answers

• Wrong recipients in the step-down method: once a service cost centre is closed, it must not receive further allocations—so the denominator changes as the sequence progresses.
• Sequence not justified: if the order is not stated, apply a clear rule (allocate first from the service department that supports other service departments the most, or the one with the largest cost if patterns are unclear).
• Weak cost driver: choosing a base that does not reflect consumption makes the allocation hard to defend (e.g., allocating maintenance by floor area without a clear link).
• Mixing budget and actual in the OAR: the rate is normally set in advance using budget/normal activity, then applied to actual activity.
• Variance sign errors: when writing off to cost of sales, over-absorption reduces cost of sales; under-absorption increases it.
• Ignoring inventory significance: if inventories are material, writing the whole variance to cost of sales may distort profit; proration may be more appropriate.

Extension: reciprocal service allocations (beyond this chapter)

Where service departments provide significant support to each other in both directions, the step-down method can understate mutual service effects. In such cases, a reciprocal approach can be used (for example, repeated distribution or simultaneous equations) to share service costs more fully before charging them to production departments. This is usually required only when explicitly stated.

Summary

• Service department costs are transferred to production departments so product costs include a fair share of total manufacturing overhead.
• The direct method is simpler but ignores service-to-service support.
• The step-down method allocates service department costs in sequence and captures one-way inter-service support; the order chosen can affect results.
• OARs are predetermined using budgeted overhead and budgeted activity, then applied to actual activity to absorb overhead.
• Differences between absorbed and actual overhead create over- or under-absorption, which is adjusted—often by writing off to cost of sales or by proration when inventories are significant.

Quick recap (bullet form)

• Reapportion service costs → production departments
• Compute OARs → budgeted overhead ÷ budgeted activity
• Absorb overhead → OAR × actual activity
• Compare absorbed vs actual → over/under absorption
• Adjust → clear variance to cost of sales (or prorate)

FAQ

What is the key difference between the direct and step-down methods?

The direct method sends each service department’s cost straight to production departments only, so any support exchanged between service departments is left out. The step-down method transfers costs out in an order, so earlier service departments can pass some cost to later ones—but not the other way around once a department has been closed.

How do you choose an allocation base?

Choose a base that best reflects consumption of the service. For example, meals served (or headcount) is usually suitable for canteen costs, while machine hours (or maintenance hours) is often suitable for maintenance costs.

Why does the step-down sequence matter?

Because once a service department is allocated out, it is closed and cannot receive further allocations. If later departments also support earlier ones, that support is ignored, so the chosen order can change the final production department overhead totals.

What causes over- and under-absorption?

Over/under absorption arises when actual activity or actual overhead differs from budget, or when the activity base does not closely track overhead behaviour.

How do adjustments affect profit?

If written off to cost of sales:

• Over-absorption reduces cost of sales and increases profit.
• Under-absorption increases cost of sales and reduces profit.

Glossary

Absorbed overhead Overhead charged to production based on an absorption rate and actual activity.

Allocation base A measurable driver used to distribute overheads, intended to reflect usage or benefit received.

Direct method A reapportionment approach that transfers service department costs directly to production departments only.

Over-absorption A situation where overhead absorbed is greater than overhead actually incurred.

Overhead absorption rate (OAR) A predetermined rate used to charge overhead to output, typically budgeted overhead divided by budgeted activity.

Production department A cost centre that manufactures or processes goods; its costs are included in product costs.

Reapportionment The transfer of service department overheads to production departments using appropriate allocation bases.

Service department A cost centre that supports production activities but does not itself produce saleable output.

Step-down method A sequential allocation approach where service department costs are transferred out one department at a time. After a service department is allocated, it is closed, so later allocations cannot flow back into it. This captures only one-direction inter-service support.

Under-absorption A situation where overhead absorbed is less than overhead actually incurred.

Learning objectives

By the end of this chapter you will be able to:

• Calculate a full unit production cost using overhead absorption rates (OARs).
• Distinguish between allocation and apportionment of overheads to cost centres and apply suitable apportionment bases.
• Select appropriate absorption bases (labour hours, machine hours, or units) in line with the main driver of overhead consumption.
• Apply departmental OARs to products and interpret the results for pricing, margin analysis, and inventory valuation.
• Identify common exam-style errors in absorption costing and correct them, including base selection, rounding, and treatment of under/over absorption.

Overview & key concepts

Absorption costing is a product costing method that includes all production costs in the cost of each unit produced. It brings together:

• Direct production costs (direct materials, direct labour, and other direct production costs where relevant), and
• A share of production overheads (indirect production costs such as factory rent, production supervisors, depreciation of production equipment, and factory power).

Because overheads are not traceable to individual units, they are collected into cost centres and then absorbed into products using an activity measure that reflects how resources are consumed.

Absorption costing and financial statements

In absorption costing, production costs follow the physical flow of goods:

• When units are produced but not yet sold, their production cost is held in inventory (an asset).
• When units are sold, their production cost is released to cost of sales (an expense).

A quick illustration:

• If a unit costs £60 to produce and remains unsold at the reporting date, the £60 remains in inventory.
• If it is sold next period, the £60 moves from inventory to cost of sales in that later period.

Fixed production overhead and normal capacity

Fixed production overhead (for example, factory rent) is spread over activity. For inventory valuation, fixed production overhead is normally absorbed using a normal/expected capacity level. This avoids inventory values being distorted by unusual changes in production volume.

If production is abnormally low, some fixed production overhead may remain unabsorbed. That unabsorbed amount is treated as a period expense rather than being carried forward in inventory.

Core theory and frameworks

1) Cost units and cost centres

• A cost unit is the item you want to cost (for example, one unit of Product A).
• A cost centre is a department or function where costs are accumulated (for example, Machining or Assembly).

Cost centres are commonly classified as:

• Production cost centres: directly involved in manufacturing (for example, Machining).
• Service cost centres: support production (for example, maintenance, stores, canteen).

Overheads are first assigned to cost centres and then absorbed into products.

2) Production costs vs non-production costs

For absorption costing, keep the boundary clear:

Included in unit production cost

• Direct materials and direct labour
• Production overheads (variable and fixed) related to manufacturing activity

Not included in unit production cost

• Selling and distribution costs
• Head office administration and general management costs unrelated to manufacturing
• Finance costs (for example, interest)

Common classification trap: Factory administration that supports production (for example, production planning staff based in the factory) is usually treated as production overhead, whereas head office administration is not.

3) Allocation vs apportionment

Overheads are assigned to cost centres in two main ways:

Allocation (100% to one centre) Used when the overhead clearly belongs to a single cost centre. Example: a supervisor dedicated solely to Machining.

Apportionment (shared across centres) Used when an overhead benefits more than one cost centre and must be split using a rational basis. Examples of apportionment bases:

• Rent/rates → floor area
• Machine power → machine hours
• Indirect materials handling → direct materials value (where appropriate)

A strong basis reflects cause and effect: it should mirror how the overhead is consumed.

4) Overhead absorption rate (OAR)

An OAR converts budgeted overhead into a rate per unit of activity:

OAR = Budgeted production overhead ÷ Budgeted activity level

The rate must be stated with its base (for example, £ per machine hour).

Common activity measures:

• Machine hours (often best where machinery drives overhead)
• Labour hours (often best where labour effort drives overhead)
• Units (only sensible for homogeneous output where overhead consumption per unit is broadly similar)

OARs are commonly set using budgeted figures to provide a stable predetermined rate for planning and consistent product costing.

5) Absorbing overheads into products

Once an OAR is calculated, absorbed overhead is found by:

Absorbed overhead = OAR × Activity used

With departmental rates, the product absorbs overhead separately for each department, using that department’s chosen base.

6) Under- and over-absorption in practice

A predetermined rate will rarely equal actual overhead incurred exactly, so a difference arises:

• Under-absorption: absorbed overhead is less than actual overhead incurred
• Over-absorption: absorbed overhead is greater than actual overhead incurred

Typical treatments (high-level):

• Costing/management reporting: if the difference is immaterial, it may be written off to the profit statement (often through cost of sales). If material, it can be shared across work in progress, finished goods, and cost of sales to avoid distorting closing inventory and cost of sales.
• Inventory valuation focus: the aim is reasonable overhead absorption (including fixed overhead at normal capacity). Unabsorbed fixed overhead arising from abnormally low production is treated as a period expense rather than carried in inventory.

Worked example

Narrative scenario

A manufacturing company produces two products: Product A and Product B. Production takes place in two production departments: Machining and Assembly.

Budgeted monthly production overheads:

• Factory rent: £12,000, apportioned by floor area
• Factory power: £9,000, apportioned by machine hours
• Indirect materials: £3,000, apportioned by direct materials cost
• Department supervisor (Machining only): £2,000, allocated to Machining

Department data:

• Machining: 600 m²; 1,500 machine hours; £24,000 direct materials; 600 labour hours
• Assembly: 400 m²; 500 machine hours; £36,000 direct materials; 1,400 labour hours

Product data (per unit):

• Product A: 0.8 machining machine hours; 1.5 assembly labour hours; direct materials £18; direct labour £22
• Product B: 1.2 machining machine hours; 0.5 assembly labour hours; direct materials £20; direct labour £25

The company uses departmental OARs.

Required

1. Allocate and apportion overheads to each department.
2. Calculate the OAR for each department.
3. Calculate absorbed overhead per unit for each product.
4. Compute the full production cost per unit for each product.
5. Interpret the results for pricing/margins and inventory valuation.

Solution

Step 1: Allocate and apportion overheads to departments

(a) Rent £12,000 apportioned by floor area

Total area = 600 + 400 = 1,000 m²

• Machining: £12,000 × 600/1,000 = £7,200
• Assembly: £12,000 × 400/1,000 = £4,800

(b) Power £9,000 apportioned by machine hours

Total machine hours = 1,500 + 500 = 2,000 hours

• Machining: £9,000 × 1,500/2,000 = £6,750
• Assembly: £9,000 × 500/2,000 = £2,250

(c) Indirect materials £3,000 apportioned by direct materials cost

Total direct materials = £24,000 + £36,000 = £60,000

• Machining: £3,000 × 24,000/60,000 = £1,200
• Assembly: £3,000 × 36,000/60,000 = £1,800

(d) Supervisor £2,000 allocated to Machining

• Machining: £2,000
• Assembly: £0

Department overhead totals

• Machining: £7,200 + £6,750 + £1,200 + £2,000 = £17,150
• Assembly: £4,800 + £2,250 + £1,800 = £8,850

Step 1 mini-summary

Step 2: Calculate departmental OARs

State the rate clearly with its base.

Machining OAR (per machine hour)

Machining OAR = £17,150 ÷ 1,500 = £11.4333… per machine hour (Use £11.4333… in workings; round for presentation.)

Assembly OAR (per labour hour)

Assembly OAR = £8,850 ÷ 1,400 = £6.3214… per labour hour

Step 3: Absorb overheads into products (per unit)

Product A

• Machining: 0.8 machine hours × £11.4333… = £9.15
• Assembly: 1.5 labour hours × £6.3214… = £9.48

Total absorbed overhead (A) = £18.63

Product B

• Machining: 1.2 machine hours × £11.4333… = £13.72
• Assembly: 0.5 labour hours × £6.3214… = £3.16

Total absorbed overhead (B) = £16.88

Step 4: Full production cost per unit

Product A

• Direct materials: £18.00
• Direct labour: £22.00
• Absorbed production overhead: £18.63

Full production cost per unit (A) = £58.63

Product B

• Direct materials: £20.00
• Direct labour: £25.00
• Absorbed production overhead: £16.88

Full production cost per unit (B) = £61.88

Step 5: Interpretation

Pricing and margin analysis (managerial use)

• Product B is costlier mainly because it uses more Machining time, and Machining has a high overhead rate per machine hour.
• Departmental rates help avoid miscosting when departments consume overheads differently. A single blanket rate could distort product margins.

Inventory valuation and cost of sales (financial reporting use)

• These unit costs support inventory valuation for units still on hand and cost of sales for units sold.
• Fixed production overhead is spread using an expected activity level (normal capacity). Any fixed overhead not absorbed due to abnormally low production is treated as a period expense rather than being carried in inventory.

Common pitfalls and misunderstandings

• Not stating the base with the OAR: Always present the rate as “£ per machine hour” or “£ per labour hour” and keep it consistent.
• Weak absorption base selection: Choose the base that best reflects how the overhead is driven (machine-driven vs labour-driven).
• Rounding too early: Keep several decimals for OARs and absorbed overhead; round at the final answer.
• Mixing allocation and apportionment: Allocation is a full charge to one centre; apportionment is a split using a basis.
• Including non-production costs in unit costs: Selling, distribution, head office admin, and finance costs are not part of production cost.
• Using units as a base in unsuitable situations: Units are only sensible for broadly homogeneous output and similar overhead consumption per unit.
• Ignoring service cost centres: When service departments exist, their costs are commonly reapportioned to production departments before calculating OARs. Questions may require methods such as step-down (sequential), repeated distribution, or reciprocal approaches.
• Forgetting normal capacity logic for fixed overhead: Do not let abnormally low production inflate unit costs and inventory values.

Summary and further reading

Absorption costing produces a full unit production cost by adding absorbed production overheads to direct production costs. The typical sequence is:

1. Collect overheads into cost centres.
2. Allocate and apportion overheads to production departments (and reapportion service department costs where required).
3. Select suitable activity bases and calculate departmental OARs using budgeted overhead and budgeted activity.
4. Absorb overheads into products using the activity consumed.
5. Use full production costs to value inventory and cost of sales, remembering that fixed production overhead absorption is based on normal capacity and abnormal unabsorbed amounts are expensed.

For wider context, read around inventory valuation, production vs non-production cost classification, and how predetermined rates support planning and control.

FAQ

What is the main purpose of absorption costing?

To calculate a full production cost per unit by including production overheads within unit costs. This supports inventory valuation, margin analysis, and pricing decisions where a full cost is required.

How do you choose an absorption base?

Choose an activity measure that best reflects how overheads are consumed in that cost centre. Machine hours usually suit machine-driven overheads; labour hours suit labour-driven overheads. Units are only appropriate where output is homogeneous and overhead consumption per unit is similar.

Why are OARs commonly based on budgeted figures?

Budgeted overhead and budgeted activity provide a stable predetermined rate for consistent costing and planning. Actual outcomes are then compared against absorbed overhead to identify under- or over-absorption.

What are frequent calculation errors?

Early rounding, mixing bases (labour vs machine), incorrect apportionment totals, and mistakenly including non-production overheads in unit costs.

How does absorption costing affect reported profit?

If production and sales volumes differ, some production overhead (especially fixed overhead) may be carried in inventory rather than expensed immediately. This can shift reported profit between periods even if cash flows do not change.

What is the difference between allocation and apportionment?

Allocation charges an overhead fully to one cost centre because it clearly belongs there. Apportionment splits a shared overhead between cost centres using a rational basis.

Why can absorption costing be less useful for some short-term decisions?

Because it spreads fixed production overhead across units, it may not represent the incremental cost of a one-off decision. Short-term decisions often require focus on costs that change as a result of the decision (typically variable and avoidable costs).

Glossary

Absorption costing A costing approach that includes direct production costs and an absorbed share of production overheads in the cost of each unit produced.

Overhead (production overhead) An indirect production cost that cannot be traced economically to a single unit, such as factory rent, production supervisors, or factory utilities.

Cost centre A department or function where costs are collected for costing and control purposes.

Production cost centre A cost centre directly involved in manufacturing goods or delivering the service output.

Service cost centre A support cost centre that provides services to production cost centres (for example, maintenance or stores).

Allocation Charging an overhead in full to one cost centre when it clearly relates to that centre.

Apportionment Splitting a shared overhead between cost centres using a rational basis (for example, floor area or machine hours).

Overhead absorption rate (OAR) A predetermined rate used to absorb production overhead into products, calculated as budgeted production overhead divided by budgeted activity.

Absorption base The activity measure used to absorb overhead, such as machine hours, labour hours, or units.

Cost unit The item being costed, such as one unit of a product.

Full production cost Direct materials + direct labour (and other direct production costs where relevant) + absorbed production overheads.

Under-absorption / over-absorption The difference between actual production overhead incurred and overhead absorbed using predetermined rates. Under-absorption arises when absorbed overhead is lower than actual; over-absorption is the opposite.

Normal capacity (normal production level) An expected level of activity used to absorb fixed production overhead so that inventory valuation is not distorted by unusual volume changes.