DECISION MAKING TECHNIQUES: RELEVANT COST ANALYSIS – COMPLETE GUIDE WITH EXAMPLES AND CALCULATIONS
Every business decision involves costs. But not all costs are relevant. Some costs matter for decision-making. Others do not. Understanding the difference is essential for making good decisions. Relevant cost analysis helps you identify which costs should influence your decisions and which should be ignored.
Get this wrong, and you will make poor decisions, overpay for products, and miss opportunities. Get it right, and you unlock the ability to make informed, cost-effective decisions that drive profitability. This guide breaks down everything: the concept of relevant costs, how to identify them, practical applications, and step-by-step calculations. Let us get into it.
The Pain Points: Why Businesses Struggle with Relevant Cost Analysis
Confusing Sunk Costs with Relevant Costs
Many business leaders struggle to ignore sunk costs. Sunk costs are costs that have already been incurred and cannot be recovered. They should not influence future decisions. But human psychology makes it hard to let go. Leaders feel they have invested too much to walk away. This is the sunk cost fallacy. It leads to poor decisions, wasted resources, and missed opportunities.
Consider a business that has spent N10 million developing a new product. The product is not performing well. The business should discontinue it. But the leaders feel they cannot walk away because they have already invested N10 million. This is the sunk cost fallacy. The N10 million is gone. It should not influence the decision to continue or discontinue the product.
Another common example is a business that continues to invest in an underperforming project because it has already spent money on it. This is like throwing good money after bad. The rational decision is to cut losses and move on. But human emotions make this difficult. The fear of admitting failure and the desire to avoid regret drive poor decisions.
Including Allocated Fixed Costs
Many businesses make the mistake of including allocated fixed costs in decision-making. These are fixed costs that are allocated to different products or departments. They are not incremental costs. They do not change with the decision. Including them can lead to incorrect decisions.
For example, a business may allocate a portion of head office rent to each product line. If the business is considering discontinuing a product, the allocated rent should not be included. The rent will still be paid regardless of the decision. Including it makes the product appear less profitable than it really is.
Similarly, depreciation on existing equipment is often included in decision-making. But depreciation is a non-cash expense that reflects the allocation of past costs. It does not change with the decision. It should be ignored.
Overlooking Opportunity Costs
Opportunity costs are the benefits foregone by choosing one alternative over another. They are often overlooked in decision-making. But they are real costs that should be considered. Failing to consider opportunity costs leads to suboptimal decisions.
For example, a business owns a building that it could rent out for N5 million per year. If it uses the building for its own operations, the opportunity cost is N5 million. This should be included in the decision-making process.
Another example is the use of employees’ time. If employees are used for one project, they cannot work on another. The value of the foregone project is an opportunity cost. This is often overlooked because it does not appear in the accounting records.
The Cost of Getting It Wrong
A manufacturing company in Lagos considered outsourcing production. It compared the variable cost of production with the supplier’s price. It concluded that outsourcing was cheaper. But it forgot to consider the opportunity cost of freeing up factory space. It could have used the space to produce a more profitable product. The decision to outsource was suboptimal. The cost of getting it wrong was significant.
Another business in Abuja used relevant cost analysis correctly. It identified all relevant costs, ignored sunk costs, and considered opportunity costs. It made a decision that improved profitability by 15%. The difference was clear. The business that got it right was more profitable and more competitive.
A retail business in Port Harcourt continued to stock a product line that was underperforming. It focused on the sunk costs of inventory and marketing. It ignored the relevant costs and opportunity costs. The result was continued losses and wasted resources. The lesson is clear: relevant cost analysis is essential for good decision-making.
What Is Relevant Cost Analysis?
Definition
Relevant cost analysis is a decision-making technique that focuses on costs that differ between alternatives. It helps decision-makers identify which costs should be considered and which should be ignored. The goal is to make decisions based on the incremental costs and benefits of each alternative.
This technique is widely used in management accounting and financial analysis. It is a practical tool for evaluating decisions in a systematic and objective way. By focusing on relevant costs, businesses can avoid common pitfalls and make better decisions.
The Core Principle
The core principle of relevant cost analysis is simple: Only costs that differ between alternatives are relevant. Costs that are the same under all alternatives are irrelevant. They should be ignored in the decision-making process.
This principle is based on the idea that decision-making is about comparing alternatives. If a cost is the same under all alternatives, it does not affect the decision. It is a common factor that cancels out. Only costs that differ between alternatives matter. They are the costs that should influence the decision.
Why Relevant Cost Analysis Matters
Relevant cost analysis is essential for:
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Make or buy decisions: Should you produce a component in-house or buy it from a supplier?
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Pricing decisions: Should you accept a special order at a lower price?
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Product mix decisions: Which products should you focus on?
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Discontinuation decisions: Should you discontinue a product or service?
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Special order decisions: Should you accept a one-time order at a reduced price?
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Outsourcing decisions: Should you outsource a function or keep it in-house?
It helps businesses make informed decisions based on incremental costs and benefits. Without relevant cost analysis, businesses risk making decisions that seem logical but are actually suboptimal.
Key Concepts in Relevant Cost Analysis
Relevant Costs
Definition: Relevant costs are costs that differ between alternatives. They are future costs that will change depending on the decision.
Characteristics:
They are future costs (not past costs)
They differ between alternatives
They are avoidable (can be eliminated by choosing a different alternative)
Examples:
Direct materials that are specific to a product
Direct labour that can be redeployed
Variable overheads that change with production
Opportunity costs
Irrelevant Costs
Definition: Irrelevant costs are costs that do not differ between alternatives. They are the same regardless of the decision.
Characteristics:
They are past costs (sunk costs)
They do not differ between alternatives
They are unavoidable (will be incurred regardless of the decision)
Examples:
Sunk costs (past expenditures)
Allocated fixed costs
Depreciation on existing assets
Costs that are the same under all alternatives
Sunk Costs
Definition: Sunk costs are costs that have already been incurred and cannot be recovered. They are always irrelevant for decision-making.
Key Rule: Ignore sunk costs. They are gone. They cannot be changed by any future decision.
Examples:
Past research and development costs
Money spent on failed projects
Depreciation on equipment already purchased
Opportunity Costs
Definition: Opportunity costs are the benefits foregone by choosing one alternative over another. They are relevant costs that should be included in decision-making.
Key Rule: Include opportunity costs. They represent the value of the next best alternative.
Examples:
Lost rent from using a building for internal operations
Lost profit from not producing a more profitable product
Lost interest from using cash for investment rather than saving
Differential Costs
Definition: Differential costs are the difference in total costs between two alternatives. They are the net relevant costs of a decision.
Key Rule: Calculate the differential cost to determine which alternative is better.
Examples:
Difference between making a product in-house and outsourcing it
Difference between accepting and rejecting a special order
Difference between continuing and discontinuing a product line
Identifying Relevant Costs: Step-by-Step Guide
Step 1: Identify the Decision
Clearly define the decision you are making. What are the alternatives? What are the objectives? This step is crucial because it sets the scope of the analysis. Without a clear definition of the decision, the analysis will be unfocused and unhelpful.
Step 2: Identify All Costs
List all costs associated with each alternative. This includes direct costs, indirect costs, and opportunity costs. Be thorough. Include every cost that could potentially be affected by the decision. This step ensures that no relevant costs are overlooked.
Step 3: Eliminate Sunk Costs
Remove all sunk costs. They are gone. They cannot influence the decision. This is often the hardest step because of human psychology. But it is essential for making rational decisions.
Step 4: Eliminate Costs That Do Not Differ
Remove all costs that are the same under all alternatives. They are irrelevant. This step simplifies the analysis and focuses attention on the costs that matter.
Step 5: Identify Differential Costs
The remaining costs are the relevant costs. They are the costs that differ between alternatives. These are the costs that should influence the decision.
Step 6: Compare Alternatives
Compare the relevant costs of each alternative. Choose the alternative with the lowest relevant cost or highest net benefit. This step involves both quantitative and qualitative analysis.
Practical Applications with Worked Examples
Example 1: Make or Buy Decision
Scenario:
A manufacturing company is deciding whether to make a component in-house or buy it from a supplier.
| Cost Item | Make (N) | Buy (N) |
|---|---|---|
| Direct Materials | 200,000 | – |
| Direct Labour | 150,000 | – |
| Variable Overhead | 100,000 | – |
| Fixed Overhead (Allocated) | 80,000 | 80,000 |
| Purchase Price | – | 400,000 |
| Total Cost | 530,000 | 480,000 |
Step 1: Identify Relevant Costs
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Direct Materials: N200,000 (Relevant – differs)
-
Direct Labour: N150,000 (Relevant – differs)
-
Variable Overhead: N100,000 (Relevant – differs)
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Fixed Overhead: N80,000 (Irrelevant – same under both alternatives)
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Purchase Price: N400,000 (Relevant – differs)
Step 2: Compare Relevant Costs
| Cost Item | Make (N) | Buy (N) |
|---|---|---|
| Direct Materials | 200,000 | – |
| Direct Labour | 150,000 | – |
| Variable Overhead | 100,000 | – |
| Purchase Price | – | 400,000 |
| Total Relevant Cost | 450,000 | 400,000 |
Decision: The relevant cost of buying (N400,000) is lower than making (N450,000). The company should buy the component.
Example 2: Special Order Decision
Scenario:
A company receives a special order for 1,000 units at a price of N800 per unit. Current production is 5,000 units. Normal selling price is N1,000 per unit.
| Cost Item | Per Unit (N) |
|---|---|
| Direct Materials | 300 |
| Direct Labour | 200 |
| Variable Overhead | 100 |
| Fixed Overhead (Allocated) | 150 |
| Selling and Admin (Variable) | 50 |
Step 1: Identify Relevant Costs
Direct Materials: N300 (Relevant – incremental)
Direct Labour: N200 (Relevant – incremental)
Variable Overhead: N100 (Relevant – incremental)
Fixed Overhead: N150 (Irrelevant – same regardless of order)
Selling and Admin (Variable): N50 (Relevant – incremental)
Step 2: Calculate Relevant Cost per Unit
Relevant Cost = N300 + N200 + N100 + N50 = N650
Step 3: Compare Price to Relevant Cost
Price per unit: N800
Relevant Cost per unit: N650
Decision: The special order contributes N150 per unit (N800 – N650). The company should accept the order, assuming it has spare capacity.
Example 3: Discontinuation Decision
Scenario:
A company is considering discontinuing Product C. Data for three products:
| Item | Product A | Product B | Product C | Total |
|---|---|---|---|---|
| Sales | 500,000 | 400,000 | 300,000 | 1,200,000 |
| Variable Costs | 300,000 | 250,000 | 200,000 | 750,000 |
| Contribution Margin | 200,000 | 150,000 | 100,000 | 450,000 |
| Fixed Costs (Allocated) | 80,000 | 70,000 | 60,000 | 210,000 |
| Net Profit | 120,000 | 80,000 | 40,000 | 240,000 |
Step 1: Identify Relevant Costs
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If Product C is discontinued:
Sales lost: N300,000
Variable costs saved: N200,000
Fixed costs saved: N0 (allocated fixed costs will continue)
Contribution lost: N100,000
Step 2: Compare Alternatives
| Item | Continue | Discontinue |
|---|---|---|
| Contribution Margin | 100,000 | – |
| Fixed Costs | 60,000 | 60,000 |
| Net Profit | 40,000 | (60,000) |
Decision: The company should continue Product C. Discontinuing it would reduce overall profit by N100,000 (the lost contribution margin) with no fixed cost savings.
Example 4: Product Mix Decision
Scenario:
A company has limited machine hours. It can produce two products:
| Item | Product X | Product Y |
|---|---|---|
| Selling Price | 500 | 400 |
| Variable Cost | 300 | 200 |
| Contribution Margin | 200 | 200 |
| Machine Hours Required | 4 | 2 |
| Contribution per Machine Hour | 50 | 100 |
Step 1: Calculate Contribution per Machine Hour
Product X: N200 ÷ 4 hours = N50 per hour
Product Y: N200 ÷ 2 hours = N100 per hour
Step 2: Decision
Product Y has a higher contribution per machine hour (N100 vs N50). The company should prioritise Product Y.
Example 5: Outsourcing with Opportunity Cost
Scenario:
A company can produce a component in-house for N500,000 or buy it for N400,000. If the company buys the component, the factory space can be rented out for N150,000 per year.
Step 1: Calculate Relevant Costs
Make: N500,000
Buy: N400,000 + Opportunity Cost (N150,000) = N550,000
Step 2: Compare Alternatives
| Item | Make | Buy |
|---|---|---|
| Direct Cost | 500,000 | 400,000 |
| Opportunity Cost | – | 150,000 |
| Total Relevant Cost | 500,000 | 550,000 |
Decision: The company should continue making the component in-house (N500,000 vs N550,000). The opportunity cost of renting out the space makes buying more expensive.
Common Mistakes to Avoid
Mistake 1: Including Sunk Costs
Problem: Including costs that have already been incurred and cannot be recovered.
Solution: Identify and eliminate all sunk costs. They are irrelevant.
Mistake 2: Including Allocated Fixed Costs
Problem: Including fixed costs that are allocated to products or departments.
Solution: Only include costs that change with the decision. Allocated fixed costs are irrelevant.
Mistake 3: Overlooking Opportunity Costs
Problem: Failing to consider the value of foregone alternatives.
Solution: Include opportunity costs in decision-making. They are real costs.
Mistake 4: Ignoring Qualitative Factors
Problem: Focusing only on financial factors and ignoring qualitative factors.
Solution: Consider both quantitative and qualitative factors. Quality, reputation, and employee morale are important.
Mistake 5: Assuming All Variable Costs Are Relevant
Problem: Assuming all variable costs are always relevant.
Solution: Variable costs are only relevant if they differ between alternatives. Some variable costs may be the same under different alternatives.
How Qeeva Advisory Helps You Master Relevant Cost Analysis
We understand that relevant cost analysis can be complex. Many businesses struggle with identifying relevant costs, ignoring sunk costs, and considering opportunity costs. Our professionals specialise in cost analysis, financial modelling, and strategic decision-making.
Our Advisory Services Nigeria help you understand relevant cost analysis and apply it to your business decisions. We help you identify relevant costs, calculate differential costs, and make informed decisions.
Our Financial Advisory services help you build financial models that incorporate relevant costs. We help you evaluate make-or-buy decisions, pricing decisions, and discontinuation decisions.
Our Management Consulting services help you redesign your decision-making processes to incorporate relevant cost analysis.
Our Risk Management services help you identify and manage risks associated with decision-making.
Our Business Plan Service helps you incorporate relevant cost analysis into your business plans.
And because decision-making is about people and processes, our Training & Mentoring Services help you develop the skills of your managers and employees.
Our Service Methodology
We do not do generic. We do thorough, transparent, and actionable.
Step 1: Cost Analysis
We analyse your costs and identify relevant and irrelevant costs. We help you understand which costs matter for your decisions. This step draws on our Advisory Services Nigeria expertise.
Step 2: Decision Analysis
We help you apply relevant cost analysis to your specific decisions. We evaluate make-or-buy decisions, pricing decisions, discontinuation decisions, and special order decisions. Our Financial Advisory team ensures your analysis is robust and actionable.
Step 3: Opportunity Cost Identification
We help you identify and quantify opportunity costs. We ensure that you consider the value of foregone alternatives.
Step 4: Decision Support
We provide data-driven recommendations to support your decisions. We help you choose the alternative with the best financial outcome. Our Management Consulting team ensures your decisions are aligned with your business strategy.
Step 5: Ongoing Monitoring and Support
Decision-making is not a one-time exercise. We help you monitor your decisions, learn from outcomes, and improve your processes. We provide ongoing support through our Advisory Services Nigeria and Risk Management services.
Frequently Asked Questions
Q: What is relevant cost analysis?
A: Relevant cost analysis is a decision-making technique that focuses on costs that differ between alternatives. It helps identify which costs should be considered and which should be ignored.
Q: What are relevant costs?
A: Relevant costs are future costs that differ between alternatives. They are avoidable and change depending on the decision.
Q: What are irrelevant costs?
A: Irrelevant costs are costs that do not differ between alternatives. They are the same regardless of the decision.
Q: Why are sunk costs irrelevant?
A: Sunk costs are costs that have already been incurred and cannot be recovered. They are gone and cannot be changed by any future decision.
Q: What are opportunity costs?
A: Opportunity costs are the benefits foregone by choosing one alternative over another. They are relevant costs that should be included in decision-making.
Q: How do I identify relevant costs?
A: Identify the decision, list all costs, eliminate sunk costs, eliminate costs that do not differ, and identify differential costs.
Q: What is the difference between make-or-buy and relevant cost analysis?
A: Make-or-buy decisions are a common application of relevant cost analysis. Relevant cost analysis is a broader technique for any decision that involves costs.
Q: How can Qeeva Advisory help with relevant cost analysis?
A: We provide cost analysis, decision analysis, opportunity cost identification, decision support, and ongoing monitoring to help businesses make better decisions.
The Bottom Line
Relevant cost analysis is a powerful decision-making tool. It helps you identify which costs matter and which should be ignored. Understanding the difference between relevant and irrelevant costs is essential for make-or-buy decisions, pricing decisions, discontinuation decisions, and special order decisions.
The key is to focus on costs that differ between alternatives. Ignore sunk costs. Include opportunity costs. Consider both quantitative and qualitative factors.
Your job is to be prepared. Understand the concept of relevant costs. Identify the decision. List all costs. Eliminate sunk costs. Eliminate costs that do not differ. Identify differential costs. Choose the best alternative.
With the right approach and the right partner, you can turn relevant cost analysis from a theoretical concept into a practical tool for better decision-making.
The choice is yours.
Suggested Reading from Our Blog
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Current Issues and Trends in Performance Management: A Practical Guide for Modern Businesses – Learn how modern performance management systems leverage real-time data, continuous feedback, and analytics to drive employee engagement and business results.
VAT Computation in Nigeria 2025: Complete Guide to Input Tax, Output Tax, Opening and Closing Inventory Treatment – Learn how relevant cost analysis supports VAT compliance, recovery, and tax planning under Nigeria’s new tax framework.
Related Services
Our Advisory Services Nigeria are staffed by professionals specialising in cost analysis, financial modelling, and strategic decision-making.
Our Financial Advisory services help you build financial models that incorporate relevant costs.
Our Management Consulting services help you redesign your decision-making processes.
Our Risk Management services help you identify and manage risks associated with decision-making.
Our Business Plan Service helps you incorporate relevant cost analysis into your business plans.
Our Training & Mentoring Services help you develop the skills of your managers and employees.
Let’s Talk About Your Decision-Making
Navigating relevant cost analysis can feel complex. At Qeeva Advisory, we understand the challenges businesses face in identifying relevant costs, ignoring sunk costs, and considering opportunity costs.
Whether you need help with make-or-buy decisions, pricing decisions, discontinuation decisions, or special order decisions, we are here to support you.
📞 Call us: (+234) 802 320 0801, (+234) 807 576 5799
📧 Email: info@qeeva.com
📍 Visit us: 5, Ishola Bello Close, Off Iyalla Street, Alausa, Ikeja, Lagos, Nigeria
Contact us today to schedule a consultation. Let us help you make better decisions with relevant cost analysis.
Your journey to better decision-making starts with a conversation. Let’s talk.
Reference Links / Sources
Relevant Cost Analysis – Corporate Finance Institute
Decision Making Techniques – Investopedia
Make-or-Buy Decisions – AccountingTools
