Unveiling the Phantom: The Irrelevance of Sunk Costs in Finance

October 19, 2023

When it comes to financial decision making, understanding the relevance of costs is critical. Costs play a significant role in determining the profitability and sustainability of a business. However, not all costs are equally relevant in all situations. Some costs are essential to decision making, while others may be irrelevant and should not be considered. In this article, we will explore the concept of cost relevance and identify the type of cost that is always irrelevant in financial analysis.

Sunk Costs

Sunk costs are expenses that have already been incurred and cannot be recovered. These costs are irrelevant because they do not affect future decisions. No matter what decision is made, sunk costs remain the same. For example, consider a company that has invested a significant amount of money in developing a prototype for a new product. If management decides not to produce the product because of market changes, the money invested in the prototype becomes a sunk cost. The decision should be based on future profitability and market conditions rather than trying to recover the sunk cost.
By ignoring sunk costs, decision makers can focus on the future costs and benefits associated with the available alternatives. This approach allows for a more objective evaluation of potential outcomes and helps to make rational decisions that maximize profitability and overall business success.

Opportunity Cost

Opportunity cost refers to the benefits or profits foregone by choosing one alternative over another. It represents the value of the next best alternative that is sacrificed in the decision-making process. While opportunity costs are highly relevant in financial analysis, they are not always considered in traditional accounting practices.

For example, let’s say a company has a piece of land that it can either use for its own expansion or lease to another company. If the company decides to use the land for its own expansion, the opportunity cost would be the potential rental income it could have earned by leasing it out. By not considering the opportunity cost, the company may make a decision that appears financially beneficial in the short term, but could result in lost opportunities for additional income in the long term.

Fixed Costs

Fixed costs are expenses that do not vary with changes in production levels or sales volumes. Examples of fixed costs include rent, insurance premiums, and salaries. While fixed costs are relevant to short-term decision making, they become irrelevant in the long run. This is because fixed costs are unavoidable no matter what decision is made.

Consider a manufacturing company that is evaluating whether to produce and sell a new line of products. The fixed costs, such as rent and insurance, would remain the same regardless of whether the company decides to proceed with the new product line or not. Therefore, these fixed costs should not be the sole basis for the decision. Instead, the focus should be on variable costs, such as material and labor costs, which are directly related to production volume and sales.

Social costs

Social costs are the costs to society as a whole of certain business activities or decisions. These costs include environmental pollution, public health problems, or the depletion of natural resources. Although social costs have a significant impact on society, they are often not fully considered in traditional financial analysis.
For example, a manufacturing plant that emits pollutants into the air can cause health risks and environmental damage to the surrounding community. While the costs associated with mitigating these negative impacts can be significant, they are often not considered in the decision-making process from a financial perspective. However, from a broader societal perspective, these costs are highly relevant and should be taken into account when assessing the overall impact and sustainability of a business.


Cost analysis is an important aspect of financial decision making. While many costs are relevant and should be carefully evaluated, there are certain types of costs that are never relevant. Sunk costs, opportunity costs, fixed costs, and social costs fall into this category. By understanding the irrelevance of these costs, decision makers can make more informed and rational decisions that maximize profitability and contribute to the long-term success and sustainability of their organizations.
It is important to note that while these costs may be irrelevant in some contexts, they may have value in other areas, such as legal or ethical considerations. Therefore, a comprehensive analysis that considers multiple perspectives is essential to making informed decisions that are consistent with an organization’s overall goals and values.


Which type of cost is always irrelevant?

The type of cost that is always irrelevant is a sunk cost.

What is a sunk cost?

A sunk cost is a cost that has already been incurred and cannot be recovered. It is a cost that has been paid or committed to and is not affected by any future actions or decisions.

Why is a sunk cost considered irrelevant?

A sunk cost is considered irrelevant because it has already been spent and cannot be changed. When making decisions, only the future costs and benefits should be taken into account, not the sunk costs.

Can you provide an example of a sunk cost?

One example of a sunk cost is purchasing a non-refundable concert ticket. Once the ticket is bought, the cost is sunk, regardless of whether or not the person attends the concert.

What is the concept of “sunk cost fallacy”?

The sunk cost fallacy is a cognitive bias where individuals continue to pursue an option or course of action because of the investments they have already made, even when the current or future benefits do not justify the additional costs.

How can one avoid falling into the sunk cost fallacy trap?

To avoid falling into the sunk cost fallacy trap, it is important to focus on the future costs and benefits and make decisions based on the expected outcomes rather than past investments. Evaluating options objectively and considering the potential gains and losses can help mitigate the influence of sunk costs.