What Is Marginal Cost and How to Calculate It

If you run a production- or service-based business, you need to know how much it’s costing you to produce or offer one more unit or service so that you can manage your pricing.

This is where the economic term marginal cost (MC) plays a big role. Simply defined as the extra total cost of producing one additional unit in your production line, its implications go beyond pricing. It also affects your production quantities and business decision-making processes.

Many UK businesses use marginal cost analysis to optimise production efficiency, control expenses, and improve profit margins.

In this article, we do an in-depth analysis of what marginal cost is, provide the formula for how to calculate marginal cost and more. 

What Is Marginal Cost?

Marginal cost is the additional cost incurred by a business from producing one more unit of a good or service. This is important because it can help you determine the optimal production level and pricing strategy based on quantifiable data.

In economics, the term “marginal” is often used to indicate change. So, when we talk about MC, we’re talking about a change in total cost (TC) to produce an additional unit.

In practice, it works like this: as you want to produce more, you need more inputs. This is where we make some key assumptions. For example, in the production process, some things stay consistent (e.g. technology, the number of labourers, machines, etc.).

And initially, when you start producing, the more you produce that item, the change in your TC has a tendency to come down.

But this is only for a brief period of time. As you then continue to produce, you’re putting additional pressure on the factors of production. These include labour, machines, technology – in other words, what’s available at your business at that point in time.

However, the costs of production tend to start to increase afterwards.

And because MC means a change in the TC, then your marginal cost starts to increase. A change in the total cost means a change in the marginal cost. The most efficient place to produce anything would be at the lowest end of the marginal cost curve. 

Additionally, marginal cost can’t be looked at in isolation from marginal revenue (MR), which is the connected term used to describe the income from selling that extra unit. We cover this in more detail below.

There are many reasons why understanding marginal cost is important. However, the key advantages you should be aware of when doing this calculation are that it supports resource allocation and cost management decisions.

Why Marginal Cost Matters for Businesses

Calculating marginal cost is important for businesses. For instance, a manufacturer in the UK or a service provider can use this calculation to evaluate the financial impact of increasing their output. 

But that’s not all. Knowing your marginal cost also:

• Helps identify the most cost-efficient production scale;
• Informs pricing strategies and profit-maximisation decisions;
• Detects inefficiencies and opportunities for cost reduction;
• Guides business owners on whether to expand, pause or scale production.

All this is aimed to help you understand and work toward profit maximisation as you determine what your optimal production level is.

The Marginal Cost Formula

To calculate marginal cost, use the following formula:

• Marginal Cost (MC) = Change in Total Cost (TC) / Change in Quantity

Or:

• Marginal Cost (MC) = (Total Cost₂ – Total Cost₁) / (Quantity₂ – Quantity₁)  

Now, let’s break this down a bit further. Since total cost or TC includes both fixed and variable costs, you’ll need to work out what your total cost is. 

The formula for calculating TC is:

• TC = TFC (Total Fixed (Constant) Cost) + TVC (Total Variable Cost)

Note that Total Fixed Cost is also referred to as Total Constant Cost. As for calculating quantity, remember that it represents total output or units produced. Also, bear in mind that only variable costs change directly with production, while fixed costs remain constant.

Example of Calculating Marginal Cost

Here’s an example put into practice: 

Say that you want to make ice cream for sale.

Your fixed costs could be the cost of your freezer and your variable costs would be the inputs in making the ice cream, such as cream.

In the short run, the fridge does not change size (fixed cost remains constant) but the more ice cream you produce, the more cream you will require (variable costs fluctuate and increase).

In the long run, you could purchase a second freezer. But in this calculation, we assume you’ll only be working with only one freezer. Thereafter, the freezer remains a fixed cost going forward.

Note: We’re only speaking of the variable and fixed costs in the short run, which means the fixed costs cannot change and that means you’re only dealing with one freezer.

And as you produce more, the more ice cream you’ll want to make, the more cream (variable cost) you’ll need to purchase. But the total production is limited by the size of the freezer. Given this, as you produce more ice cream, the variable cost increases but the fixed cost remains the same.

Step-by-Step: How to Calculate Marginal Cost

Below is a step-by-step guide on how to calculate MC with a fictional example:

• Step 1: Identify TC before and after production change: Gather total cost data for two production levels such as 100 units (initial) and 120 units (new).
• Step 2: Determine the change in total cost: Subtract the initial total cost from the new total cost.
• Step 3: Determine the change in quantity: Subtract the initial number of units from the new quantity produced.
• Step 4: Apply the formula:
  • Total cost at 100 units = £2,000
  • Total Cost at 120 units = £2,300
  • Change in Cost = £300
  • Change in Quantity = 20
  • Marginal Cost = £300 ÷ 20 = £15 per unit

In short, the £15 represents the additional unit cost to produce each further unit beyond 100.

Components of Marginal Cost

Based on the example of producing ice cream mentioned earlier, it’s clear that to do a marginal cost analysis, you need to be aware of your fixed and variable costs so that you can factor them into your calculation. Here’s what each one means:

Fixed costs

Fixed costs are sometimes referred to as “constant” costs because these costs stay constant throughout the production process in the short run. 

In other words, these are the costs that remain unchanged regardless of the production levels (e.g., rent, salaries, insurance).

Variable costs

Variable costs, on the other hand are costs that vary with output (e.g., materials, labour, packaging, utilities). 

For instance, a variable cost would be considered the cost of raw materials increasing as production expands.

Marginal Cost Curve Explained

Marginal cost can be plotted on a graph with an x and y axis. It is depicted by the marginal cost curve, which forms a “hook” or a U-form shape.

In practice, what we see is that at first, your production costs fall due to economies of scale and production efficiency. But eventually, your costs will start to rise because of the law of diminishing returns due to capacity constraints. (Think back to the single freezer in the ice-cream making example above).

The marginal cost curve analysis is related to optimal production levels and profit maximisation. As such, the most efficient costs of production is where the marginal cost is at its lowest. 

Marginal Cost vs. Average Cost

Marginal cost and average cost (AC) are different sides to the same coin. 

To help you understand the difference easier, we’ve created a short comparison table below:

	Marginal Cost	Average Cost
Definition	Cost of producing one extra unit	Total cost divided by total units
Purpose	Determines cost efficiency of scaling	Shows overall production cost efficiency
Impact	Affects short-term pricing	Used in long-term planning and benchmarking
Formula	Marginal Cost = Change in Total Cost / Change in Quantity	Average Cost = Total Cost / Quantity

Being able to access marginal cost and average cost data for your business is an incredibly useful way to help you create a more profitable cost structure that drives your market prices.

Marginal Cost and Marginal Revenue Relationship

Marginal revenue (MR) is the additional revenue earned from selling one more unit. It is equal to the change in the total revenue divided by change in total quantity.

• MR = Change in Total Revenue/Change in Total Quantity

Marginal revenue can also be plotted on a graph with the x-axis representing your quantity or what’s being produced, while the y-axis represents your costs. The assumption is that everything that’s being produced is sold without any stock pileups. The importance of calculating MR is vital. That’s because profit is maximised when MR = MC.

For instance, if your MR > MC, you should increase your production.

Conversely, if your MR < MC, you need to reduce production.

Let’s discuss this curve in a bit more detail. In the early part of your production, your MCs tend to decrease while the MR tends to start increasing. In other words, the more you’re producing the greater your MR and the lower your MCs.

However, due to the law of diminishing returns, the MC starts to increase but the MC increases more than MR. This means that your MC is higher than your MR leading toward higher inefficiency.

The point where the MC intersects MR is the point where you’ll make the maximum profit. In other words, when choosing the most efficient quantity to produce, the producer would usually make his decision to limit his production to a certain quantity where the MC = MR and this can be seen on the x-axis of the graph.

Note: This still refers to production and processes during the short-term period.

Marginal Cost Analysis in Business Strategy

Doing a marginal cost analysis should be an important part of your business strategy. Why? 

There are many reasons this calculation can help you, which include:

• It helps you find your optimal quantity produced and to determine where you would make the maximum profit.
  
• It is useful for analysing the financial impact of scaling production or launching new product lines.
  
• It enables data-driven decision-making in cost control and pricing.

For instance, a UK bakery can assess whether producing 500 extra loaves of bread improves or reduces profit margins.

Factors Affecting Marginal Cost

Marginal cost can seem like a fixed cost. However, it’s always fluctuating and this is not only due to internal changes at your business but is also due to external factors. 

Here are some aspects that come into play that you should be aware of when performing this calculation:

• Changes in material prices or labour costs;
  
• Production technology improvements e.g. by improving skills to improve efficiency of workers;
  
• Resource availability or supply chain conditions;
  
• Economies and diseconomies of scale (i.e., increase in your output by the same number of inputs means an increase in economies of scale, whereas a decrease in output by the same number of inputs results in decreasing economies of scale);
  
• Government regulations and UK market conditions (e.g., energy costs, wage changes).

In short, your production volume needs to be optimised. But to optimise it, you need to be aware of both internal and external factors (e.g. fixed and variable costs) which impact the incremental cost of doing business.

Real-World Examples of Marginal Cost Application

If you’re wondering if the marginal cost calculation applies to you, you’re at the right place. Such calculations have real-world implications across multiple industries, helping business owners in different niches thrive. 

Some examples of these industries include:

• Manufacturing: determining when to increase production lines or outsource (tariff adjustments affect the cost of inputs);
  
• SaaS businesses: calculating the cost of serving additional subscribers;
  
• Retail: deciding whether to extend opening hours or add staff;
  
• Hospitality: evaluating whether extra seasonal bookings justify additional operational costs.

This is just a short list but it illustrates that marginal cost analysis can significantly help you make better and more effective production decisions.

Challenges in Marginal Cost Calculation

Calculating marginal cost is not without its challenges. For effective cost management and efficient production capacity, you need to measure cost changes across important categories. 

Some businesses may struggle more than others, largely owing to:

• Difficulty separating fixed and variable costs accurately because fixed costs can change e.g. increases in rent;
  
• External factors like inflation and currency fluctuations;
  
• Complex cost structures in service-based industries;
  
• Need for reliable financial data and regular updates.

Bearing these challenges in mind, and preparing yourself with accurate data, can help you improve your costs of production as you work on calculating your marginal cost at key time points of your business’ growth.

Conclusion  

In summary, marginal cost (MC) is the additional expense incurred by producing one more unit of a good or service. By applying the formula, you can pinpoint the exact moment where production shifts from profitable to inefficient.

This calculation is a cornerstone of strategic planning, as it empowers you to set accurate prices, optimise your resource allocation and identify your "sweet spot" for profit maximisation.

While external factors like inflation can complicate your data, consistent monitoring ensures you maintain a competitive advantage in a shifting market.

To better manage these fluctuating costs and streamline your incoming revenue, consider how a dedicated business account can simplify your financial tracking.

Ultimately, mastering your marginal cost allows you to scale with confidence and precision.

Frequently Asked Questions

What is the marginal cost in simple terms?

In simple terms, marginal cost is the "extra" expense your business pays to produce exactly one more unit of a product or service. It helps you decide if increasing production is financially worth it by revealing whether the cost of that next item is falling or rising due to efficiency and resource limits.

What is the formula for the marginal cost?

The marginal cost is calculated by dividing the change in total costs by the change in the total quantity produced. This formula allows you to see the specific impact of scaling production on your budget.

What is the difference between total cost and marginal cost?

Total cost is the sum of every expense (fixed and variable) required to produce your entire current output. Marginal cost, however, focuses only on the incremental change. While total cost tells you how much you’ve spent overall, marginal cost tells you how much the next step in production will actually cost.

How to calculate marginal profit?

Marginal profit is the movement in total profit when one additional unit is produced and sold. You calculate it by subtracting the marginal cost from the marginal revenue (MR - MC). If your marginal revenue is higher than the marginal cost per unit, your business is increasing its overall profitability with that extra sale.

What are operating costs?

Operating costs are the ongoing expenses required to keep your business running day-to-day. This includes "Opex" items like rent, utilities, inventory, payroll, and insurance. Unlike one-time capital investments (like buying a building), operating costs are continuous and directly related to your business’s ability to function and generate revenue.

What are the four types of expenses?

In business accounting, expenses are generally categorised into four types: Fixed Expenses (rent), Variable Expenses (raw materials), Accrued Expenses (unpaid debts or obligations) and Operating Expenses (daily administrative costs).