How Do Fixed and Variable Costs Affect the Marginal Cost of Production?

The total cost of a business is composed of fixed costs and variable costs. Fixed costs and variable costs affect the marginal cost of production only if variable costs exist. The marginal cost of production is calculated by dividing the change in the total cost by a one-unit change in the production output level. The calculation determines the cost of production for one more unit of the good. It is useful in measuring the point at which a business can achieve economies of scale.

Key Takeaways

• Marginal cost of production refers to the additional cost of producing just one more unit.
• Fixed costs do not affect the marginal cost of production since they do not typically vary with additional units.
• Variable costs, however, tend to increase with expanded capacity, adding to marginal cost due to the law of diminishing marginal returns.

Fixed Cost vs. Variable Cost

A fixed cost is a cost that remains constant; it does not change with the output level of goods and services. It is an operating expense of a business, but it is independent of business activity. An example of fixed cost is a rent payment. If a company pays $5,000 in rent per month, it remains the same even if there is no output for the month.

Conversely, a variable cost is dependent on the production output level of goods and services. Unlike a fixed cost, a variable cost is always fluctuating. This cost rises as the production output level rises and decreases as the production output level decreases. For example, say a company owns a manufacturing plant and produces toys. The electricity bill varies as the production output level of toys varies. If no toys are produced, the company spends less on the electricity bill. If the production output of toys increases, the cost of the electricity increases.

Marginal Cost of Production

The marginal cost of production is an economics and managerial accounting concept most often used among manufacturers as a means of isolating an optimum production level. Manufacturers often examine the cost of adding one more unit to their production schedules. At a certain level of production, the benefit of producing one additional unit and generating revenue from that item will bring the overall cost of producing the product line down. The key to optimizing manufacturing costs is to find that point or level as quickly as possible.

Marginal cost of production includes all of the costs that vary with that level of production. For example, if a company needs to build an entirely new factory in order to produce more goods, the cost of building the factory is a marginal cost. The amount of marginal cost varies according to the volume of the goods being produced.

It is not necessarily better or worse for a company to have either fixed costs or variable costs, and most companies have a combination of fixed costs and variable costs. 

A company with greater variable costs compared to fixed costs shows a more consistent per-unit cost and, therefore, a more consistent gross margin, operating margin, and profit margin. A company with greater fixed costs compared to variable costs may achieve higher margins as production increases since revenues increase but the costs will not. However, the margins may also reduce if production decreases.

Other Considerations

Although the marginal cost measures the change in the total cost with respect to a change in the production output level, a change in fixed costs does not affect the marginal cost. For example, if there are only fixed costs associated with producing goods, the marginal cost of production is zero. If the fixed costs were to double, the marginal cost of production is still zero. The change in the total cost is always equal to zero when there are no variable costs. The marginal cost of production measures the change in total cost with respect to a change in production levels, and fixed costs do not change with production levels.

However, the marginal cost of production is affected when there are variable costs associated with production. For example, suppose the fixed costs for a computer manufacturer are $100, and the cost of producing computers is variable. The total cost of production for 20 computers is $1,100. The total cost for producing 21 computers is $1,120. Therefore, the marginal cost of producing computer 21 is $20. The business experiences economies of scale because there is a cost advantage in producing a higher level of output. As opposed to paying $55 per computer for 20 computers, the business can cut costs by paying $53.33 per computer for 21 computers.

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