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Fixed and Variable Expenses: How Cost Structure Determines Your Profitability editorial staff editorial staff

Knowing the relationship between revenue and expenses is the key to understanding your business's profitability.

  • A company's cost structure is made up of fixed costs and variable costs.
  • Understanding unit costs is beneficial for understanding the fluctuation of expenses with sales volume.
  • Determine which departments in your company are the most profitable by analyzing the fixed and variable cost structure.

How expenses change concerning changes in revenue determines the cost structure of your business.

The cost structure is stated in terms of fixed and variable expenses. It’s necessary to classify your expenses as either fixed or variable if you want to understand the profitability of your business.

What is cost structure, and why is it important?

For your business to be successful, you must understand the kinds of expenses you'll encounter to keep track of them. The type of expenses your business will have is known as the cost structure, which are the costs your business will incur. There are typically two types of expenses that make up the cost structure: fixed costs and variable costs. Fixed costs are costs that do not change regardless of the output that your business produces; variable costs are costs that change with the volume of production.

Key elements of a cost structure

Fixed and variable costs are the two types of expenses that make up cost structure, so it's important to understand what the elements of these expenses are. For example, variable costs include expenses such as heating, water, and lighting for daily operations and materials required for production; these costs are not fixed, because they change depending on production. Other elements of cost structure may include direct or indirect materials, direct labor, office salary and works in progress. 

Classifying an expense as fixed or variable is determined by how a particular expense fluctuates with sales volume. If an expense increases when sales increase, it's a variable expense. If an expense remains constant when sales increase, it's a fixed expense. Fixed costs plus variable costs equal total costs.

Examples of fixed expenses are rent, overhead, insurance, dues, advertising and administrative salaries. These costs remain the same whether sales increase or decrease. Only when sales increase dramatically, do these costs increase. For purposes of this article, we will assume that fixed costs always remain constant throughout a change in sales.

Variable expenses include raw materials, inventory, production costs, sales commissions and shipping costs. These costs fluctuate in direct relation to sales volume. If sales increase, then variable costs increase. If sales decrease, then variable costs also decrease.

The relationship between sales and expenses

If you want to know how your expenses fluctuate with sales volume, then you must understand unit costs. Because fixed costs don't change as sales volume changes, the fixed cost per unit changes. For example, ABC Chairs has monthly fixed costs of $2,000 to produce chairs. The $2,000 stays the same whether ABC Chairs produces 10 chairs, 100 chairs or 500 chairs.

 Fixed Costs per Unit

This chart illustrates how fixed costs per unit decrease as sales increase.

Because variable expenses change directly as sales volume changes, the variable cost per unit remains the same. For example, if ABC Chairs has variable costs of $500, $5,000 and $25,000 to produce 10 chairs, 100 chairs and 500 chairs, respectively, then the variable cost per unit remains the same.

 Variable Costs per Unit

This chart illustrates how variable costs per unit remain the same as sales increase.

Fixed and variable expenses determine profitability

Measuring expenses as either fixed or variable is commonly used for budgeting and planning purposes. Since net profit is the difference between sales and expenses, knowing how fixed and variable costs behave relative to sales is a must. If you know how costs fluctuate with sales, then you can determine your bottom line at each level of sales volume. 

Profit Chart

Profit analysis chart

On the graph, you can see the relationships working as previously described. As sales increase, so do the variable expenses. Fixed costs remain the same throughout every level of sales volume. Since profit is the difference between sales and total expenses, profit increases as sales increase.

Profit always increases directly relative to sales, as long as variable costs per unit don't exceed sales per unit. If variable costs per unit exceed sales per unit, you have a major cost structure problem. Your business is not viable and will never make a profit.

Another thing to notice is what happens in the graph at a volume of 25 units. At 25 units, profit equals zero. This is called the break-even point. Every business owner should know the sales volume at which the break-even point occurs.

At break-even, sales equal the total of fixed and variable costs. At every sales point above the break-even point, profit increases. At every point below break-even, profit decreases.

Product line, departmental or business-level analysis

You can apply a profitability analysis to your overall business or smaller segments of your business. For instance, it's common to run a profitability analysis using fixed and variable costs on a new product line. This allows you to estimate profits at different sales volumes. You can determine at what sales level that you'll break even.

You can also analyze the fixed and variable cost structure of various departments within your company to determine which departments are the most profitable. You may divest the least-profitable areas of your business and allocate more resources to more profitable areas.

Knowing the fixed and variable cost structure within your business gives you the necessary know-how to determine your annual budget and goals. You'll know how to focus on sales volumes within your company. Sales personnel can be alerted to areas where sales efforts are needed. Underperforming departments can know when it may be necessary to cut fixed costs, such as personnel or overhead.

Knowing the relationship between your sales and expenses is key to running a successful business. The goal of any business is to cover fixed costs and profit from increased sales volume. By understanding the cost structure of fixed and variable costs you can see and maintain your company's profitability. 

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