Variable costs: what they are and how to calculate them

Published Thursday 23 July 2026

Table of contents

• What is a variable cost?
• Examples of variable costs
• Variable costs vs fixed costs
• How to calculate variable costs
• Where variable costs appear in your accounts
• Why variable costs matter
• Semi-variable and stepped costs
• Manage your variable costs with Xero
• FAQs on variable costs

Key takeaways

• A variable cost is a business expense that rises and falls with how much you produce or sell.
• Variable costs are the opposite of fixed costs, which stay the same no matter your level of activity.
• You work out total variable cost by multiplying the number of units by the variable cost per unit.
• Tracking variable costs helps you price your products, plan your budget and understand your break-even point.

What is a variable cost?

A variable cost is an expense that changes in line with your business activity: it goes up when you make or sell more, and down when you make or sell less.

Variable costs are the opposite of fixed costs, which stay the same whether business is busy or quiet. If you run a bakery, the flour and sugar you buy are variable costs, because you use more of them when you bake more. When output drops, so does the amount you spend.

Examples of variable costs

Variable costs show up across many parts of a business, and they tend to grow as your sales grow. Here are common examples you might recognise in your own accounts:

• Inventory and raw materials you buy to make your products
• Packaging and shipping that scale with the number of orders
• Transaction fees for card, digital wallet and direct debit payments
• Contractors you hire in during busy periods
• Marketing spend that rises when you push for more sales
• Travel costs for your sales team
• Commissions and referral bonuses paid on each sale

Variable costs vs fixed costs

To manage your money well, it helps to know which of your costs move with activity and which stay put. Every cost your business has is either variable or fixed.

Variable costs change with how much you produce or sell, so they rise in busy months and fall in quiet ones. Fixed costs stay the same regardless of your output, which makes them easier to predict. Examples of fixed costs include rent, insurance and the salaries of permanent staff.

How to calculate variable costs

Working out your variable costs is straightforward once you know your output and your cost per unit. There are two simple formulas you'll use most often.

Total variable cost = total output x variable cost per unit. To find the cost per unit on its own, use: variable cost per unit = total variable costs / units produced.

Here's a worked example. Say you run a bakery and each cake costs £3 in ingredients plus £2 in packaging, giving a variable cost of £5 per cake. If you bake 100 cakes, your total variable cost is 100 x £5, which comes to £500.

Where variable costs appear in your accounts

Once you've worked out your variable costs, it helps to know where they sit in your books. Most of them appear on your profit and loss account.

Variable costs usually fall under cost of sales, sometimes called cost of goods sold. These are the direct costs of making the products or services you sell, so they change with your sales volume rather than staying flat month to month.

Why variable costs matter

Keeping an eye on your variable costs gives you a clearer picture of your profit on every sale. They feed into some of the most important decisions you'll make.

Because variable costs shape the true cost of each product, they guide how you set your prices. They also affect your break-even point, the moment your sales cover your costs. Understanding them helps you build a realistic small business budget and keep on top of your cash flow.

Variable costs can change from week to week and month to month, which makes them harder to budget than fixed costs. Costs like fuel or energy can move quickly, so it's worth reviewing them often.

Semi-variable and stepped costs

Not every cost is cleanly variable or fixed. Some sit in between, and knowing about them helps you plan more accurately.

Semi-variable costs, also called mixed costs, have a fixed portion plus a part that changes with activity. A mobile phone plan with a set monthly fee plus charges for extra usage is a good example.

Stepped costs stay flat up to a point, then jump when you cross a threshold. If hiring one more employee lets you make another 200 products, your wage costs rise in a single step rather than climbing smoothly with each unit.

Manage your variable costs with Xero

Tracking your variable costs by hand takes time you'd rather spend running your business. Xero accounting software brings your income and expenses together in one place, so you can see how your costs move as your sales change.

With clear reports and real-time figures, you can spot rising costs early, price your products with confidence and plan ahead. Try Xero and get one month free.

FAQs on variable costs

Here are answers to some frequently asked questions about variable costs.

What is the formula for total variable cost?

Total variable cost equals your total output multiplied by the variable cost per unit. So if you make 200 items at £4 each, your total variable cost is £800.

How do you calculate variable cost per unit?

Divide your total variable costs by the number of units you produced. This tells you how much each single unit adds to your costs.

Is marginal cost the same as variable cost?

They're closely related but not identical. Marginal cost is the cost of making one more unit, while variable cost covers the changing costs across all the units you produce.

How do variable costs affect the break-even point?

Higher variable costs leave less from each sale to cover your fixed costs, which pushes your break-even point up. Lowering them means you reach break-even with fewer sales.