The Split That Shapes Every Business
Every cost a business pays falls into one of two camps. Either it changes with how much you sell, or it does not. That single distinction, fixed costs versus variable costs, sits underneath almost every useful decision an owner makes: what to charge, how much you need to sell to break even, whether to take on a bigger lease, and how badly a quiet month will hurt.
Most people grasp the idea in a sentence and then trip over the detail. Is rent always fixed? What about a salary that includes commission? Where does your electricity bill go? The honest answer is that the labels are simple but the real world is full of costs that sit on the line between the two.
This guide explains fixed costs vs variable costs in plain English, gives real examples of each, deals with the awkward middle ground of semi-variable costs, and then shows why the split matters far more than most owners realise.
What Is a Fixed Cost?
A fixed cost is a cost that stays the same regardless of how much you produce or sell. Whether you have a record month or sell nothing at all, the bill is the same. It is fixed against your level of output, not fixed forever.
Common fixed costs include:
- Rent and business rates
- Salaries for permanent staff who are paid the same each month
- Directors' remuneration set at a fixed level
- Insurance premiums
- Software subscriptions and accounting fees
- Depreciation on equipment and vehicles
- Loan repayments and interest
The defining feature is that these costs do not flinch when sales move. They are the cost of simply having the business open and ready to trade. That is why fixed costs are sometimes called overheads, and why they are the ones that hurt most in a downturn. The sales can fall to nothing, but the rent still lands on the first of the month.
One point that catches people out: fixed does not mean unchangeable. Your rent can go up at a review, you can hire another permanent member of staff, and your insurance can be renegotiated. The word fixed means the cost does not vary with your sales volume. It can still change for other reasons.
What Is a Variable Cost?
A variable cost is a cost that rises and falls directly with how much you produce or sell. Sell twice as much and your variable costs roughly double. Sell nothing and, in theory, they drop close to zero.
Common variable costs include:
- Raw materials and stock you buy to sell on
- Packaging and delivery for each order
- Payment processing fees charged as a percentage of sales
- Hourly or piece-rate wages tied to production
- Commission paid on sales
- Fuel for deliveries
Variable costs are the direct cost of each sale. They line up closely with what an accountant calls cost of goods sold, the figure you take off revenue to get gross profit. If you sell a wooden table, the timber and the fittings are variable costs. Make ten tables and you buy ten lots of timber. Make none and you buy none.
The useful thing about variable costs is that they scale with you. They feel painful when you are busy, but they only exist because you are making sales, and each sale should be priced to more than cover them. A business in trouble can usually cut variable costs quickly by simply doing less. Fixed costs are far harder to shed in a hurry.
Semi-Variable Costs: The Awkward Middle
Real life is rarely as tidy as two clean columns. Many costs are semi-variable, also called mixed costs, which means they have a fixed part and a variable part.
The classic example is a utility bill. There is often a standing charge you pay no matter what, which is fixed, plus a usage charge that rises the more you consume, which is variable. A mobile phone contract with a monthly allowance plus charges for going over works the same way. So does a salesperson on a basic salary plus commission: the basic is fixed, the commission is variable.
Electricity is the example most owners get wrong. In an office it behaves almost like a fixed cost, because you light and heat the place whether you are busy or not. In a factory that runs more machines when orders rise, a large slice of the electricity bill becomes variable. The same bill can sit in a different camp depending on the business, which is exactly why the labels need judgement rather than a rulebook.
For day-to-day decisions you do not need to agonise over every mixed cost. A sensible habit is to split the obvious ones into their fixed and variable parts and treat small mixed costs as fixed, because the standing element usually dominates. The point is to know which of your costs will follow sales down in a quiet month and which will not.
Is Rent a Fixed Cost?
This question comes up so often it deserves its own answer. In almost all cases, yes, rent is a fixed cost. You agree a figure in a lease and you pay it every month whether the business is flat out or dead quiet. It is the textbook example of a fixed cost because it is completely detached from your sales volume.
There are a couple of exceptions worth knowing. Some retail and hospitality leases include a turnover rent, where part of the rent is calculated as a percentage of sales. That portion behaves like a variable cost. And if you rent equipment or space by the hour only when you need it, that flexes with use and looks variable too. But a standard commercial lease with a fixed monthly figure is fixed, and it is usually one of the largest fixed costs a small business carries. That is why signing a bigger lease is one of the heaviest decisions an owner can make. It raises the floor you have to clear every single month before you make a penny.
Fixed Costs vs Variable Costs at a Glance
| Fixed costs | Variable costs | |
|---|---|---|
| Move with sales? | No | Yes |
| Example | Rent, insurance, salaries | Materials, packaging, commission |
| When sales are zero | Still payable | Fall close to zero |
| Also known as | Overheads | Direct costs |
| Easy to cut quickly? | Hard | Easier |
| Per unit, as you grow | Falls | Stays roughly the same |
That last row is the one most people miss, and it matters. A fixed cost per unit gets smaller the more you sell, because you spread the same rent over more sales. A variable cost per unit stays roughly the same no matter how much you sell. This is the whole reason growth feels good once you pass a certain point: the fixed costs are already paid for, so more sales drop more profit through.
Why the Split Decides Your Break-Even Point
Here is where the two camps earn their keep. The mix of fixed and variable costs sets your break-even point, the level of sales you need just to cover all your costs and make neither a profit nor a loss.
The logic is simple. Every sale brings in revenue and carries its own variable cost. The difference between the two is the contribution, the slice of each sale that is left over to help pay the fixed costs. Once your total contribution has covered all the fixed costs, every further sale starts adding to profit.
The formula is short:
Break-even sales (units) = fixed costs ÷ contribution per unit
Take a business that sells a product for £50, with £20 of variable cost per unit. That leaves £30 of contribution on every sale. If its fixed costs are £30,000 a year, it needs to sell 1,000 units (£30,000 ÷ £30) just to break even. Sell 1,001 and it is in profit. Sell 999 and it is making a loss.
Now change one thing. If the same business signs a bigger lease and pushes fixed costs to £45,000, its break-even jumps to 1,500 units. It has to sell half as much again before it makes anything. Nothing about the product changed. The cost structure did, and the bar moved with it. This is the single most useful thing the fixed and variable split tells you, and it is why we walk through it with owners before they commit to any big jump in overheads.
Our View: The Mix Is a Choice About Risk
In our experience, owners tend to think about costs one bill at a time. The more powerful view is to look at the shape of the whole cost base, because the balance between fixed and variable costs is really a decision about how much risk you are willing to carry.
A business loaded with fixed costs has high operational gearing. When sales are strong it is wonderful, because once you clear that high break-even, the profit rockets, since most of the extra revenue is contribution dropping straight to the bottom line. But when sales fall, those same fixed costs become an anchor. The business keeps paying rent, salaries and finance whether the work comes in or not, and a quiet quarter can turn into a loss very quickly.
A business that keeps costs variable carries less risk. It makes a thinner profit in the good times, because more of every sale goes on direct costs, but it can shrink fast when trade dries up, because the costs fall away with the sales. Outsourcing, using contractors instead of permanent hires, and renting rather than buying are all ways of trading some upside for a lower break-even and a softer landing in a downturn.
Neither shape is right or wrong. A steady, predictable business can afford more fixed costs and enjoy the operational gearing. A young or seasonal business is usually wiser to keep things variable until the income is proven. The mistake we see most often is an owner drifting into a heavy fixed cost base without ever deciding to, signing leases and making permanent hires in a good year, then discovering in a slow one how high the bar has quietly become. Knowing your fixed and variable split, and watching your break-even move when it changes, is how you keep that decision in your own hands. It also protects your working capital, because a high fixed base eats cash steadily whether the sales arrive or not.
How IAK Can Help
We help business owners understand the shape of their costs, not just record them. Clean bookkeeping makes sure every cost is captured and coded so the fixed and variable split is accurate in the first place. Our management reporting turns that into a clear monthly picture, including your break-even point and how much your overheads have crept up, and our accounting and tax planning tie it back to year-end accounts you can rely on.
If you have ever wondered how much you actually need to sell to keep the lights on, that is a break-even question, and it starts with knowing your fixed and variable costs. Contact us for a straight conversation about your numbers.
Sources
- HMRC guidance on business expenses if you are self-employed sets out which running costs can be claimed, many of which are the fixed and variable costs covered here.
- FRS 102, the financial reporting standard most UK small and medium companies apply, governs how costs are recognised and presented in the accounts. Published by the Financial Reporting Council.
- The Companies House filing requirements determine how these costs are summarised in the profit and loss account that companies submit each year.