Which Costs Are Fixed and Which Are Variable?
One question sorts almost every cost, and getting it wrong is why most break-even numbers are too optimistic. Here is how to classify costs and use them properly.
Updated on 10 min read
Quick answer: one question sorts almost every cost
Ask this about each cost: if I sold one more unit this month, would this cost go up?
- Yes, it goes up. Variable cost. It belongs in your variable cost per unit.
- No, it stays the same. Fixed cost. It belongs in your monthly fixed cost total.
- Partly. Semi-variable. Split it, then put each part in the right place.
Note the wording: does the cost change in total. Fixed costs per unit fall as you sell more, which trips people up, but the total does not move.
Why misclassifying costs ruins the answer
Break-even is fixed costs divided by contribution margin per unit. Both parts of that fraction depend on classification, so a misplaced cost does not shift the answer slightly. It moves the numerator and the denominator at once.
Put a variable cost into fixed costs and you overstate contribution margin, making every sale look more profitable than it is. Put a fixed cost into variable cost per unit and you do the reverse, making a viable product look hopeless. Either way the pricing decision that follows is built on a number that was never right.
This is also why lumping everything into one pile called "expenses" makes break-even impossible to calculate at all.
Key terms in plain English
These come up whenever costs are split for planning or pricing.
- Fixed cost
- A cost that stays the same in total whether you sell one unit or a thousand. Rent is the clearest example: the landlord charges the same amount on a quiet month.
- Variable cost
- A cost that rises and falls in total with the number of units sold. Materials are the clearest example: no sales means no materials used.
- Semi-variable cost
- Also called a mixed cost. It has a fixed base plus a usage component, such as an electricity bill with a standing charge plus consumption.
- Contribution margin
- Selling price per unit minus variable cost per unit. It is the amount each sale contributes towards covering fixed costs, and profit once they are covered.
- Break-even point
- The sales level where total revenue exactly equals total costs. Profit at this point is zero, which is not the same as the business being comfortable.
- Relevant range
- The activity range over which a fixed cost genuinely stays fixed. Outside it, fixed costs step up, such as when you need a second unit of premises.
- Direct cost
- A cost traceable to a specific product or job. Direct and indirect describe traceability, not behaviour, so a direct cost is not automatically variable.
- Margin of safety
- How far current or forecast sales sit above the break-even point. It shows how much sales could fall before the business starts making a loss.
Sorting common business costs
Use this as a starting point rather than a rule. The same cost can behave differently in different businesses, so always apply the one-more-unit test to your own situation.
| Cost | Usually | Reason |
|---|---|---|
| Shop or office rent | Fixed | Same amount whether you sell nothing or everything |
| Raw materials | Variable | One more unit made means more material used |
| Packaging | Variable | Each unit sold needs its own packaging |
| Sales commission | Variable | Paid as a share of each sale |
| Payment gateway fees | Variable | Charged per transaction |
| Salaried admin staff | Fixed | Paid the same regardless of volume |
| Hourly staff scaling with orders | Variable | Hours rise and fall with demand |
| Insurance premium | Fixed | Set annually, unrelated to volume |
| Electricity | Semi-variable | Standing charge plus usage |
| Mobile or internet plan | Semi-variable | Base plan plus overage |
| Depreciation of equipment | Fixed | Charged by time, not by units produced |
Depreciation is worth a second look. It is fixed here because it is charged by time, and the depreciation calculator will give you the annual amount to divide across your months.
Splitting a semi-variable cost
Mixed costs are the ones people give up on. The simplest reliable method uses your highest and lowest activity months, which is why it is called the high-low method.
Say your electricity bill looked like this:
| Month | Units produced | Electricity bill (RM) |
|---|---|---|
| Quietest month | 200 | 350 |
| Busiest month | 500 | 650 |
Step 1. Find the variable rate per unit. Divide the change in cost by the change in units: (650 - 350) / (500 - 200) = 300 / 300 = RM 1.00 per unit.
Step 2. Find the fixed base. Take either month and remove the variable part: 350 - (200 x RM 1.00) = RM 150.
Step 3. Check it against the other month. 650 - (500 x RM 1.00) = RM 150. The two agree, so the split is consistent.
The RM 150 goes into fixed costs and the RM 1.00 goes into variable cost per unit. Repeat for every mixed bill you have.
Four traps that skew the result
These four account for most wrong break-even figures. The first is by far the most common.
1. Leaving your own salary out of fixed costs
The most common reason a break-even number looks reassuring and is not.
Example
A business with RM 5,150 of other fixed costs and RM 26 contribution per unit breaks even at 199 units. Add the owner's RM 4,000 salary and the real figure is 352 units.
Why it matters. That is roughly 43 percent more sales needed than the original number suggested. If you work in the business, your time has a cost, and leaving it out means the break-even point only covers everyone except you.
What to do. Include a realistic market salary for your own role in fixed costs, even if you currently take drawings instead of a wage.
2. Treating semi-variable costs as entirely fixed
Lumping a mixed bill into fixed costs understates how fast costs grow.
Example
Treating a whole electricity bill as fixed hides the fact that part of it rises with every unit produced.
Why it matters. The usage portion belongs in variable cost per unit. Leaving it in fixed costs overstates contribution margin, which makes each sale look more profitable than it is and pushes the break-even estimate too low.
What to do. Split mixed costs into their fixed base and usage rate using the method in the next section.
3. Putting depreciation or overhead into variable cost per unit
This is the opposite error and makes the business look worse than it is.
Example
Adding a share of monthly depreciation and rent to each unit inflates variable cost per unit and shrinks contribution margin.
Why it matters. Depreciation is charged by time, not by units sold, so it is a fixed cost. Allocating overheads per unit mixes an arbitrary spread into a figure that should only contain costs genuinely caused by one more sale.
What to do. Ask whether the cost would disappear if you sold one fewer unit. If it would not, it is fixed.
4. Assuming direct costs are always variable
Direct versus indirect is a different question from fixed versus variable.
Example
A supervisor employed full-time on one product line is a direct cost of that line, but the salary does not change with units produced, so it is fixed.
Why it matters. Direct and indirect describe whether a cost can be traced to a product. Fixed and variable describe how a cost behaves with volume. A cost can be direct and fixed, or indirect and variable.
What to do. Classify for break-even purposes on behaviour only. Ignore traceability when filling in the calculator.
Worked example: turning sorted costs into a break-even point
A small product business sells at RM 50 per unit. After classifying everything and splitting the electricity bill, the monthly picture looks like this.
| Fixed costs per month | RM |
|---|---|
| Rent | 3,000 |
| Owner salary | 4,000 |
| Admin staff | 1,800 |
| Insurance | 200 |
| Electricity, fixed base | 150 |
| Total fixed costs | 9,150 |
| Variable cost per unit | RM |
|---|---|
| Materials | 18 |
| Packaging | 2 |
| Sales commission | 3 |
| Electricity, usage rate | 1 |
| Total variable cost per unit | 24 |
Contribution margin per unit = RM 50 - RM 24 = RM 26. Each sale puts RM 26 towards fixed costs.
Break-even units = RM 9,150 / RM 26 = 351.9, so 352 whole units.
Break-even sales = 352 x RM 50 = RM 17,600 of revenue per month.
Now the contrast that matters. Leave the owner salary out and fixed costs drop to RM 5,150, giving a break-even of 199 units. That is 43 percent fewer sales than the business actually needs, and it is the version most people calculate first.
Enter the three figures into the break-even calculator to get contribution margin, break-even units, and break-even sales without doing the arithmetic yourself. Remember that break-even means zero profit, so treat it as the floor rather than the target.
Classification checklist
- I asked of every cost whether it changes when I sell one more unit.
- I included a realistic salary for my own role in fixed costs.
- I split semi-variable bills into a fixed base and a usage rate.
- I kept depreciation and rent out of variable cost per unit.
- I classified on behaviour rather than on whether a cost is traceable.
- I checked my fixed costs are still valid at the sales level I am planning for.
- I used a consistent period for fixed costs and the sales target.
- I recalculated after any change in rent, wages, or supplier pricing.
This guide explains general costing concepts for learning and planning. It is not accounting or financial advice for a specific business.
Costs sorted? Work out your break-even
Enter fixed costs, selling price, and variable cost per unit to see contribution margin, break-even units, and break-even sales.
Sources
This guide is based on the official pages below, last checked on 19 August 2026. Where they disagree with anything written here, they are the authority.
- IAS 2 Inventories
Where cost behaviour meets financial reporting: production overhead in the cost of conversion. MASB adopts this in Malaysia as MFRS 102. Classifying costs as fixed or variable is management accounting and is not itself set by a reporting standard.
How this content is put together is set out in our editorial policy.
Fixed and Variable Cost FAQs
Is a salary a fixed or variable cost?
It depends on how the person is paid. A salaried employee who receives the same amount regardless of sales is a fixed cost. Hourly staff whose hours rise and fall with demand, or staff paid by commission or piece rate, are variable. Many businesses have both, and the two should be separated rather than averaged.
Are fixed costs the same as indirect costs?
No. Fixed and variable describe how a cost behaves when volume changes. Direct and indirect describe whether a cost can be traced to a specific product or job. A supervisor dedicated to one product line is direct and fixed, while a shared delivery charge can be indirect and variable.
What is the difference between contribution margin and gross profit?
Contribution margin subtracts only variable costs from revenue, so it isolates what each extra sale contributes towards fixed costs. Gross profit subtracts cost of goods sold, which usually includes some fixed production costs. They are calculated differently and are not interchangeable.
Do fixed costs stay fixed forever?
Only within a relevant range. Fixed costs step up once you outgrow current capacity, such as renting a second unit or hiring another supervisor. A break-even figure is only valid for the range of activity your current fixed costs actually support.
What is the margin of safety?
The margin of safety is the gap between your expected sales and your break-even point. If break-even is 352 units and you expect to sell 500, the margin of safety is 148 units, or about 30 percent. It shows how far sales could fall before the business makes a loss.
Does the break-even calculator handle semi-variable costs?
Not directly, because it takes a single fixed cost total and a single variable cost per unit. Split any mixed cost yourself first, then add the fixed base to your fixed cost total and the usage rate to your variable cost per unit. The calculator then works correctly.