Fixed costs do not change when output changes in the short run. Variable costs rise as output rises. Total cost is the two added together: total cost = fixed cost + variable cost. This sorting appears in almost every firm question in firms, costs and scale.
What is the difference, step by step?
Ask one question about each expense: if the firm made 500 more units next month, would this bill go up?
- If the bill stays the same, it is fixed. Examples: rent, insurance, loan repayment on equipment, a manager’s monthly salary.
- If the bill goes up with output, it is variable. Examples: raw materials, packaging, hourly wages paid per unit made, delivery fuel.
- Total cost combines both at the output level in the question.
Some items are mixed, such as an electricity bill with a standing charge plus usage. Split them if the case gives the split. If it does not, say which part you are treating as which, and why.
Worked example
Mawar Bakery (a fictional shop) has these monthly figures:
- Shop rent: RM2,000
- Oven loan repayment: RM600
- Insurance: RM400
- Flour and ingredients: RM1.20 per loaf
- Packaging: RM0.30 per loaf
Find the total cost of making 2,000 loaves and 4,000 loaves.
Step 1, sort the costs. Rent, loan and insurance are fixed. Flour and packaging are variable.
Step 2, total fixed cost. RM2,000 + RM600 + RM400 = RM3,000, at every output level.
Step 3, variable cost per loaf. RM1.20 + RM0.30 = RM1.50.
Step 4, calculate each output.
| Loaves | Fixed cost (RM) | Variable cost (RM) | Total cost (RM) |
|---|---|---|---|
| 2,000 | 3,000 | 2,000 × 1.50 = 3,000 | 6,000 |
| 4,000 | 3,000 | 4,000 × 1.50 = 6,000 | 9,000 |
Fixed cost stayed at RM3,000 while variable cost doubled, so total cost rose by RM3,000, not doubled.
The mistake to watch for
Mistaken answer: “Total cost at 4,000 loaves is RM12,000, because 4,000 is double 2,000 and so total cost doubles.”
This treats every cost as variable. Doubling output doubles only the variable part (RM3,000 to RM6,000). The fixed RM3,000 stays put, giving RM9,000.
Another version of the slip is calling rent variable because “it is paid every month”. Regular payment is not the test. Change with output is.
Check yourself
1. A fictional print shop pays RM1,500 monthly rent, RM800 for paper per 1,000 sheets and RM300 for machine insurance. Name the fixed and variable costs.
Show answer
Fixed: rent (RM1,500) and insurance (RM300). Variable: paper, because the cost depends on the sheets printed.
2. A firm has fixed costs of RM5,000 and variable costs of RM4 per unit. Find total cost at 1,500 units.
Show answer
Variable cost = 1,500 × 4 = RM6,000. Total cost = 5,000 + 6,000 = RM11,000.
3. At 1,000 units a firm’s total cost is RM9,500 and variable cost is RM6,000. What are its fixed costs?
Show answer
Fixed cost = total cost − variable cost = 9,500 − 6,000 = RM3,500.
Where this leads next
With costs sorted, the next skill is to calculate average and marginal-style changes. You can test the whole module in the mixed practice set.
Sorting costs well is mostly pattern practice with cases that mix things up. In online one-to-one Economics tuition, a teacher can build those cases around the errors you actually make.