Every cost your business incurs behaves in one of two ways as sales rise and fall. Fixed costs hold steady whether you sell one unit or a thousand, while variable costs climb with each additional sale. Understanding which is which is the foundation of pricing, break-even analysis, and cash planning. The balance between the two, known as your cost structure, also determines how risky and how scalable your business is.
What counts as fixed
Fixed costs are the commitments you owe regardless of how busy you are in a given month. Rent, insurance premiums, salaried staff, loan payments, and most software subscriptions fall here. They are predictable, which helps planning, but they do not shrink when sales drop, which is what makes a slow month painful. Fixed costs are only fixed within a range; hiring a second location resets them to a higher level.
What counts as variable
Variable costs are incurred only when you make a sale, so they scale directly with volume. Raw materials, packaging, shipping, sales commissions, and card processing fees are classic examples. Because they rise with revenue, they rarely threaten survival on their own, but they compress the profit on every unit. The variable cost per unit is the number you subtract from price to find contribution margin.
Mixed and stepped costs
Many real costs are not purely one or the other. A phone plan with a base fee plus per-minute charges is mixed, and you split it into fixed and variable parts for planning. Some costs are stepped: a single manager can handle output up to a point, then you must hire another, jumping the fixed cost in a step. Recognizing these shapes keeps your projections from breaking at exactly the moment you grow.
Operating leverage and risk
A business heavy in fixed costs has high operating leverage, meaning profits swing sharply as sales move. Once fixed costs are covered, extra sales are highly profitable, but a downturn is dangerous because the costs do not fall with revenue. A variable-heavy business earns thinner margins per unit but bends more easily in a slump. Choosing your mix is really choosing how much risk and scale upside you want.
A print shop pays 4,000 dollars a month in rent and salaries no matter what. Ink and paper cost 3 dollars per poster, and each poster sells for 15 dollars. The rent is fixed, the ink and paper are variable, and the 12 dollar gap is what covers the fixed costs and profit.
Key takeaways
- Fixed costs stay constant with volume; variable costs rise with each sale.
- Variable cost per unit is what you subtract from price to get contribution margin.
- Mixed costs have both a fixed base and a usage-based part.
- High fixed costs mean more scale upside but more downside risk in a slump.
Common mistakes
- Assuming fixed costs are permanent when they actually step up as you grow.
- Ignoring small variable costs like processing fees that add up across volume.
- Loading up on fixed costs before sales are reliable enough to cover them.
FAQ
Are salaries fixed or variable?
Salaried pay is fixed, but hourly wages tied directly to production or shifts you can cut behave as variable costs.
Why does the mix matter for a startup?
Keeping costs variable early lets you shrink spending quickly if sales disappoint, protecting cash while the model is still unproven.