Contribution margin is the amount of revenue left after subtracting variable costs, which is available to cover fixed costs and generate profit. It is one of the most practical numbers in pricing and cost analysis because it shows exactly how much each sale contributes to the business.
The Formula
Contribution margin per unit = Selling price − Variable cost per unit
Contribution margin ratio (CM ratio) = Contribution margin ÷ Selling price
For example, a product that sells for $80 with variable costs of $30 per unit:
Contribution margin = $80 − $30 = $50 per unit CM ratio = $50 ÷ $80 = 62.5%
This means 62.5 cents of every dollar in revenue is available to pay fixed costs and profit.
Variable Costs vs. Fixed Costs
Variable costs change with each unit sold: materials, per-unit shipping, packaging, payment processing fees, sales commissions.
Fixed costs do not change based on volume: rent, salaries, insurance, software subscriptions.
Contribution margin analysis is built on this distinction. It answers: "After paying the costs that go up every time I sell a unit, how much is left?"
How It Connects to Break-Even
Once you know your contribution margin per unit, you can calculate how many units you need to sell to cover your fixed costs:
Break-even units = Total fixed costs ÷ Contribution margin per unit
If fixed costs are $10,000/month and contribution margin is $50/unit:
$10,000 ÷ $50 = 200 units per month to break even
Every unit sold above 200 generates $50 in pure profit.
Contribution Margin vs. Gross Profit
Contribution margin and gross profit are often confused because both subtract costs from revenue, but they use different cost categories.
Gross profit subtracts cost of goods sold (COGS), which is mostly variable but can include some fixed manufacturing overhead depending on accounting method.
Contribution margin subtracts all variable costs, regardless of whether they appear in COGS or operating expenses. Sales commissions, for example, are usually in operating expenses but are a variable cost that belongs in a contribution margin analysis.
Use gross margin for financial reporting. Use contribution margin for pricing and volume decisions.
Practical Uses
Pricing decisions: If a product has a negative contribution margin, you lose money on every unit sold. No amount of volume can make it profitable. A positive but thin contribution margin might still be acceptable if it helps cover fixed costs, but only if better options are not available.
Product mix decisions: When you have limited production capacity, prioritize products with the highest contribution margin per unit of the constrained resource (machine hours, labor hours, shelf space).
Discount analysis: Before offering a discount, check whether the lower contribution margin on each unit is offset by enough volume increase. A 20% price cut requires roughly a 33% increase in volume just to maintain the same total contribution.
Customer profitability: Applying contribution margin thinking to customer segments shows which types of customers are worth acquiring and retaining.
Limitations
Contribution margin analysis assumes costs are cleanly separable into fixed and variable. In practice, some costs are semi-variable (step costs that jump at certain volume thresholds, like hiring another employee). For strategic decisions, recognize that the fixed/variable distinction is a simplification, not a perfect description of reality.