Updated
Contribution margin % = (revenue − variable costs) ÷ revenue × 100
Contribution margin is the amount left from a sale after subtracting only the variable costs tied to that sale, leaving the portion available to cover fixed costs and, beyond that, profit. The formula is: Contribution Margin = Revenue - Variable Costs, and it is often expressed as a percentage: Contribution Margin % = (Revenue - Variable Costs) / Revenue x 100.
Examples use made-up numbers. Education only, not tax, legal or investment advice.
The setup
Illustrative example: a service business charges $200 per appointment.
Variable costs (technician pay tied to that job, supplies, fuel) total $120.
Contribution margin is $80 per appointment, or 40%.
The math
If monthly fixed costs (rent, salaried office staff, insurance) are $8,000, the business needs 100 appointments ($8,000 / $80) to break even before any appointment generates profit.
Owner question to ask: "Which of my service lines has the highest contribution margin, and am I spending my limited crew hours on those first?" Two services can have identical revenue but very different contribution margins once variable cost differences are isolated.
Unique caveat: contribution margin only isolates variable costs, so it should not be confused with gross margin, which may bundle some costs differently depending on bookkeeping choices. It also assumes costs classified as "variable" truly scale with volume — a cost that is technically fixed in the short run (like a salaried crew lead) can distort the calculation if mislabeled as variable. Because contribution margin ignores fixed costs entirely, a high contribution margin on a single job does not by itself mean the overall business is profitable; it must be compared against total fixed costs for the period.
This definition is educational and does not replace advice from a licensed accountant or tax professional familiar with your specific books. Owners should confirm treatment with their bookkeeper before using this figure in a loan application, valuation, or tax filing. Small differences in chart-of-accounts setup can change how this number is calculated, so consistency period over period matters more than precision in any single month.
Continue with the full explainer lesson.
Definition source
SBA — Break-even point defines break-even as total revenue equaling total cost, and explains contribution margin as sale price less variable cost (or that difference divided by sale price for its percentage).
Questions owners ask
Is contribution margin gross margin?
Not necessarily. Contribution deducts variable costs, while gross margin deducts accounting cost of goods sold.
What does contribution per unit show?
Unit price less unit variable cost shows what one sale contributes toward fixed costs.
How does contribution relate to break-even?
Fixed costs divided by positive contribution per unit gives exact break-even units.