Contribution margin

Contribution margin measures the amount each unit of sale contributes toward covering fixed costs (and profit, after fixed costs are covered). Calculated as: Revenue - Variable costs. Variable costs include parts, materials, direct labor, subcontractor fees — anything that scales with the volume of service delivered.

Contribution margin is distinct from gross margin in important ways. Gross margin treats labor as a direct cost; contribution margin treats only the variable portion of labor (e.g., overtime, contracted) as variable, with salaried/baseline labor treated as fixed. The result: contribution margin per unit is usually higher than gross margin per unit.

When contribution margin matters: incremental decisions. Adding a service line, taking on an additional job at a given price, reaching a particular tier of bonus structure. The relevant question for incremental decisions is 'does this contribute toward fixed costs?' Contribution margin answers it. Gross margin can be misleading for these decisions because it treats some semi-fixed costs as if they scale with volume.

For service operators, contribution margin analysis is most useful when evaluating: pricing decisions on overflow jobs (the fixed costs are already covered; incremental jobs only need to clear variable costs to be profitable), seasonal expansion decisions, special project bidding. The break-even calculation — how much volume covers fixed costs — is built from contribution margin.