Contribution margin is the revenue remaining per customer or per unit after subtracting only the variable costs directly attributable to that customer or unit — not fixed costs. In SaaS, this means revenue minus the marginal costs of serving one more customer (additional hosting, per-customer API calls, per-customer support costs). It answers: "If I add one more customer, how much do they contribute to covering fixed costs and generating profit?"
Contribution Margin = Revenue per Customer − Variable Costs per Customer
Customer paying $99/month. Marginal hosting cost: $3. AI API cost per customer per month: $5. Per-customer support cost (averaged): $2.
$99 − ($3 + $5 + $2)
→ $89 contribution margin per customer per month (90%). Each new customer contributes $89 toward fixed costs and profit.
Contribution margin is the tool for scaling decisions. When evaluating whether to grow aggressively, contribution margin tells you how much each incremental customer adds to your ability to cover fixed costs. As long as contribution margin is positive, adding customers improves your operating position — even if the company is not yet profitable overall.
For pricing decisions, contribution margin reveals the economic floor. Discount thresholds, promotional pricing, and minimum viable plan prices should all be set above the contribution margin breakeven. Selling below variable cost is never rational. Selling above variable cost but below allocated fixed costs may be a deliberate early-market decision, but should be conscious.
As SaaS businesses scale, contribution margin should expand because fixed costs are shared over more customers. If contribution margin is not improving with scale, it indicates variable costs are growing proportionally — a sign of architecture or operational problems that worsen over time.
the mrrsucks take
Negative contribution margin means you pay to serve every customer you acquire. There is no scale at which this becomes profitable — it just becomes more expensive faster.
Gross margin subtracts all COGS from revenue — both fixed and variable delivery costs. Contribution margin subtracts only variable per-customer costs. In SaaS, the difference is primarily fixed infrastructure and CS salaries that are allocated across all customers but do not vary per individual customer.
No — contribution margin is always ≤ gross margin because gross margin includes the same variable costs plus additional fixed delivery costs. If your product has near-zero per-customer variable costs, contribution margin and gross margin converge.
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