The revenue left over after subtracting the variable costs of serving a customer — the portion of every sale that contributes towards covering fixed costs and generating profit.
Contribution margin (%) = ((revenue − variable costs) ÷ revenue) × 100
A plan bills £120/mo per customer. Monthly variable costs per customer: £9 hosting, £4.20 Stripe fees, and £7.80 support and third-party API fees — £21 in total.
(£120 − £21) ÷ £120 × 100 = £99 ÷ £120 × 100 = 82.5% contribution margin, with each customer contributing £99/mo towards fixed costs and profit
Contribution margin counts only the costs that scale with each additional customer. For a Stripe-billed SaaS that means usage-driven hosting, payment processing fees, ticket-driven support, per-customer onboarding hours, and per-seat or per-API-call vendor fees. Fixed costs like salaries, rent, and R&D are deliberately excluded, so the metric answers a specific question: what does the next customer earn us?
It is not the same as gross margin, and the confusion is expensive. Gross margin includes fixed costs allocated to COGS — baseline support staffing, infrastructure you would pay for anyway — so it measures the profitability of delivering the product. Contribution margin isolates the truly incremental cost of one more customer, so it measures the profitability of acquiring and keeping that customer.
The most common mistake is computing one blended number across the whole business. A single figure hides that self-serve customers might contribute 85% while high-touch enterprise accounts contribute 60%, which changes where your next pound of acquisition spend should go. Segment by plan, channel, and delivery model before acting on it, and take care not to misclassify fixed costs like salaried support staff as variable.
Contribution margin is the correct input for the rest of your unit economics. Calculating LTV on raw revenue overstates lifetime value, and it powers break-even analysis directly: fixed costs divided by contribution per customer gives the number of customers you need before the business covers itself. Early margins are often low or even negative — heavy first-year onboarding is normal — so watch the trend by cohort age, not the day-one figure.
Contribution margin tells you whether growth is self-funding. Every new customer either contributes cash towards your fixed costs or digs the hole deeper — and because it feeds LTV, CAC payback, and break-even maths, getting it wrong quietly corrupts every downstream decision on pricing, channel spend, and when to hire.
Fiscallion puts mature SaaS contribution margins at 70–80%, with self-serve and PLG products typically running 72–85% and high-touch enterprise models 58–72%; below 70% at maturity usually signals a structural cost or pricing problem.
Mature SaaS businesses typically land at 70–80%, with self-serve products often reaching 72–85% and high-touch enterprise models running 58–72%. Early-stage companies frequently sit lower — or negative — because onboarding and support costs are front-loaded, and that is normal.
Gross margin subtracts all cost of goods sold, including fixed allocations like baseline support salaries. Contribution margin subtracts only variable costs — the truly incremental cost of serving one more customer. Gross margin measures the profitability of delivering the product; contribution margin measures the profitability of acquiring and keeping a customer.
Yes. If variable costs exceed revenue — common in year one when onboarding and support are heavy — each new customer loses money before fixed costs are even considered. That is tolerable temporarily, but if cohorts do not turn contribution-positive as they mature, pricing or the cost structure needs fixing.
No. Contribution margin ignores fixed costs entirely. It shows what each sale contributes towards covering those fixed costs; profit is what remains after they are actually covered. A business can have an excellent contribution margin and still lose money if fixed costs outweigh total contribution.
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