Contribution margin is price minus variable costs: what one more sale adds. The formula, a worked example and why gross margin misleads decisions.
By Sergey BruhPublished 6 min read
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The break-even point is the volume where contribution covers fixed costs. The formula, a monthly worked example and the margin of safety.
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Contribution margin is what one sale leaves after the costs that come with it: price minus variable costs. It answers one narrow question, what does one more unit add, and that makes it the number to use for most product decisions: which plan to promote, how deep a discount can go, whether a new format pays. The contribution margin ratio is the same thing as a share of the price. Gross margin, the line on a P&L, answers a different question about the company as a whole, and its cost groupings can move for reasons that have nothing to do with a single sale. Below: the formula, a worked example on lesson packages, and where gross margin leads a decision astray.
where is the price per unit and the variable costs per unit: the costs that grow when you sell one more. Multiply by units sold to get the contribution of a month.
What counts as variable depends on the business. For an online lesson it is the tutor's payout, the payment fee and the video bill. For a SaaS seat, usage-based hosting and AI inference. For a physical product, materials and delivery. Salaries, rent and the marketing budget stay out on purpose; spread them over units and the "cost per unit" changes with volume, see fixed vs variable costs.
Klasna is an online tutoring school. Families buy English lessons in packages of 8, 16 or 32; the bigger the package, the cheaper each lesson. In the 16-lesson package a lesson costs 9,920 ÷ 16 = 620 UAH. The tutor gets 390, the payment provider keeps 2.5% (15.50) and video and AI cost 30:
The ratio is 184.50 ÷ 620 = 29.76%: about 30 kopiykas of every hryvnia a family pays are left for fixed costs and profit.
Look where the 32-pack's 40-hryvnia discount went. The tutor still gets 390 and video still costs 30; only the fee shrank, by one hryvnia. The other 39 came straight out of contribution margin: 145.50 instead of 184.50.
The CEO wants a September campaign for the 32-pack: 4,656 per package beats 2,952. Compared with what?
Contribution margin per unit tells you the size of each option; the decision depends on what the customer would have done without the offer. That is the question to take to the data.
Gross margin is (revenue − cost of revenue) ÷ revenue, a line on the P&L. Which costs land in "cost of revenue" is an accounting grouping. It often includes delivery costs that don't change with one more sale (a support team, platform licences) and often leaves out variable costs such as payment fees, which go into operating expenses.
Take one such grouping for Klasna's lesson sales: tutor payouts, video and AI and the support coordinators in cost of sales, payment fees below the line.
In March: (4,868,640 − 3,136,000 − 243,040 − 114,000) ÷ 4,868,640 = 28.25%. In July: (1,627,600 − 1,047,800 − 80,600 − 76,000) ÷ 1,627,600 = 26.00%. Gross margin "fell" by more than two points, yet each lesson earned slightly more. The drop is the coordinators' fixed cost spread over a quiet month. Anyone pricing a summer offer off that gross margin would be reacting to volume, not to the economics of a lesson.
Gross margin is still useful for comparing companies and periods. For a decision about units, use contribution margin.
No. Contribution margin subtracts only the costs that grow with each unit. Gross margin subtracts the P&L's cost of revenue, which can include fixed delivery costs and leave out variable ones like payment fees.
Yes, when a unit costs more to deliver than it brings, like a group session with too few learners. Every such sale makes the month worse.
There is no universal number. Compare it with your fixed costs: the ratio tells you how much revenue you need to cover them.
The lesson Contribution margin: what one lesson leaves works through Klasna's full price list with numeric exercises checked instantly, and the case should Klasna launch group lessons? uses contribution margin to judge a real pilot. Both are part of the course Finance for Product People: From Unit Economics to Business Cases.
