Contribution Margin: The Unit Economics Number Founders Skip
Contribution margin is what each sale leaves after variable costs. It tells you whether growth helps or hurts, and it is the base of sound unit economics.
- Formula
- Revenue minus variable costs, per unit or in total
- Why it matters
- Shows how much each sale contributes to fixed costs and profit
- Common mistake
- Using gross margin and ignoring shipping, fees and ad costs
15+ years in finance: 100+ financial models built, €40m+ raised for clients, Forbes contributor and lecturer.
Short answer: contribution margin is what a sale leaves after the costs that rise and fall with it. If it is positive and large enough, each sale helps pay your fixed costs and then becomes profit. If it is thin or negative, growth makes things worse.
The formula
Contribution margin = revenue minus variable costs.
You can calculate it per unit, per order, per customer or for the whole business. As a percentage: contribution margin divided by revenue.
Variable costs usually include:
- Cost of goods or direct delivery cost
- Payment processing fees
- Shipping and fulfilment
- Sales commissions
- Advertising or acquisition cost tied to the sale
A simple worked example
Illustrative numbers only:
| Item | Per order |
|---|---|
| Selling price | 100 |
| Product cost | 40 |
| Shipping and packaging | 12 |
| Payment fees | 3 |
| Advertising cost per order | 25 |
| Contribution margin | 20 |
Gross margin looks like 60 percent here, since only product cost is deducted. Contribution margin is 20 percent. That gap is where many founders get surprised.
Why it matters more than gross margin
Gross margin tells you about production efficiency. Contribution margin tells you whether a sale is worth making. It is the number to use for:
- Pricing: a discount that looks small can wipe out most of the contribution.
- Channel decisions: two channels can have the same revenue but very different contribution once fees and ads are included.
- Break-even: divide fixed costs by contribution per unit to see how many units you must sell. See Break-Even Analysis for Founders.
- Growth planning: if contribution is negative, spending more on growth increases losses.
Link to unit economics
Unit economics asks whether one customer or one order makes money. Contribution margin is the order-level version. For the customer-level version, compare lifetime value with acquisition cost, covered in LTV to CAC Ratio Explained.
Common mistakes
- Treating a cost as fixed when it moves with volume.
- Leaving out returns, refunds or discounts.
- Averaging across products with very different margins, which hides the losers.
- Calculating once and never updating after prices or fees change.
What to do next
List your variable costs for your top three products or channels, calculate contribution for each, and rank them. Decisions about what to push, reprice or stop usually become clearer within an hour. If the picture is unclear, Profit Margin Analysis is a useful next read.
This article is general information, not legal, tax or investment advice.
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Related questions
Is contribution margin the same as gross margin?
No. Gross margin subtracts only direct production or product costs. Contribution margin subtracts all variable costs, including payment fees, shipping and often marketing tied to the sale.
What is a good contribution margin?
It depends on the industry and on your fixed costs. The useful test is whether total contribution covers fixed costs with room left for profit.
Can contribution margin be negative?
Yes. Then every extra sale loses money, and growth makes the problem bigger.
