Contribution margin is revenue minus variable costs. It tells you what each sale contributes toward covering your fixed costs, and once those are covered, toward profit.
Contribution margins are the right tool for product-level decisions in a way that overall profitability is not. A business average tells you whether the whole operation works. Contribution margin tells you whether a specific item, order or customer is worth having, which is the question behind every pricing decision, every discount request and every “should we keep selling this”.
The Bottom Line
- Contribution margin = revenue − variable costs. Per unit, it is price − variable cost per unit.
- Contribution margin ratio = contribution margin ÷ revenue. Use the ratio to compare products of different prices.
- It differs from gross margin by which costs count as variable. Delivery and commission are variable and often excluded from gross margin.
- Fixed costs ÷ contribution margin per unit = your break-even volume.
- A product with a positive contribution margin can be worth keeping even when it looks unprofitable on a fully loaded basis.
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The contribution margin formula
Contribution margin = revenue − variable costs
Contribution margin per unit = selling price − variable cost per unit
Contribution margin ratio = contribution margin ÷ revenue × 100
Variable costs are the ones that exist only because you made the sale. Materials, ingredients, packaging, the commission on the transaction, the card fee, and for anyone shipping goods, the delivery cost attributable to that order.
Fixed costs are the ones that carry on regardless: rent, insurance, salaried staff, software, the lease on the van. They do not belong in a contribution margin calculation, which is exactly what makes the metric useful for decisions at the margin.
A worked example. You sell a hamper at £45. Contents cost £19, packaging £3, card fee £1.10, and the delivery attributable to it is £6.
Contribution margin per unit is £45 − £29.10 = £15.90. The ratio is 15.90 ÷ 45 = 35.3%.
So every hamper sold puts £15.90 toward your fixed costs. Sell enough of them and the fixed costs are covered; everything after that is profit.
Contribution margin against gross margin
The two get conflated constantly, and the difference is which costs you classify as variable.
Gross margin deducts cost of goods sold, which conventionally means the direct cost of producing the product. Contribution margin deducts all variable costs, which includes several things cost of goods sold usually leaves out: sales commission, payment processing, and most significantly for a delivery business, the cost of getting the order to the customer.
| Gross margin | Contribution margin | |
|---|---|---|
| Deducts | Cost of goods sold | All variable costs |
| Includes delivery cost | Usually not | Yes |
| Includes commission and card fees | Usually not | Yes |
| Best used for | Business-level health, reporting | Pricing, product mix, break-even |
| Typical level | Higher | Lower |
Sector context helps when you are judging whether your own variable costs sit in a normal range. Average restaurant profit margins and how to improve them is useful for any food business, since food cost and labour are the two largest variable lines, and four strategies for grocery store profit margins covers the same problem where stock turns faster and margins are thinner still.
That delivery line is the reason the two can tell opposite stories. A product with a healthy 40% gross margin and a £7 delivery cost on a £28 order has a contribution margin closer to 15%. If you are judging product decisions on gross margin alone, you are systematically overestimating your least convenient orders, and the effect is strongest on small orders travelling furthest.
This is also the connection to the profit margin benchmarks for small businesses: the business-level net margin is the outcome, and contribution margin is where you can actually intervene.
Break-even, which is the metric’s most useful output
Break-even volume = total fixed costs ÷ contribution margin per unit
With £6,400 a month in fixed costs and £15.90 of contribution per hamper, break-even is 6,400 ÷ 15.90 = 403 hampers a month. Below that you lose money, above it you make £15.90 a unit.
This single calculation reframes a lot of decisions.
It prices discounts honestly. Dropping the hamper to £40 cuts contribution to £10.90, and break-even rises from 403 to 588 units. A 11% price cut requires 46% more volume to stand still. Most discount decisions would not survive this arithmetic being done first.
It sizes the cost of a fixed-cost increase. A £900 monthly rent rise needs 57 more units a month. Knowing that converts “can we afford the bigger unit” into a sales target.
It tells you what a price rise is worth. At £48 instead of £45, contribution goes to £18.90 and break-even falls to 339 units. You could lose 16% of volume and be no worse off.
Using contribution margin to decide what to push and what to drop
Rank every product by contribution margin per unit and by ratio, then look at the two rankings together.
High ratio, high volume. The business. Protect it, make sure it never goes out of stock, and resist discounting it.
High ratio, low volume. The opportunity. Something earning well per sale and selling rarely is usually a marketing problem rather than a product problem, and it is the cheapest growth available because you already stock it.
Low ratio, high volume. The trap, and the most common finding. A popular item earning very little, often kept on the theory that it draws people in. Sometimes true, and worth testing rather than assuming: check whether customers buying it also buy anything else. Frequently they do not.
Low ratio, low volume. The candidate for removal. It occupies stock, attention and shelf space for little return.
Negative contribution margin. Stop, immediately. Every sale of this item makes you poorer, and selling more makes it worse. Raise the price or delist it.
A caution on the per-unit versus ratio distinction. Ranking only by ratio favours cheap items with proportionally low costs; ranking only by per-unit figures favours expensive ones. A £6 item at a 60% ratio contributes £3.60, while a £70 item at 25% contributes £17.50. If your constraint is shelf space or van capacity, the per-unit figure matters more. If your constraint is cash tied up in stock, the ratio matters more.
Contribution margin per order and per customer
The same arithmetic applied one level up, and for anyone who delivers this is where it earns its keep.
Contribution margin per order = order value − variable costs of that order, including the delivery
Run this across a month of orders and the distribution is usually revealing. There is normally a tail of orders with negative contribution: small baskets going to distant addresses, where the delivery cost exceeds the margin on the goods entirely.
That tail is the argument for a minimum order value or a delivery threshold, and contribution margin per order is how you set the number rather than guessing it. The threshold belongs at the order size where contribution turns positive with a sensible buffer. Encouraging larger baskets is the other side of the same coin: because delivery cost per stop is close to fixed, a bigger order at the same address converts almost directly into contribution.
Per customer, the calculation answers whether an account is worth keeping. A customer ordering frequently in small amounts across a wide area can generate meaningful revenue and negative contribution, and that only ever becomes visible at this level of detail.
Two cautions before acting on it. First, dropping a customer or a product is a decision with sentiment consequences, so it is worth seeing whether the affected customers are ones who would otherwise recommend you, your net promoter score responses will tell you who those people are. Second, check the cash timing: low-contribution customers who pay promptly can be more useful than high-contribution customers who pay at ninety days, which is a point about the cash conversion cycle rather than about margin.
Getting the variable cost classification right
The calculation lives or dies on this, and two errors do most of the damage.
Treating a fixed cost as variable. The commonest version is allocating a share of rent or salaried wages to each unit. That produces a fully loaded cost, which is a legitimate number for other purposes and the wrong one here, because it makes marginal sales look unprofitable when they are not. If you would pay it anyway with the sale or without, it is fixed.
Treating a variable cost as fixed. The mirror error, and in a delivery business it is usually the delivery itself. Vehicle depreciation and insurance are fixed; fuel, driver hours and mileage attributable to a route are not. Treating the whole delivery operation as overhead makes every product look better than it is.
Some costs are mixed, a van with fixed finance and variable fuel, staff on a basic plus commission. Split them rather than forcing a category. Rough splits are fine; the direction of the answer rarely depends on the last few percent.
Before committing to equipment or capacity meant to improve contribution, run it as an ROI calculation using contribution margin as the per-unit gain, which is the correct input because it is the amount each additional sale actually adds.
Where contribution margin fits with your other numbers
Contribution margin is a decision metric, not a performance metric. You would not report it to a lender, and you would not use it to judge whether last quarter was good. Its job is to answer specific questions: what should this cost, is this worth selling, how many do we need to sell.
It pairs with growth. The growth worth having is growth in total contribution, not in revenue, and the two diverge whenever expansion comes from lower-contribution lines or longer delivery routes. Watching contribution alongside the revenue growth metrics is what catches that.
It sits in the profit group of the small business metrics worth tracking, and it is the member of that group most owners have never calculated.
Frequently asked questions
What is contribution margin?
Revenue minus variable costs. It is the amount each sale contributes toward fixed costs, and toward profit once fixed costs are covered.
How do you calculate contribution margin?
Subtract variable costs from revenue. For a single unit, subtract the variable cost per unit from the selling price. For the ratio, divide the contribution margin by revenue and multiply by 100.
What is the difference between contribution margin and gross margin?
Which costs are deducted. Gross margin removes cost of goods sold; contribution margin removes all variable costs, which typically includes delivery, commission and payment fees that cost of goods sold leaves out. Contribution margin is therefore usually the lower figure and the more useful one for pricing.
What is a good contribution margin?
High enough that your expected volume covers fixed costs with room to spare, which makes it a business-specific answer rather than a benchmark. The universal rule is narrower: a negative contribution margin is never acceptable, because each additional sale increases the loss.
Can a product with a low contribution margin be worth keeping?
Yes, if it is positive and it brings in sales of other things. The test is whether customers who buy it also buy higher-contribution items. If they do, it earns its place; if they buy it alone, it does not.
Where to start
Take your five best-selling products and calculate contribution margin per unit for each, being careful to include delivery, packaging and payment fees. The exercise takes an hour and very often turns up one line earning far less than assumed.
Then run the break-even calculation on your fixed costs. Knowing the volume you need is the number that makes every subsequent pricing and discount conversation shorter.
