QUICK ANSWER
Contribution margin is what is left from a sale after the costs that move with it: landed cost including freight and duty, payment and marketplace fees, your real blended shipping cost, the return rate on that product, and paid acquisition where the sale was bought. For an ecommerce seller it is more useful than gross margin, because those variable costs are a large share of the sale and gross margin ignores most of them.
What did peak season actually earn you?
Most stores answer that question with a revenue figure, because revenue is the number the dashboard puts in front of you and it is the number that feels like the result. It is also the number least able to answer the question, because a discount event moves revenue and margin in opposite directions by design.
The honest answer requires one calculation per product, and it is arithmetic rather than accounting. If you can read a bank statement you can do this. The reason most owners have not is not difficulty, it is that nobody has ever shown them which costs belong in the subtraction.
What is contribution margin for an ecommerce business?
It is the amount a single sale contributes toward your fixed costs and profit, after everything that varies with that sale has been taken out. The sequence below is the one that works for a store selling physical goods through a platform.
- Start with the price the customer actually paid, after any discount code.
- Subtract landed cost: the supplier invoice plus inbound freight, duty and any customs brokerage, divided across the units in the shipment.
- Subtract payment processing and marketplace fees on that transaction.
- Subtract your real outbound shipping cost, not what the customer was charged for shipping.
- Subtract an allowance for the return rate on that specific product, since a returned unit carries outbound cost, often inbound cost, and sometimes cannot be resold.
- Subtract acquisition cost where the sale was bought through paid traffic rather than earned.
What remains is the contribution. Run it on a product discounted 30% with paid traffic behind it and the answer is frequently negative, which means every additional unit sold makes the month worse while the revenue line posts a record.
Which costs belong in it, and which do not?
The test is whether the cost moves when you sell one more unit. Processing fees move. Shipping moves. Returns move. Advertising moves, if the sale was bought. Your rent does not move, your software subscriptions do not move, and your salaries mostly do not move, so none of those belong in a contribution calculation.
This is a deliberate exclusion and it is worth being clear about the limitation it creates. Contribution margin does not tell you whether the business is profitable. It tells you whether a particular sale, at a particular price, with particular traffic behind it, is worth making. Those are different questions and the second one is the one a discount decision actually turns on. A product with positive contribution and a business with negative profit can both be true at once, and the fix for the second is a different conversation.
Why does gross margin mislead at this time of year?
Gross margin subtracts cost of goods from revenue and stops. For a traditional retailer that is a reasonable approximation, because the remaining variable costs are small. For an ecommerce seller they are not small. Payment and marketplace fees, outbound shipping, returns and paid acquisition can together exceed the cost of the goods themselves on a discounted item.
The seasonal problem is that all four of those rise during a discount event at the same time. Fees rise with volume. Shipping rises because peak season surcharges apply and because free shipping thresholds are easier to clear at a discount. Returns rise, because gift purchasing and impulse purchasing both return at higher rates than considered purchasing. And acquisition cost rises sharply, because every advertiser in your category is bidding in the same two weeks. A gross margin figure calculated in October will overstate November’s reality on every one of those four counts.
What do you actually do with the number?
Three things. Set a discount ceiling per product and build the promotion inside it rather than deciding the discount first and discovering the margin later. Reallocate: discount the items with the most contribution room hardest and protect the ones that only work at full price, which is close to the opposite of the common instinct to discount whatever is not selling. And set a cutoff for paid acquisition per product, because a positive contribution before advertising can become negative with it.
One caution on the inputs. Every figure above rests on landed cost being real rather than the supplier invoice. If freight and duty are missing from your cost of goods, every margin number in the business is better than reality by whatever those two amount to, and a discount floor calculated on a wrong cost is simply a more confident wrong answer. Fix the landed cost first.
Do this before the weekend rather than after it. A contribution calculation run in December tells you what happened. The same calculation run in the second week of November tells you what to price.
A last point on what the number cannot settle. Contribution margin treats every sale as equivalent, and some are not. A discounted first order that brings in a customer who buys three more times at full price is worth more than the contribution on that single transaction suggests, and a deep discount aimed at existing buyers who would have paid full price is worth less. If you have reliable repeat-purchase data by acquisition channel, use it to adjust. If you do not, and most stores do not, treat the contribution figure as the floor rather than the whole answer and be honest with yourself about which promotions are genuinely acquiring customers and which are discounting demand you already had.
Frequently asked questions
What is the difference between contribution margin and gross margin?
Gross margin subtracts only cost of goods. Contribution margin also subtracts the other costs that move with each sale: payment and marketplace fees, real shipping, returns and paid acquisition. For an ecommerce seller the gap between the two is usually large.
Should fixed costs be included?
No. Rent, salaries and software do not change when you sell one more unit, so including them answers a different question. Contribution margin is a pricing and promotion tool, not a profitability measure.
How do I calculate the return allowance?
Use that product’s own historical return rate rather than a store average, because rates vary enormously by category. Multiply the rate by the full cost of a returned unit, which includes outbound shipping, return shipping where you pay it, and any unit that cannot be resold.
What if I do not know my landed cost?
That is the first thing to fix, and it is more valuable than any margin analysis built on top of it. Landed cost is the supplier invoice plus inbound freight, duty and brokerage, allocated across the units received.
NEXT STEP
Transcounts builds landed cost and contribution margin into the monthly close for Canadian Shopify and Amazon sellers, so the figures are current rather than reconstructed. The $99 Ecommerce Diagnostic reviews your current books and reports within seven business days on what would need to change before these numbers could be trusted. The fee is credited against onboarding.
