Gross margin is the number most store owners know. It is also the one most likely to mislead them.
A product with a 60% gross margin sounds healthy. But by the time you have shipped it, packed it, paid the card fees and absorbed the returns, a large part of that margin is gone. What is left is the contribution margin, and it is the number that tells you whether an extra order actually makes you money.
What contribution margin is
Contribution margin is revenue minus every variable cost, meaning every cost that rises and falls with the number of orders.
It is called contribution because it is what each order contributes toward your fixed costs. Once fixed costs are covered, every additional dollar of contribution is profit.
That makes it the most useful margin for day-to-day decisions. Pricing, discounting, free shipping thresholds, ad budgets and product mix all come down to the same question: what does this do to contribution?
The contribution margin formula
You can calculate it for the whole business over a period, for a single order, or for a single unit of a product.
Per order, using your average order value:
Per unit, for product-level decisions:
A product that sells for $40 with $22 of variable cost per unit has a contribution margin of $18 per unit.
The contribution margin ratio
The ratio expresses contribution as a share of revenue, which makes it easy to compare products, channels and time periods of different sizes.
The $40 product above has a ratio of $18 ÷ $40 = 45%. For every dollar of that product you sell, 45 cents goes toward fixed costs and profit.
The ratio is also the number that sets your advertising limits. Your break-even ROAS is simply 1 divided by the contribution margin ratio before ad spend.
What counts as a variable cost in ecommerce
The formula is simple. The hard part is being honest about what goes into variable costs. For a typical online store, include:
- Cost of goods sold. The landed cost of the product, including inbound freight and duties.
- Outbound shipping. What you pay the carrier, minus anything the customer paid you for shipping.
- Fulfillment. Pick and pack fees, packaging, inserts and labels, whether in-house or through a 3PL.
- Payment processing. Card and gateway fees, usually a percentage of the order plus a small fixed fee.
- Returns and refunds. Refunded revenue, return shipping and any stock you cannot resell.
- Marketplace and per-order platform fees. Commissions and apps that charge per order or per percentage of sales.
- Marketing, optionally. Ad spend scales with orders for most stores, so it is worth calculating contribution both before and after it.
Discounts are usually handled by using revenue after discounts, rather than listing them as a cost.
What does not belong here: salaries, rent, flat monthly software subscriptions and agency retainers. Those are fixed costs. They matter, but they do not change when you take one more order.
A worked example
Take a store with an $80 average order value. Each order carries:
| Variable cost | Per order |
|---|---|
| Product cost | $30.00 |
| Shipping and fulfillment | $9.00 |
| Payment processing (2.9%) | $2.32 |
| Returns and refunds (4% of revenue) | $3.20 |
| Other per-order costs | $2.00 |
| Total variable cost | $46.52 |
Contribution margin per order is $80.00 − $46.52 = $33.48, a ratio of 41.9%.
If the store spends $15 in advertising for every order, contribution after marketing drops to $18.48 per order, or 23.1%. That $18.48 is what each order actually leaves to pay for the team, the software and the rent.
These are the starting numbers in the calculator at the top of this page, so you can change any line and see what happens.
Contribution margin vs gross margin
Using the same order:
| Gross margin | Contribution margin | |
|---|---|---|
| Subtracts | Product cost only | All variable costs |
| Per order | $80 − $30 = $50.00 | $80 − $46.52 = $33.48 |
| Ratio | 62.5% | 41.9% |
Gross margin says this order keeps 62.5 cents of every dollar. Contribution margin says it keeps 41.9 cents before marketing. That gap of more than 20 points is shipping, fulfillment, fees and returns, and it is exactly the gap that makes profitable-looking promotions and ad campaigns lose money.
Gross margin is still worth tracking, because it isolates product pricing and sourcing. But contribution margin is the one to make decisions with.
CM1, CM2 and CM3
Many ecommerce teams break contribution margin into layers so they can see where margin goes. Naming conventions vary between companies, but a common version is:
- CM1: revenue minus cost of goods. This is gross margin by another name.
- CM2: CM1 minus shipping, fulfillment, payment processing and returns. This is contribution before marketing.
- CM3: CM2 minus marketing and advertising. This is what the order leaves after it has been acquired.
Layering the numbers this way shows you which cost is doing the damage. A falling CM2 points at operations: shipping rates, packaging, returns. A falling CM3 with a steady CM2 points at acquisition costs.
The contribution margin income statement
A standard income statement mixes fixed and variable costs together. A contribution margin income statement separates them, which shows you directly how profit responds to volume.
Using the example store at 1,000 orders a month:
| Monthly | |
|---|---|
| Revenue (1,000 orders × $80) | $80,000 |
| Variable costs (1,000 × $46.52) | −$46,520 |
| Contribution margin (CM2) | $33,480 |
| Marketing | −$15,000 |
| Contribution after marketing (CM3) | $18,480 |
| Fixed costs | −$14,000 |
| Operating profit | $4,480 |
Laid out this way, the leverage is obvious. Each additional order adds $33.48 of contribution, less whatever it costs to acquire. The fixed costs are already paid for.
What is a good contribution margin?
There is no universal benchmark, because it depends on category, price point, shipping weight and business model. A brand selling high-margin consumables will look nothing like a retailer of heavy, low-margin goods.
The more useful test is whether your contribution margin supports the way you grow:
- If you rely on paid acquisition, your contribution before marketing sets your break-even ROAS. A 25% ratio needs a 4x return just to break even. A 50% ratio needs 2x.
- Your contribution after marketing, across all orders, has to cover fixed costs with room to spare. If it only just covers them, any wobble in conversion or ad costs puts the business into a loss.
- Product-level contribution should be positive for everything you actively promote. It is common to find a handful of SKUs, often the heavy or frequently returned ones, that lose money on every sale.
Track the trend at least monthly. A slowly falling contribution margin is one of the most common reasons revenue grows while profit does not, and it is covered in more depth in where ecommerce margins quietly disappear.
How to improve contribution margin
Every improvement falls into one of three groups: charge more per order, spend less per order, or lose less per order.
Raise average order value. Many costs are charged per order, not per dollar. Pick and pack, packaging and the fixed part of the shipping rate barely change when the basket gets bigger, so a higher AOV spreads them thinner. Bundles, thresholds and considered recommendations are the usual tools. See AOV optimization.
Set a free shipping threshold with the math, not the competition. Free shipping on a $25 order can wipe out its contribution entirely. Set the threshold where the contribution of the order covers the shipping you are absorbing.
Discount less, and more deliberately. Discounts come straight out of contribution. They are covered below, and in why discounts rarely create profit.
Reduce returns. Better sizing information, product photography and accurate descriptions are margin projects, because every return costs you shipping twice and sometimes the product.
Renegotiate the per-order costs. Carrier rates, 3PL fees, packaging suppliers and payment processing rates can all be revisited once you have volume. Check the apps you pay per order, too. It adds up, as covered in how app sprawl hurts profitability.
Improve the product mix. Promote the products with the highest contribution per order, not the highest revenue. Your best seller by revenue is not always your best seller by profit.
Using contribution margin to judge a discount
Here is the decision where contribution margin earns its keep. Take the $80 example order, which contributes $33.48, and offer 20% off.
The order now brings in $64. Product, shipping and other per-order costs stay at $41, and the percentage costs fall a little to $4.42. Total variable cost is $45.42, so contribution per order drops to $18.58.
To earn the same total contribution as before, you need $33.48 ÷ $18.58 = 1.8 times as many orders. The promotion has to lift orders by 80% just to break even.
A 20% discount sounds modest. Measured on gross margin it looks affordable. Measured on contribution, it needs a very strong response to pay for itself. This is why the calculator matters: run the numbers before the promotion, not after.
Put it to work
Start with the calculator at the top of this page, using your real averages for the last 90 days. Then calculate it once more for your five best-selling products individually.
Most store owners who do this for the first time find at least one surprise: a product, a channel or a shipping rule that has been quietly losing money on every order. Fixing that is often the fastest profit improvement available, because it requires no new customers at all.