Contribution Margin for E-commerce Businesses Explained

What is Contribution Margin?

Contribution is the amount left after variable costs. It contributes towards the costs you have to pay even when you sell nothing, then towards profit.

Contribution margin = sales revenue − variable costs.

Contribution margin percentage = contribution margin ÷ sales revenue × 100.

For a unit calculation, use the selling price and variable cost of one unit. A €100 sale with €65 of variable costs leaves €35 contribution, or 35%. Use prices excluding VAT and sales after discounts and refunds. Where purchase VAT is recoverable, exclude it from costs too; irrecoverable VAT remains a cost.

This is the standard cost-behaviour definition used in OpenStax’s managerial accounting guidance. Your own report should state which costs it includes. A number labelled contribution is not useful if the definition changes from month to month.

Why Focus on Contribution Margin?

Sales tell you how much customers bought. Gross margin tells you what remains after the cost of those products. Contribution tells you more about what serving those orders costs.

That matters when you are deciding whether to raise prices, stop a promotion, change a delivery offer or spend more on a channel. More sales help only if they bring enough contribution to pay for the extra work and leave something for the business.

Look at contribution by product and channel, alongside the total. A strong overall result can hide a product that loses money every time it ships. Equally, a lower-margin product may be worth keeping if it brings repeat customers who buy other profitable products. You need evidence of that behaviour, not an assumption that growth will fix the loss.

Calculating Contribution Margin

Start with a settled sales figure. A Shopify payout is not sales revenue: VAT, fees, refunds and other adjustments can sit between sales and cash received. Our Shopify accounting guide explains that reconciliation.

Then agree the cost layers. The illustration below uses €10,000 of net sales for one period. Product costs are assumed to vary with units sold. Fulfilment and payment fees vary with orders. Advertising is shown separately because a campaign budget does not necessarily move automatically with each sale.

Those are three different answers: 55% gross margin, 40% contribution before advertising and 20% after advertising. None should be presented as interchangeable. The €500 result also assumes the table includes all relevant operating costs; interest and tax are outside this illustration.

A sales-to-ad-spend ratio of five to one would sound encouraging here. It still leaves only €2,000 after the costs shown and before fixed overheads. It does not prove which channel caused the sales, either.

What Do You Include in COGS?

COGS means cost of goods sold. For a reseller, product cost normally starts with the cost of acquiring the goods and bringing them to their current location and condition. That can include inbound freight and duties. Buying stock is not the same as charging it all against this month’s sales: unsold stock remains stock, subject to the applicable valuation rules.

Our inventory accounting guide covers stock valuation and the movement from purchases to cost of sales.

Avoid double counting. If delivery or packaging is already in the cost figure you have deducted, do not deduct it again under fulfilment. If your accounts include fixed production costs in COGS, a strict variable-cost contribution calculation needs a separate cost analysis.

The practical question is simple: what did it cost to sell and fulfil these orders, and where is each cost recorded?

What Other Costs Belong in the Calculation?

Map the costs instead of taking a dashboard’s category names on trust.

Payment fees: include the actual charges, including fixed fees per transaction where applicable.

Fulfilment: separate the charge per order from a warehouse’s fixed monthly charge.

Packaging and shipping: use the costs for the destination and order size, not one convenient average if the mix changes.

Returns: reduce sales for refunds and include the associated handling costs. Account for recovered stock consistently so you do not charge its cost twice.

Advertising: show it as a distinct layer and agree how shared campaigns are allocated.

Some costs are mixed. A fulfilment provider may charge a monthly minimum plus a fee per order. A member of staff may handle extra orders until the volume requires another hire. The cost does not behave the same way at every level of sales.

Document the assumptions. They matter when a campaign or a new market changes the order mix.

Contribution Margin Ratio

The ratio lets you compare contribution with sales, but it does not remove the need to compare like with like.

If product A leaves €35 on a €100 sale and product B leaves €20 on a €50 sale, their ratios are 35% and 40%. B has the higher percentage; A leaves more euros per unit. Which is more useful depends on demand, capacity, acquisition cost and the cash tied up in stock.

Use both the euro amount and the percentage. A product can improve its percentage while total contribution falls because too few units sell.

For a simple break-even illustration, €7,000 of fixed costs divided by €35 contribution per unit means 200 units to break even. That assumes the price, variable unit cost and fixed-cost base stay unchanged, and that all costs are included once. A multi-product business needs to allow for its sales mix.

Contribution Margin vs Gross Margin

Gross margin deducts cost of sales. Standard contribution deducts variable costs, whether those costs sit inside or outside cost of sales in the accounts.

They can differ for two reasons: there are variable selling costs outside COGS, and COGS may contain fixed costs. That is why subtracting full COGS and then every variable cost can give the wrong answer.

For management decisions, a clearly defined contribution-after-advertising report is often useful. Keep its label and cost policy visible. Reconcile it to the accounts so that the useful management view does not become a second, contradictory version of profit.

Contribution Margin in Different Industries

The principle travels; the cost list changes. An online retailer needs product, shipping and transaction costs. An agency needs to understand delivery labour and subcontractors. A SaaS company needs to understand the costs of delivering and supporting its service.

A salaried team is not automatically a variable cost just because it delivers the work. Distinguish short-term spare capacity from the cost of adding capacity. The question behind the calculation is always which costs change with the activity you are considering.

Improving Your Margin

First fix the inputs. Before increasing ad spend, check one recent month’s sales, product costs, fees, fulfilment and refunds against the underlying records.

Then choose a specific action. A delivery promotion may need a minimum order value. A product may need a higher price. A channel may need a lower acquisition cost. A supplier negotiation may do more for profit than another campaign.

We are less interested in winning an argument about which platform owns a sale than in knowing what the sale leaves behind. Channel attribution can inform decisions, but it should not excuse a contribution report built on missing costs.

Use tools to make that review easier. The ecommerce growth webinar with StoreHero explores the wider commercial discussion. A tool can assemble the numbers; someone still has to check the data and decide what to change. Our ecommerce growth guide is another resource for the wider business review.