Contribution Margin

Contribution margin is the dollars each unit sold contributes toward covering fixed costs after variable costs are paid. It's the number that tells you whether selling more of a SKU makes you more money or just makes you busier.

Definition

Contribution margin is the difference between selling price and variable costs, expressed either as a dollar amount per unit or as a percentage of revenue. It measures how much each additional sale contributes to fixed costs and profit.

Two products can have the same gross margin but very different contribution margins, because gross margin includes only product cost while contribution margin includes the variable selling costs: marketplace fees, fulfillment, advertising, returns.

The formula

Contribution margin per unit = Selling price - Variable cost per unit

Contribution margin % = (Selling price - Variable cost per unit) / Selling price

Variable cost per unit includes everything that scales with each sale: variable COGS (manufacturing, freight, tariffs, fulfillment), marketplace referral fees, payment processing, advertising allocation, and a returns reserve.

Why ecommerce sellers need this view

A traditional gross margin calculation for a product selling at $24.99 with $6.50 COGS shows a 74% margin. Looks great. The ecommerce-adjusted contribution margin tells a different story.

That same product sold on Amazon FBA pays a 15% referral fee ($3.75), an FBA pick-pack fee ($4.20), and absorbs a $2.10 advertising allocation per unit at the current ACoS. After variable costs, the contribution margin per unit is $8.44, about 34%. Still profitable, but not 74% profitable. The difference is where the company makes its real margin decisions.

What contribution margin tells you

• Whether a SKU should stay or be discontinued. If contribution margin is negative, each sale costs you money.
• How much ad spend is rational on each SKU. Your maximum profitable cost-per-acquisition is bounded by the contribution margin.
• Which channel mix to push. The same product can have very different CM by channel.
• Whether a price increase is worth it. A 5% price increase often lifts CM by 15-20% because fixed variable costs don't change.

How ConnectBooks shows contribution margin

ConnectBooks calculates contribution margin per SKU per channel automatically. The SKU-level P&L view shows the per-unit and aggregate CM, breaks down each variable cost layer, and surfaces SKUs where CM is trending down before they cross into negative territory.

Related terms

• Gross margin: Revenue minus COGS only, no variable selling costs.
• Variable COGS: The product-cost portion of variable cost.
• Operating margin: Contribution margin minus fixed costs as a percentage of revenue.
• Break-even units: Fixed costs / contribution margin per unit.

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Running an e-commerce business comes with plenty of challenges, but ConnectBooks is here to make your life easier. With real-time insights, seamless integrations, and detailed tracking of your profitability and inventory, you can stay ahead of the game. Whether you’re selling on Amazon, Shopify, Walmart, TikTok or eBay, ConnectBooks helps you manage your finances with 100% accuracy and confidence, so you can focus on growing your business.

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