Gross Margin vs. Contribution Margin vs. Net Margin, Explained for Ecommerce

The three definitions

• Gross margin = (Revenue − COGS) ÷ Revenue. Answers: "how much room do I have before any other costs?" Doesn't account for marketplace fees, shipping, or advertising — a healthy-looking gross margin can still be an unprofitable product once those are included.
• Contribution margin = (Revenue − all variable costs including COGS, fees, shipping, and variable ad spend) ÷ Revenue. Answers: "what does this specific sale actually contribute toward fixed costs and profit?" This is the number that should drive per-SKU pricing and go/no-go decisions — see The Full Cost Stack of a Marketplace Sale.
• Net margin = (Revenue − all costs, including fixed costs like salaries and rent, allocated across all sales) ÷ Revenue. Answers: "is the business as a whole profitable?" Useful at the company level, not useful for deciding whether one specific SKU or one specific marketplace is worth pursuing.

Side-by-side comparison

Worked example: same sale, three numbers

A $30 sale, landed cost $9, marketplace fees + fulfillment $9.70, ad spend $3.60, and — allocated at the company level — $4.00 of fixed overhead per unit sold on average.

• Gross margin = ($30 − $9) ÷ $30 = 70%
• Contribution margin = ($30 − $9 − $9.70 − $3.60) ÷ $30 = $7.70 ÷ $30 = 25.7%
• Net margin = ($30 − $9 − $9.70 − $3.60 − $4.00) ÷ $30 = $3.70 ÷ $30 = 12.3%

All three numbers describe the exact same sale — the 58-point spread between the 70% gross margin and the 12.3% net margin is entirely a matter of which costs are included, not a calculation error.

Why this distinction causes real mistakes

A seller who prices based on gross margin alone (ignoring fees, shipping, ads) can launch a product that looks profitable on paper and loses money in practice. A seller who evaluates a new marketplace or SKU using company-wide net margin (which includes fixed costs unrelated to that specific decision) can wrongly reject a genuinely profitable opportunity because it's being penalized for overhead it didn't cause.

A related trap: allocating fixed overhead unevenly. If the $4.00 of overhead in the example above is a company-wide average but this particular SKU actually consumes far less operational attention than an average SKU, penalizing it with the average overhead figure understates its true value to the business — this is exactly why contribution margin, not net margin, is the right lens for a single-SKU decision.

The practical rule

Use contribution margin for per-SKU and per-channel decisions (should I sell this on this marketplace, at this price, with this ad spend). Use net margin only for whole-business health checks, not individual product decisions. Use gross margin as a fast initial sanity check before doing the fuller contribution-margin math — useful for quickly ruling out an obviously bad idea, not for approving a good one.

Best practices

• Always label which margin you're quoting when discussing numbers with a partner, investor, or accountant — "40% margin" is ambiguous and has caused real miscommunication between people using different definitions.
• Build contribution margin into your standard per-SKU reporting, not just gross margin — gross margin alone hides fee and ad-spend problems.
• Recalculate net margin periodically at the whole-business level, but never use it to approve or reject an individual product or channel decision.

Mistakes

• Quoting "margin" without specifying which of the three definitions is meant.
• Using gross margin to greenlight a new SKU or marketplace without ever calculating contribution margin.
• Using net margin (with allocated fixed costs) to judge a single SKU's worth, which can unfairly penalize otherwise-healthy products.

Checklist

• Know which margin figure any given report or conversation is referring to.
• Contribution margin is calculated and tracked per SKU, not just at the company level.
• Net margin is used only for whole-business decisions, never single-SKU ones.

FAQs