Calculate contribution margin by product and channel

Direct answer

Contribution margin is net sales minus variable costs. For each product and channel, deduct sold-unit cost, fulfillment, shipping, and transaction fees. Show returns and directly attributable ad spend separately so the reader can see how each changes the result. Keep fixed overhead outside this measure.

Why this question comes up

One channel can sell more units but leave less per order after fees and shipping. Consistent cost rules make product and channel comparisons useful.

Records to gather

• Order revenue, discounts, shipping charged, and refunds by SKU and channel
• Landed unit cost including freight and duty
• Channel-specific fees: marketplace commission, payment processing, fulfilment
• Shipping cost actually incurred versus shipping revenue collected
• Returns and refunds by SKU and channel
• Directly attributable ad spend, if comparing contribution after marketing

Review workflow

1. Start with net sales. Subtract discounts and refunds from product sales. Include shipping charged to customers as revenue if it is not already in net sales.
2. Use the cost of units sold. Apply the inventory-cost method used in the books, including allocable inbound freight and duty where appropriate. Do not deduct the purchase cost of unsold inventory.
3. Assign channel costs. Deduct marketplace commission, payment processing, pick-and-pack, and carrier charges for the channel that incurred them.
4. Handle returns consistently. Include refunds once in revenue and add actual return shipping, handling, and any nonrecoverable product cost. A resalable returned unit is not automatically a full product-cost loss.
5. Show marketing separately. If ad spend can be attributed reliably, report contribution before and after that spend. Do not imply every campaign dollar varies with each order.
6. Keep fixed overhead out. Rent and other fixed costs belong in a separate profitability view, not the per-order contribution calculation.

What a useful answer should include

• Contribution margin per SKU and per channel, in currency and percent
• Net product revenue and shipping charged, with discounts and refunds counted once
• Landed cost per unit with components visible
• Channel fees attributed to their own channel
• Customer shipping revenue and carrier cost shown separately
• Contribution before and after attributable ad spend, if available
• A clear line marking what is excluded as fixed cost

Common failure modes

• Blending channels. A profitable direct store can mask a marketplace channel losing money on every order.
• Using supplier price as cost. It flatters every margin in the analysis.
• Double-counting a return. A refund reduces revenue; charge only additional return costs and any nonrecoverable unit cost.
• Allocating fixed overhead into contribution. It stops being contribution margin and can no longer answer the incremental question.