PROFITFALCON How to Calculate Contribution Margin for E-commerce (Formula + Worked Example)
Gross margin tells you how the catalog is doing on average. Contribution margin tells you which SKUs are actually paying the bills — and which ones only look profitable.
Why gross margin isn't enough
Gross margin stops at cost of goods. It ignores payment fees, shipping subsidies, packaging, returns, and the ad spend it took to win the order. A SKU can carry a 60% gross margin and still lose money on every unit once those costs land.
Everything in that formula scales with volume. Fixed costs (rent, salaries, software) stay out — that's the point. Contribution margin answers one question: when you sell one more unit, does cash go up or down?
Worked example (sample numbers)
Take a candle priced at $34 with 1,200 units sold in a month:
- Revenue: $40,800
- COGS at $9.20/unit: −$11,040
- Payment fees (2.9% + 30¢): −$1,543
- Pick/pack/ship subsidy at $4.10/unit: −$4,920
- Returns at 6% with $6 handling: −$2,880
- Attributed ad spend: −$8,200
Run the same math on a $19 accessory with heavy free-shipping orders and you'll often find contribution margin below zero — a SKU that grows revenue while shrinking the bank account.
How to run this on your own store
You need order-line detail, not dashboard aggregates: export orders with SKU, price, discount, shipping charged, and region. Join against a COGS sheet. Then compute per SKU, not per store — averages are where losers hide.
Do it monthly. Ad costs and shipping rates drift; a SKU that contributed 25% in Q1 can quietly go negative by Q3 after a carrier rate hike.
ProfitFalcon runs this exact math on your store exports — every number verifiable.
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