The Complete Guide to E-commerce Profitability

Profit isn't one number. Revenue is the top line. Subtract cost of goods (COGS) and you have gross profit. Subtract the rest of the variable costs — shipping, payment and marketplace fees, discounts, returns and ads — and you have contribution profit. Subtract fixed costs (rent, salaries, software) and you have net profit, the real bottom line.

Each rung answers a different question. Gross margin tells you if a product is fundamentally viable. Contribution margin tells you if selling more actually helps. Net profit tells you if the business makes money. Confusing them is the most common — and most expensive — profit mistake.

The number that flatters you most is the one that leaves costs out. At minimum include: product cost, inbound freight, packaging, payment processing fees, marketplace or platform fees, shipping to the customer, discounts, a returns allowance, and advertising. These are variable — they rise with each order — so they sit above contribution profit.

Fixed costs (rent, salaries, software subscriptions) don't scale per order, so they belong below contribution, at the net-profit step. Keeping the two straight is what makes contribution margin such a useful decision tool.

Period totals hide problems. A store can be net-profitable overall while half its SKUs lose money on every sale. Divide contribution profit by orders to get profit per order, then look at it per product — you'll usually find a few “bestsellers” that contribute almost nothing once fees and returns are counted.

Profit per order also sets your acquisition ceiling: it's essentially your break-even CPA — the most you can pay to win an order before it stops making money.

These three quietly reshape profitability. A discount comes straight off contribution — a 20% promo on a 40%-margin product roughly halves your profit per order. Free shipping is a real per-order cost that has to be earned back through higher AOV or margin. And returns cost you twice: the refund and the return shipping and processing.

Model them before you run them. The question is never “did the promo drive sales?” — it's “did the promo make money after the discount, the shipping and the returns?”

This is the classic trap. Work down the ladder: is COGS creeping (supplier price, freight)? Are fees a bigger share (channel mix shifting to higher-fee marketplaces)? Are discounts deeper or more frequent? Is ad spend rising faster than sales (a falling blended ROAS / MER)? Are returns climbing?

Usually it's ads or discounts — they move fastest and hurt most. Check your MER and your discount rate first.

The same item earns different profit on each channel because the fee structures differ. Amazon takes a referral fee (~15%) plus FBA fulfilment and storage; Shopify takes platform and payment fees but you carry fulfilment and acquisition. Compare profit per order by channel, not revenue — the channel that looks biggest isn't always the one that pays best.