Most Shopify sellers track COGS and think they know their margins. They don't. There are at least 10 costs that eat into your profit on every order, and almost none of them show up in Shopify's built-in reports. The result: you think you're making 60% margin when the real number is closer to 8%.
Here is the full list. Treat it as a checklist. If you are not tracking every line below at the SKU level, your margin numbers are wrong.
The margin leak checklist
These are the 10 variable and semi-variable costs that reduce your per-order profit. Shopify tracks exactly one of them (shipping, partially). The rest are invisible unless you build your own tracking or use a dedicated margin tool.
| # | Cost | Typical Range | Shopify Tracks It? |
|---|---|---|---|
| 1 | Payment processing fees | 2.6–2.9% + $0.30/order | No |
| 2 | Shipping & carrier costs | $3–$12 per order | Partially |
| 3 | Return shipping costs | $5–$10 per return | No |
| 4 | Return processing labor | $2–$5 per return | No |
| 5 | Packaging materials | $0.50–$3 per order | No |
| 6 | Fulfillment labor or 3PL fees | $2–$5 per order | No |
| 7 | Customer acquisition cost (CAC) | $15–$50+ per customer | No |
| 8 | Shopify subscription + app costs | $39–$399/mo + apps | No |
| 9 | Chargebacks & fraud losses | $0.50–$1 per order avg | No |
| 10 | Inventory shrinkage & damage | 1–3% of inventory value | No |
Some of these are per-order costs (payment fees, packaging). Others are allocated costs that you spread across units sold (CAC, Shopify subscription). Either way, they reduce the cash you actually keep from each sale.
The danger is not any single cost. It is the accumulation. Each line looks small in isolation — 2.9% here, $1.25 there. But they compound. Let's see what that looks like on a real product.
How these stack up: the death-by-a-thousand-cuts effect
Take a product you sell for $35 with a $14 landed cost. Shopify says you have a 60% gross margin — $21 of profit per unit. That sounds healthy. Now load in every hidden cost:
| Line Item | Amount | What's Left |
|---|---|---|
| Sale price | $35.00 | $35.00 |
| COGS (40%) | ($14.00) | $21.00 |
| Payment processing (2.9% + $0.30) | ($1.32) | $19.68 |
| Shipping (free shipping absorbed) | ($5.50) | $14.18 |
| Return allowance (15% rate) | ($1.50) | $12.68 |
| Packaging materials | ($1.25) | $11.43 |
| Fulfillment / 3PL fees | ($3.00) | $8.43 |
| CAC (blended) | ($4.50) | $3.93 |
| Chargebacks & fraud | ($0.40) | $3.53 |
| Shopify + apps (allocated) | ($0.60) | $2.93 |
Your $21 of "profit" turned into $2.93. Eight separate costs ate $18.07 between your gross margin and your true contribution. Not one of those costs exceeded $5.50 individually. That is the death-by-a-thousand-cuts problem: each leak is small enough to ignore, but together they consume 86% of your gross profit.
At $2.93 per unit, a $1 increase in shipping rates drops your margin to $1.93. A 20% jump in ad costs wipes out another $0.90. The product that looked like a 60% margin winner is actually one cost increase away from breaking even.
Which leaks matter most for you
Not every cost hits every store equally. The biggest margin leak depends on what you sell, how you sell it, and how you acquire customers. Here is a quick guide to where to look first:
| Store Type | Biggest Leak | First Move |
|---|---|---|
| Apparel & fashion | Returns (15–30% rate) | Track return cost per SKU, reduce with fit guides |
| Heavy / bulky goods | Shipping ($8–$15/order) | Negotiate dimensional weight rates, regional 3PLs |
| DTC brands (ad-driven) | CAC ($20–$50+) | Allocate ad spend per SKU, pause ads on low-margin items |
| Subscription / consumables | Churn & reacquisition | Measure net CAC (acquisition minus retained LTV) |
| Low-AOV / accessories | Payment fees (4–5% on <$15) | Bundle to raise AOV, offset fixed $0.30 fee |
The pattern: the cost you are least likely to track per SKU is usually the one doing the most damage. CAC is the classic example. Most sellers know their blended CAC, but almost nobody allocates it to individual products. That means high-CAC SKUs hide behind low-CAC ones, and your averages mask the problem.
How to track this per SKU
Knowing the checklist exists is step one. The real leverage comes from tracking these costs per product, not as store-wide averages.
Store-wide averages hide your worst offenders. A 10% blended margin might mean five SKUs at 20% and five SKUs at 0%. The profitable products subsidize the money-losing ones, and you never see it because the average looks acceptable.
Per-SKU tracking exposes the spread. It shows you which products are actually profitable after all costs and which ones are bleeding cash. Without that granularity, you are making pricing and ad-spend decisions based on incomplete data.
The manual approach: export your SKUs from Shopify, build a spreadsheet with columns for each of the 10 costs above, and calculate true contribution per product. It works, but it breaks every time your costs change — and costs change constantly.
MarginCaptain's interactive demo shows what per-SKU margin analysis looks like when every cost is loaded in. You can see exactly how a 10-product catalog breaks down from gross margin to true contribution — and which SKUs are hiding losses behind healthy-looking averages.
Stop using gross margin as your scoreboard
Shopify gross margin is not wrong. It is incomplete. It answers the question "what does this product cost to make?" but ignores the question "what does this product cost to sell and deliver?" Those are different questions, and the gap between them is where margin leaks live.
Run through the checklist above for your top 5 SKUs by revenue. Add up every cost. Compare the result to what Shopify shows you. If the gap is more than 20 percentage points — and for most stores it will be — you have margin leaks worth fixing.
The stores that grow profitably are not the ones with the highest gross margins. They are the ones that know their true margins and make decisions accordingly. That starts with tracking every cost on this list, for every product, every month.