SOLUTIONS
Revenue is growing but margins are shrinking: where ecommerce margin goes
Fees, ads and returns grow quietly, SKU by SKU, until growth stops paying for itself. Find the SKUs, fix them and keep watching.
Profit Leak Scan free · Margin Guard $1,500 to $3,500 · Pulse in every Ops Desk plan
When ecommerce revenue is growing but margins are shrinking, the cause is almost never one big cost. Fees, ad spend, discounts, returns and storage rise SKU by SKU while everyone watches the top line. Find them by calculating contribution margin for every SKU on every channel after every cost, set a floor and fix the SKUs below it.
What it looks like
"Revenue is up, but margin is not."
Sales are up 30% on last year and the bank balance has not moved. Nobody can say which SKUs lose money after fees. Ad budgets are set from a revenue target. The Amazon payout never matches what the spreadsheet says the month should have made, and nobody has time to find out why.
It is a common way for a growing brand to stall, and it is fixable once you can see margin by SKU instead of revenue by month.
What it costs when revenue is growing but margins are shrinking
Marketplace fees alone can take half of every sale. Marketplace Pulse, an independent analyst, found that Amazon's referral fee, FBA fees and advertising together took more than 50% of revenue for the sellers whose P&Ls it reviewed, up from 40% five years earlier (Marketplace Pulse, Feb 13, 2023). Its breakdown: about 15% referral, 20% to 35% for FBA including storage and up to 15% for advertising and promotions.
The fees keep moving, and each change lands on every unit you sell:
| Change | Date | Source |
|---|---|---|
| Amazon FBA fulfillment fees up an average $0.08 a unit | From Jan 15, 2026 | Amazon, via Supply Chain Dive (Oct 17, 2025) |
| Amazon 3.5% fuel and logistics surcharge on FBA fulfillment fees, called temporary by Amazon and in place until further notice | From Apr 17, 2026 (May 2, 2026 for Multi-Channel Fulfillment) | Digital Commerce 360 (Apr 3, 2026) |
| Amazon holiday peak fulfillment fee averaging $0.32 a unit, with the surcharge on top | Oct 15, 2026 to Jan 14, 2027 | Retail Dive (Jul 14, 2026) |
| Walmart referral fee set by contract category: 15% for Everything Else, each category its own rate | Schedule dated Mar 9, 2026 | Walmart referral fee schedule |
| Shopify Basic online card rate 2.9% + 30¢ on standard cards; premium cards 3.5% + 30¢ | Viewed Oct 20, 2026 | Shopify pricing |
| Walmart WFS long-term storage: $2.25 per cubic foot a month for days 366 to 450, $7.50 after 450 | From Jun 30, 2026 | Walmart WFS fees (May 27, 2026) |
Our Amazon FBA fees 2026 guide tracks every change as it lands.
Price yours: for each SKU, units sold a year × the gap between its contribution margin per unit and your target. Add the SKUs together and you have the size of the problem.
Three levels of margin
Contribution margin answers a different question at each level, so calculate all three.
| Level | Revenue minus | Tells you |
|---|---|---|
| Contribution margin 1 | Product cost and landed cost (freight, duty, inbound) | Whether the product works at this price |
| Contribution margin 2 | Plus referral and payment fees, fulfillment, storage and returns | Whether the channel works |
| Contribution margin 3 | Plus ad spend | Whether growth pays for itself |
The per-unit formula and a worked example are on our profit and cash reporting page.
Seven places margin goes as revenue grows
Each of these hides inside a growing top line. Each has a check you can run.
- 01Ad spend set by a revenue target.
Check ad cost per unit by SKU, not ACoS across the account.
- 02Slow SKUs carrying storage and aged-stock charges.
Check storage cost per unit sold, by SKU.
- 03Fee changes never priced in.
Check each price against this year's fees, not last year's.
- 04Promotions and discount codes stacking.
Check how many orders sold below your floor last month.
- 05Returns on new SKUs or new channels.
Check return rate by SKU and channel.
- 06Landed cost rising with freight or duty while prices stay put.
Check the latest supplier and freight invoices against your cost file.
- 07Payout timing hiding the trend.
Check margin by month of sale, not by payout.
The ranking changes once you sort by margin dollars instead of revenue:
| SKU | Revenue a year | Contribution margin 3 | Margin dollars | Rank by revenue | Rank by margin |
|---|---|---|---|---|---|
| A | $420,000 | 12% | $50,400 | 1 | 1 |
| B | $310,000 | 4% | $12,400 | 2 | 4 |
| C | $180,000 | 22% | $39,600 | 3 | 2 |
| D | $95,000 | 26% | $24,700 | 4 | 3 |
Illustrative · sample figures
SKU B is the second-largest seller and the weakest earner. Where ad budgets follow revenue, it may also be the SKU getting the most spend.
How to fix shrinking margins, step by step
- 01Calculate contribution margin per SKU and channel, after every cost.
All three levels.
- 02Rank SKUs by margin dollars, not revenue.
- 03Set a floor per SKU.
The lowest contribution margin you accept, written down.
- 04Fix every SKU below its floor.
Raise price within your band, cap ad cost per unit, bundle, change fulfillment, renegotiate cost or discontinue. One change at a time, so you can see what worked.
- 05Re-cost on every fee or landed cost change.
Fee announcements are dated; put them in the calendar.
- 06Review monthly.
Same report, same day.
What to do yourself first
- Export the last 90 days of orders by SKU and channel.
- Build one sheet with columns for price, referral fee, fulfillment, storage, payment fee, returns, ads, shipping and landed cost.
- Find the 10 top-selling SKUs with the lowest margin.
- Compare each one's ad cost per unit with its margin per unit.
- List every fee line on your Amazon, Walmart and Shopify statements you cannot explain.
The fee and margin calculator does the per-unit arithmetic for a single product.
How we run it
The free Profit Leak Scan reports margin by SKU and channel after every fee, plus a fix list ranked by dollar impact and effort, within 48 hours of working read-only access. No sales call is required, and you keep the report.
To keep it fixed, Margin Guard watches floors daily and flags any SKU that slips below one ($1,500 to $3,500, fixed in writing, included from Ops Desk Growth at $2,499 a month). Profit and Cash Pulse gives you margin and cash in one view and is included in every Ops Desk plan. If freight and duty are the moving part, Landed Cost Desk keeps your cost file current.
Founding offer: 20% off launch fees, add-ons and the Foundation, plus 20% off monthly plans for the first 6 months, for our first 25 clients or until Jan 31, 2027, whichever comes first. See pricing.
How to measure it
Contribution margin by SKU per month, with the period stated. The share of revenue coming from SKUs below their floor. Avoidable fees as a share of revenue, monthly. We report these numbers; we do not promise a margin result, because prices, fees and demand move. If margin is one of several problems at once, our common ecommerce operations problems page shows which to fix first.
What does it cost to find the margin leak?
The Profit Leak Scan is free for brands selling $1M or more a year, with a written report within 48 hours of working read-only access. Margin Guard, which watches floors daily, is $1,500 to $3,500 to build. Profit and Cash Pulse is included in every Ops Desk plan.
What is contribution margin?
What a SKU keeps after every variable cost of selling it: product and landed cost, referral and payment fees, fulfillment, storage, returns, shipping and ad spend. Calculate it per unit and per channel. It is the number that tells you whether selling more of something makes you better off.
Why does our Amazon payout not match our profit?
Payouts follow Amazon's settlement schedule, not your month. Revenue from one period and fees, refunds and reserves from another land in the same deposit. A payout is a cash event, not a month's profit. Measure margin by month of sale and reconcile payouts separately.
Should we cut ad spend?
Not across the board. Cap ad cost per unit by SKU instead, set from that SKU's margin. Some SKUs can carry more spend than they get today; others lose money on every advertised sale. A flat cut punishes both the same way.
Which Amazon fees changed in 2026?
FBA fulfillment fees rose an average $0.08 a unit from Jan 15, 2026. A 3.5% fuel and logistics surcharge on fulfillment fees started on Apr 17, 2026. The holiday peak fee averages $0.32 a unit from Oct 15, 2026 to Jan 14, 2027, with the surcharge on top.
How often should we review margin?
Monthly by SKU and channel, and every time a fee or landed cost changes. Fee changes are announced with dates, so re-cost before they start, not after the first statement. A monthly review on a fixed day catches drift before it becomes a quarter of lost margin.
Growth only pays when you watch margin by SKU, not revenue by month.
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Sources7 sources
- 01marketplacepulse.comMarketplace Pulse, Feb 13, 2023; checked Oct 20, 2026Primary
- 02supplychaindive.comSupply Chain Dive, FBA fee change from Jan 15, 2026, Oct 17, 2025; checked Oct 20, 2026Primary
- 03digitalcommerce360.comDigital Commerce 360, 3.5% surcharge, Apr 3, 2026; checked Oct 20, 2026Primary
- 04retaildive.comRetail Dive, 2026 holiday peak fee, Jul 14, 2026; checked Oct 20, 2026Primary
- 05sell.amazon.comAmazon referral fees vary by category; checked Oct 20, 2026Primary
- 06shopify.comShopify card rates; checked Oct 20, 2026Primary
- 07marketplacelearn.walmart.comWFS storage fees, last updated May 27, 2026; checked Oct 20, 2026Primary
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