⚡ THE ESSENTIALS IN 20 SECONDS
- Contribution margin is what you keep from each sale after paying variable costs.
- On a marketplace it includes product cost, fees, shipping or fulfillment and other per-sale charges.
- It is the ceiling on what you can spend on ads per sale without losing money.
- If you do not know it, any target ACOS is a guess.
IN THIS ARTICLE
When a client tells me “I want a 20% ACOS”, my first question is: what is your contribution margin? Often nobody knows it precisely. Without that number, there is no way to tell whether a campaign makes or loses money.
Contribution margin: the difference between the selling price and all variable costs of that sale (product, fees, shipping, packaging, payments), in money or as a percentage of price.
How to calculate it
The formula is simple: contribution margin = selling price − variable costs. To see it as a percentage, divide the result by the price.
| Item | Fictional example (USD) |
|---|---|
| Selling price | 30.00 |
| Product cost | 10.80 |
| Marketplace fee | 4.50 |
| Fulfillment | 3.60 |
| Packaging and other variables | 0.90 |
| Contribution margin | 10.20 (34%) |
In this example, every sale leaves 10.20 dollars to cover advertising, fixed costs and profit.
Why it decides your ACOS
If your contribution margin is 34%, a 34% ACOS means advertising eats the entire profit of that sale: it is your break-even point. That is why target ACOS should sit below margin, unless you are deliberately investing in a launch or in rank.
Common calculation mistakes
- Forgetting fees or fulfillment charges that change by size or category.
- Using list price instead of the real average price (with promotions).
- Ignoring returns in categories where they are frequent.
- Calculating it once and never updating it when costs or prices change.
How to use it in your strategy
- Calculate margin per SKU, not per brand.
- Set a target ACOS per SKU: lower for thin-margin products, higher for wide-margin ones.
- Separate launch products (temporarily higher ACOS) from mature products (profit ACOS).
- Watch TACOS to see the effect on total business. Pacing matters too: Amazon Ads pacing.
Contribution margin by channel: Amazon, Walmart and DTC
The same product can have very different margins depending on where you sell it. Each marketplace charges different fees, fulfillment changes (marketplace fulfillment or your own shipping) and the average price is not always the same because of promotions. That is why I recommend calculating margin per SKU and per channel.
| Channel (fictional) | Price | Variable costs | Margin |
|---|---|---|---|
| Marketplace A | USD 30 | USD 19.80 | 34% |
| Marketplace B | USD 29 | USD 20.90 | 28% |
| Own store | USD 31 | USD 17.40 | 44% |
With this table the conversation changes: each channel’s target ACOS must differ, because the margin that funds it differs too.
A real-life style decision (fictional)
A personal care brand had a 30% ACOS on its hero product and wanted to cut it to 15% “because it was too high”. Calculating contribution margin per SKU showed that product had a 48% margin: at 30% ACOS it still earned 18 points per sale and was growing organic sales. The real problem was another SKU with a 22% margin and 28% ACOS, losing money on every paid sale. Moving budget from the second to the first made the account more profitable without spending an extra dollar.
There is no “high” or “low” ACOS in the abstract: there is only ACOS above or below your contribution margin.
Checklist before setting your target ACOS
- Contribution margin calculated per SKU and per channel.
- Average real selling price, including promotions.
- Returns rate included for categories where it matters.
- Launch versus mature products separated.
- Quarterly review date on the calendar.
Agency secrets about margins
What I learned on large accounts:
Without margin per SKU I cannot design a strategy. It is the first thing I request at onboarding.
A 50% margin product can take more investment than a 20% one. One ACOS for the whole account leaves money on the table.
Inflation, exchange rates or new fees change margin. Review it every quarter.
The best conversations with finance start with contribution margin. When you speak their language, the ad budget stops looking like a cost and starts looking like an investment.
I’m Alonso Jiménez, a Retail Media account director. I manage campaigns on Amazon, Walmart, Target, Instacart and Mercado Libre every day, for brands in the US, Mexico and Latin America. Want to review your margins and target ACOS together? See my services.
Frequently asked questions
What is contribution margin?
What you keep from each sale after variable costs: product, fees, fulfillment and other per-sale charges.
How is it different from gross margin?
Gross margin usually subtracts only product cost; contribution margin subtracts all variable costs of the sale.
How does it relate to ACOS?
Your contribution margin is your break-even ACOS: if ACOS equals it, advertising takes the whole profit of that sale.
How often should I update it?
Every quarter or whenever costs, prices or marketplace fees change.