Advertising
What is Break-even ACoS?
The advertising cost of sales at which an extra advertised order adds nothing and costs nothing, because the ad spend exactly eats the margin on that sale. It is your ceiling, and it comes from your own margin rather than from any industry benchmark.
Why it matters in practice
Break-even ACoS is simply your contribution margin expressed as a percentage of the selling price, so a product that keeps a quarter of its price after product cost, fees and shipping breaks even at an ACoS of a quarter. It matters because it turns an abstract efficiency number into a decision rule: above it you are buying sales at a loss, below it every advertised order contributes. In practice it is not one number for the account but one per product, which is why an account-level ACoS target quietly overspends on thin-margin items and starves the ones that could take more. Worked in words: two products at the same ACoS can be a win and a loss at the same time, because the ceiling is set by the margin of each, not by the average of both.
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