What Is ACoS (Advertising Cost of Sales)?
ACoS (advertising cost of sales) is the share of ad-attributed sales spent on advertising, calculated as ad spend divided by ad sales times 100; an ACoS of 25% means $25 of ad spend for every $100 in ad sales.
Formula: ACoS = ad spend ÷ attributed ad sales × 100.
Example: a campaign spends $300 and drives $1,200 in attributed sales. ACoS = 300 ÷ 1,200 × 100 = 25%.
How to judge it
An ACoS is good or bad only against your margin. Your break-even ACoS equals the margin before ad spend: below it an ad sale earns profit, above it the sale loses money. Launch campaigns and brand defense often run above break-even on purpose, while campaigns for mature products usually aim below it.
ACoS counts only sales Amazon attributes to the ad within the attribution window. It misses the organic sales ads help create, so brands track TACoS beside it. ROAS is the same ratio turned upside down.
Common mistake
Pushing ACoS down at any cost. Cutting bids on everything that is not cheap lowers ACoS and usually lowers total sales and organic rank with it. Our full ACoS guide covers benchmarks, break-even math and the levers that change ACoS.