How break-even ACoS is calculated
Break-even ACoS is the advertising cost of sale at which a campaign makes you exactly nothing. Spend less and the product is profitable; spend more and every additional sale costs you money. It is one of the few Amazon metrics with a clean definition:
Break-even ACoS = Net profit before ads ÷ Selling price × 100
Which means break-even ACoS is simply your net margin before advertising. A product with a 32% margin before ads has a 32% break-even ACoS. There is no separate formula to memorise — if you know your margin, you know your ceiling.
A worked example
A product selling at $29.99 in a 15% referral category:
So you can spend up to $11.14 to win a sale before the sale stops being worth having. If you want to keep a 15% margin rather than break even, the target ACoS drops to roughly 22% — the calculator above works this out for any profit goal you set.
Break-even ACoS, target ACoS and TACoS
Break-even ACoS is your ceiling — the point of zero profit. Useful as a limit, not as a goal.
Target ACoS is the number you actually manage to, set by the margin you want to keep. It is always below break-even, and the gap between them is your profit.
TACoS (total advertising cost of sale) measures ad spend against total revenue, organic sales included. ACoS tells you whether a campaign is efficient; TACoS tells you whether advertising is building the business or propping it up. A falling TACoS with flat ad spend means organic rank is doing more of the work — which is usually the actual goal. We wrote about the distinction in TACoS vs ACoS.
When running above break-even is the right call
Break-even ACoS is a ceiling for a mature product, not a rule for every situation. Three cases where deliberately exceeding it makes sense:
- Launching. Early sales velocity drives organic rank. Many sellers run at 100%+ ACoS for the first few weeks, treating the loss as a launch cost rather than a margin failure — but with a fixed budget and an end date.
- Products with genuine repeat purchase. If a meaningful share of buyers come back, the first sale can lose money because lifetime value exceeds it. This justifies far less overspend than most sellers assume — check your actual repeat rate before relying on it.
- Clearing aged inventory. If units are approaching an aged inventory surcharge band — the surcharge starts at 181 days and steps up sharply at 271 — selling at a thin loss can beat paying storage penalties on stock that is not moving.
What sellers most often get wrong
- Calculating break-even on gross margin. If your margin figure does not already subtract the referral fee, the FBA fee and landed cost, your break-even ACoS is fiction — and always too generous.
- Forgetting returns. ACoS is measured against gross sales. A 10% return rate means your effective break-even is roughly 10% lower than the calculator shows.
- Using one ACoS target across every SKU. Break-even ACoS is a property of a product's margin, not of your account. A 45%-margin product and a 20%-margin product cannot share a target.
- Ignoring price changes. Drop your price to win the Buy Box and your break-even ACoS falls at the same time — the moment you can least afford the same ad spend.
This calculator works at the product level using the numbers you type in. To see actual ACoS and true margin per SKU across every order — with ad spend reconciled against real FIFO cost of goods — SellerGuards pulls it directly from Amazon's SP-API.