Break-even ACOS: how much you can spend on Amazon advertising
Updated 9 October 2026 · Pablo Pedrajas
ACOS is what you spend on advertising divided by the sales that advertising generates, as a percentage. Break-even ACOS is the point where advertising eats exactly your margin: it equals your margin before advertising divided by the sale price. Below that ACOS, every ad-driven sale leaves you money; above it, you lose money. It's calculated per product and per country, using the same VAT treatment as your advertising report.
What ACOS is
Amazon Ads defines it like this:
ACOS = advertising spend ÷ sales attributed to advertising × 100
If you spend €30 and the ads generate €150 in sales, your ACOS is 20%. ROAS is the same figure the other way round: 150 ÷ 30 = 5.
ACOS only tells you what it costs to sell with ads. Whether that cost is good or bad depends on your margin, and Amazon doesn't know that.
How to calculate break-even ACOS
Amazon Ads itself sums it up in one sentence: to stay profitable, ACOS has to be below your margin. As a formula:
Break-even ACOS = margin before advertising ÷ sale price
Using the example from the real margin guide: margin before advertising of €8.27 and a price of €29.90 including VAT (€24.71 excluding VAT).
- If your advertising report counts sales including VAT: 8.27 ÷ 29.90 = 27.7%.
- If it counts them excluding VAT: 8.27 ÷ 24.71 = 33.5%.
The difference isn't small. Check how your report counts sales and use the same treatment in the numerator and the denominator; otherwise you get the ceiling wrong.
Your target ACOS depends on what you're after
Break-even is the limit, not necessarily your target:
- Making money on a product that already sells: ACOS below break-even, with a cushion to cover fixed costs.
- Launching a product or gaining ranking: you can accept an ACOS above break-even, losing money on each ad-driven sale, as long as it's a decision with a time limit and a budget, not something that happens without you noticing.
- Defending your brand searches: they usually have a low ACOS and are looked at separately.
What matters is that every product has a known ceiling. Without it, advertising is a bet.
ACOS and TACoS
TACoS (total ACOS) isn't an official Amazon metric, but it's widely used: it divides advertising spend by all of the product's sales, including organic ones.
- ACOS tells you whether each campaign is profitable.
- TACoS tells you how much advertising weighs on the product's whole business.
If TACoS falls over time while sales rise, advertising is helping the product also sell without ads. If it keeps rising, you depend more and more on paying for every sale.
Common mistakes
- Using a generic target ACOS ("25% is fine") without looking at that product's margin.
- Calculating break-even with the gross margin, without subtracting fulfilment, storage or returns: the ceiling comes out too high.
- Mixing VAT treatments between the advertising report and the margin calculation.
- Looking at the account average instead of each product: a good average can hide products that lose money on every click.
Frequently asked questions
How is ACOS calculated on Amazon?
By dividing advertising spend by the sales attributed to that advertising and multiplying by one hundred. If you spend €30 and sell €150 through ads, ACOS is 20%.
What is a good ACOS?
One below your break-even ACOS, which is your margin before advertising divided by the sale price. There's no universal good ACOS: it depends on each product's margin.
What is the difference between ACOS and TACoS?
ACOS divides advertising spend by the sales that come from ads. TACoS divides it by all of the product's sales, including organic ones.
Can an ACOS higher than my margin make sense?
Yes, as a temporary decision to launch a product or gain ranking, with a defined time limit and budget. Kept up indefinitely, it means losing money on every ad-driven sale.
Sources (official documents, in Spanish)
General information based on Spanish rules in force on 9 October 2026. It is not a substitute for analysing a specific case.
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