What Is ACoS? Advertising Cost of Sale Explained
DEFINITION
Advertising cost of sale is advertising spend divided by the revenue that advertising produced, expressed as a percentage. An ACoS of 25% means you spent 25p in advertising for every pound of advertising-attributed sales.
ACoS is the headline advertising metric on Amazon, and the one sellers most often chase in the wrong direction. A low ACoS is easy to achieve by spending almost nothing, and the sellers with the lowest ACoS figures are frequently the ones growing slowest.
ACoS only becomes actionable once you know the level your own margin can carry.
- The formula
How ACoS is calculated
The inverse of ROAS, expressed as a cost rather than a return.
FORMULA
ACoS = ( Ad spend ÷ Ad revenue ) × 100
Ad spend
What you paid the platform over the period. Amazon reports this directly in the advertising console, so unlike ROAS there is little ambiguity about the numerator.
Ad revenue
Sales attributed to those ads within the attribution window, which on Amazon is typically seven or fourteen days depending on the campaign type.
The relationship to ROAS
ACoS and ROAS are reciprocals. A 25% ACoS is a ROAS of 4. A 50% ACoS is a ROAS of 2. Amazon reports ACoS; most other platforms report ROAS.
A lower ACoS is not automatically better. Spending nothing produces an undefined ACoS and no sales.
- Worked example
The same ACoS on two different products
Identical advertising performance, opposite commercial outcomes, because the margin underneath is different.
Line
Product A
Product B
Selling price
40.00
40.00
Ad-attributed sales
20,000
20,000
Ad spend
5,000
5,000
ACoS
25%
25%
Cost of goods
12.00
20.00
Amazon referral fee
6.00
6.00
FBA fulfilment fee
5.20
7.40
Contribution margin before ads
41.9%
16.5%
Break-even ACoS
41.9%
16.5%
Verdict at 25% ACoS
Profitable
Loss-making
Illustrative figures chosen so the arithmetic is visible. The fee structure is real in shape; the amounts are not a quotation of current Amazon rates, which vary by category and change.
- The number that matters
Break-even ACoS
Unlike ROAS, break-even ACoS has a pleasingly simple relationship to margin: it is your contribution margin.
FORMULA
Break-even ACoS = Contribution margin %
Why they are equal
At the point where advertising cost equals the contribution the sale generates, the two percentages are the same number. A product contributing 30% can sustain a 30% ACoS before it stops making money.
What to include in margin
Cost of goods, referral fee, fulfilment fee, storage and expected returns. Leave any of them out and your break-even ACoS comes out flatteringly high.
Where to aim
Below break-even for profitability, above it deliberately and temporarily when launching a product and buying sales velocity for rank.
Launch campaigns that run above break-even ACoS are a legitimate investment in rank. Campaigns that have done so for a year are a legitimate problem.
- The other number
ACoS tells you about ads. TACoS tells you about the business
Total advertising cost of sale divides ad spend by total sales, including the organic ones, which makes it the more useful trend to watch.
Advertising that builds organic rank shows up in TACoS long before it shows up in ACoS.
A product with rising ACoS and falling TACoS is usually healthy: advertising is becoming less efficient in isolation while total sales grow faster than spend, which is what happens when organic rank is building. The reverse combination is the one to worry about.
- TACoS = ad spend ÷ total sales, including organic
- Falling TACoS over months means organic is carrying more of the load
- Rising TACoS with flat sales means you are buying the same revenue for more
- Very low TACoS on a mature product can mean you are underinvesting
- Neither number means anything without the margin underneath
Watch ACoS at campaign level for optimisation decisions, and TACoS at product level for strategic ones.
- Reading it properly
What ACoS does and does not tell you
Four things worth holding in mind before you act on the number.
It is a cost ratio, not a verdict
- Compare it to your break-even, never to a published average
- The same ACoS is excellent on one product and fatal on another
- Category fee structures change break-even substantially
- Returns belong in the margin calculation
Launch ACoS should be high
- Sales velocity drives rank, and rank drives organic sales
- A deliberate loss during launch buys a position
- Set a time limit and a spend cap before you start
- Review at the end of it rather than drifting
Low ACoS can mean underinvestment
- The lowest ACoS usually comes from branded terms only
- Those shoppers were often going to find you anyway
- Cutting spend raises ACoS efficiency and shrinks the business
- Judge on contribution in currency, not on the ratio
It multiplies listing quality
- ACoS is conversion rate wearing a different hat
- A listing converting badly makes every campaign expensive
- Fixing images often moves ACoS further than bid changes
- Check the listing before rebuilding the campaigns
The Amazon listing checklist covers the conversion side, which is usually the cheaper half of an ACoS problem.
- Common mistakes
Three ways ACoS gets misused
Each appears regularly in accounts we take over.
Cutting spend to hit an ACoS target
It works immediately and costs you rank. Sales velocity falls, organic position slips, and three months later the same ACoS target requires even more efficient spend to reach. Target contribution instead.
Using one target across the whole catalogue
Break-even ACoS varies product by product because cost of goods and fulfilment fees vary product by product. A single account-wide target overspends on thin-margin lines and underspends on the profitable ones.
Ignoring TACoS entirely
ACoS alone cannot tell you whether advertising is building the organic base or substituting for it. A product whose ACoS is stable while TACoS climbs is quietly becoming dependent on paid traffic.
How to bring ACoS down without losing volume, using campaign architecture rather than bid cuts: read the full article.
- Related terms
Terms that travel with this one
ACoS only makes sense alongside these.
TACoS
Total advertising cost of sale: ad spend divided by total sales including organic. The better strategic trend.
Sales velocity
How fast a product sells over a period. A major marketplace ranking input, and what launch advertising is buying.
Buy box
The purchase panel on a listing. Advertising to a listing you do not hold the buy box on sends your budget to another seller.
Contribution margin
What remains after goods, fees and fulfilment. Your break-even ACoS is this number.
Revenue per order. Raising it lowers ACoS at constant spend without touching a single bid.
- Questions
ACoS FAQs
What sellers ask most often about the number.
What is a good ACoS?
Anything comfortably below your break-even ACoS, which equals your contribution margin on that product. A 30% ACoS is healthy on a product contributing 45% and loss-making on one contributing 20%. Published averages are not a useful target because they average across categories with very different fee structures.
How do I calculate break-even ACoS?
Work out contribution per unit: selling price minus cost of goods, referral fee, fulfilment fee, storage and expected returns. Divide that by the selling price. The resulting percentage is both your contribution margin and your break-even ACoS.
What is the difference between ACoS and TACoS?
ACoS divides ad spend by advertising-attributed sales only. TACoS divides the same spend by total sales including organic. ACoS tells you how the campaigns are performing; TACoS tells you whether advertising is building the business or propping it up.
How is ACoS different from ROAS?
They are the same relationship inverted. ROAS is revenue divided by spend, expressed as a multiple; ACoS is spend divided by revenue, expressed as a percentage. Amazon reports ACoS, and most other advertising platforms report ROAS.
Should ACoS be high when launching a product?
Usually yes, deliberately. Early sales velocity drives organic rank, and rank drives the sales that eventually make the product profitable without advertising. Set a budget cap and an end date before you start, so the launch phase ends rather than becomes the permanent state.
My ACoS is rising. What should I check first?
The listing, before the campaigns. ACoS is conversion rate in disguise, so a change in images, price, reviews or buy box ownership moves it faster than any bid adjustment. Then check for new competitors on your main terms.
Does a lower ACoS always mean more profit?
No. The easiest way to lower ACoS is to spend only on branded and highly specific terms, which reaches people already looking for you. Efficiency improves, volume falls, and contribution in currency — the number the business actually banks — usually falls with it.
Can you work out our break-even ACoS per product?
Yes. It is included in the marketplace section of the free eCommerce audit, and it is usually the calculation that changes how a seller sets budgets.
- Keep reading
Related resources
Where to go once you know your break-even figure.
INSIGHT
How to bring advertising cost down on a mature account without giving up the volume it is buying.
CHECKLIST
Thirty-eight checks to run before advertising, because listing quality multiplies everything you spend.
DEFINITION
The same relationship expressed as a return rather than a cost, and how to calculate break-even ROAS.
Chasing an ACoS target nobody calculated?
A free eCommerce audit works out break-even ACoS per product from your real cost of goods and fees, then tells you which campaigns are above it and why.