If you run Amazon ads for a book, ACOS is the number the console puts in front of you most often. It is also the one that is easiest to misread. A 40% ACOS can be a healthy profit on one book and a steady loss on another. This guide explains what ACOS measures, how to calculate it, and how to decide what a good ACOS is for your own titles.
What ACOS means
ACOS stands for advertising cost of sales. It tells you how much you spent on ads for every dollar of sales those ads brought in, written as a percentage. Amazon calculates it for every campaign, ad group, keyword and search term, for whatever date range you pick.
Lower means the ads are cheaper relative to the sales they produce. Higher means you are paying more to make each sale. On its own, though, the number says nothing about profit. For that, you need to compare it with what you actually earn from a sale, which is where break-even ACOS comes in.
ACOS = ad spend ÷ ad sales × 100
Both numbers come from the same period and the same campaign, keyword or search term. "Ad sales" is what buyers paid for the book, not your royalty.
A worked example
Say a campaign spent $30 last month and Amazon attributes $100 of book sales to it. Divide the spend by the sales and multiply by 100:
| Ad spend | Ad sales | Sum | ACOS |
|---|---|---|---|
| $30.00 | $100.00 | 30 ÷ 100 × 100 | 30% |
| $45.00 | $60.00 | 45 ÷ 60 × 100 | 75% |
| $12.00 | $0.00 | no sales | — |
The last row matters as much as the first. When a keyword spends money and sells nothing, there is no ACOS to show, and the console often displays a dash. That spend is still real, and it is usually the first thing worth cutting.
ACOS, TACOS and ROAS
Two related numbers turn up next to ACOS. They use the same inputs, arranged differently:
| Metric | Formula | $30 spend, $100 ad sales, $250 total sales | Read it as |
|---|---|---|---|
| ACOS | spend ÷ ad sales | 30% | Cost of the sales the ads made |
| TACOS | spend ÷ total sales | 12% | Ad cost against every sale of the book, organic included |
| ROAS | ad sales ÷ spend | 3.33 | Sales per $1 of ads; the inverse of ACOS |
ACOS is the one to act on keyword by keyword. TACOS is useful for seeing whether advertising is lifting a book's overall sales or just buying the same sales you would have made anyway.
Break-even ACOS: the number that decides profit
Your break-even ACOS is the highest ACOS at which an ad sale still pays for itself. It equals your royalty per copy divided by the list price, as a percentage. Below it, the ads make money on each sale. Above it, every ad sale costs more than it earns.
royalty per copy ÷ list price × 100
An eBook example
A $9.99 eBook on the 70% royalty option earns roughly $6.99 a copy, so its break-even ACOS is about 70%. The real figure is a little lower, because KDP deducts a delivery cost based on file size from 70% royalties. Use the royalty KDP shows you for your book rather than the headline rate.
A paperback example
Paperback royalties are usually worked out as the list price times 60%, minus the printing cost. A $12.99 paperback with a $3.50 printing cost earns about $7.79 − $3.50 = $4.29, so its break-even ACOS is 4.29 ÷ 12.99 ≈ 33%. The same ACOS of 40% that is comfortably profitable on the eBook loses money on this paperback.
Rates and printing costs differ by format, marketplace and page count, so check the rate KDP shows you for each book before you set a target.
Free toolBreak-even ACOS for KDPPick the format and royalty, enter your price, get the line your ACOS should stay under.What a good ACOS is for a book
There is no single good ACOS. A good ACOS is one comfortably below your break-even for that book. For a 70% eBook that might leave plenty of room; for a low-priced paperback the room is much smaller.
Series change the picture. If the first book leads readers on to the rest, an ad sale is worth more than its own royalty. Some authors deliberately run the first book above break-even because read-through makes the money back. That is a reasonable choice when you know your read-through, and a costly one when you are guessing. Kindle Unlimited page reads are reported separately from ad sales, so a KU book's ACOS on its own can understate what its ads earn.
- Below break-even: each ad sale is profitable. Consider raising bids on what sells.
- Around break-even: the ads roughly pay for themselves. Watch the trend.
- Above break-even: every ad sale loses money unless read-through makes it back.
Seeing ACOS across every period
A single ACOS for a single date range hides a lot. A keyword can look expensive over 30 days and excellent over its lifetime, or the other way round. Seasonal books look terrible in summer and perfect in December.
AcosControl puts up to ten periods side by side on every campaign and keyword, so today, the last 30 days, the same month last year, last Christmas and lifetime sit on one row. The pattern is visible before you change a bid. Try the live demo to see how it looks.
Common questions
What does ACOS stand for?
ACOS stands for advertising cost of sales (sometimes written ACoS). It is the share of your ad-attributed sales that you spent on the ads that produced them.
What is the ACOS formula?
ACOS = ad spend ÷ ad sales × 100. Spend $30 to make $100 in ad sales and your ACOS is 30%.
What is a good ACOS on Amazon for a book?
One comfortably below your break-even ACOS, which is your royalty per sale divided by your list price. There is no single good number: a 70% eBook has far more room than a low-priced paperback.
Is a lower ACOS always better?
Not always. A very low ACOS can mean bids are so cautious that you are missing sales you could have made profitably. The goal is the most profit, which usually sits between a very low ACOS and your break-even.
- ACOS = ad spend ÷ ad sales × 100, for the same period.
- Break-even ACOS = royalty per copy ÷ list price × 100. Use the royalty KDP shows you.
- A good ACOS sits comfortably below break-even for that book.
- Spend with no sales has no ACOS, and it is often the first thing to cut.
- Read-through and page reads can justify a higher ACOS on the first book in a series.