ACOS calculator for books
Find your break-even ACOS and see whether your Amazon ads make or lose money on every sale.
ProfitableYour ACOS of 26.7% is 2.6 points under your 29.3% break-even.
- ACOS
- 26.7%
- ROAS
- 3.75
- Break-even ACOS
- 29.3%
- Royalty per sale
- $4.39
- Ad cost per sale
- $4.00
- Profit per sale
- $0.39
- KU pages (estimate)
- Read-through (estimate)
- Profit from sales only
- True break-even ACOS
Where the list price of one ad sale goes
| ACOS | Ad spend | Per sale | Total |
|---|---|---|---|
| 10.0% | $37.48 | $2.89 | $72.27 |
| 20.0% | $74.95 | $1.39 | $34.80 |
| 26.7%Yours | $100.00 | $0.39 | $9.75 |
| 29.3%Break-even | $109.75 | $0.00 | $0.00 |
| 30.0% | $112.43 | -$0.11 | -$2.68 |
| 40.0% | $149.90 | -$1.61 | -$40.15 |
| 50.0% | $187.38 | -$3.11 | -$77.63 |
| 60.0% | $224.85 | -$4.60 | -$115.10 |
| 70.0% | $262.33 | -$6.10 | -$152.58 |
Rather have a pro handle this? Our studio can: book marketing.
Short answer
ACOS is ad spend divided by ad sales. Your break-even ACOS is your royalty divided by the list price: a $14.99 paperback that earns $4.39 breaks even at 29.3%. Below that, each ad sale makes money. Above it, you lose money unless Kindle Unlimited pages or later books in the series make up the difference.
How to use it
- Choose Paperback or Kindle ebook, then the store, list price and the details that set your royalty.
- Copy ad spend and ad sales from your Amazon Ads report, or enter orders instead of sales.
- Read the verdict: your ACOS against your break-even ACOS, and the profit or loss.
- For a KU book or a series, switch to Add KU and series and enter your own pages read and read-through.
- Check the table for the profit at other ACOS values, then copy the result or the share link.
How it works
ACOS = ad spend / ad sales x 100
ROAS = ad sales / ad spend
Break-even ACOS = royalty per sale / list price
Profit = ad sales / list price x royalty - ad spend
ACOS and ROAS follow Amazon Ads' own definitions. The royalty per sale comes from the same KDP rules as our royalty calculator: the paperback rate times the list price minus printing, or the ebook rate times the price minus delivery and VAT. Ad sales are counted at the list price, so sales divided by the price is the number of copies.
Worked example: a 300 page, 6 x 9 in paperback at $14.99 on Amazon.com earns $4.39 a sale. Break-even ACOS is $4.39 / $14.99 = 29.3%. You spend $100.00 and the ads sell $374.75, which is 25 copies. ACOS is $100.00 / $374.75 = 26.7% and ROAS is 3.75. Profit is 25 x $4.39 - $100.00 = $9.75, and the ACOS sits 2.6 points under break-even.
True profit with KU and read-through
KU earnings = KENP read from ads x KENP rate
Read-through earnings = readers x (r + r² + ... ) x earnings per later book
True profit = profit + KU earnings + read-through earnings
Here r is your read-through, one term for each later book. Readers are the buyers from the ads, plus KU readers who finished the book when you enter its KENP length. These are assumptions you supply, so the result is an estimate.
Add 3,000 KENP read from the ads at $0.00489 a page (the author-reported Amazon.com rate for August 2026): $14.68. If 40% of the 25 buyers read book two and 40% of those read book three, that is 25 x 0.56 = 14.0 later sales at $4.39: $61.46. True profit is $9.75 + $14.68 + $61.46 = $85.89, and the true break-even ACOS rises to 49.6%.
Reference
Break-even ACOS on Amazon.com at common list prices. Paperbacks: 300 pages, 6 x 9 in, black ink. Ebooks: 2 MB on the 70% plan, no VAT.
| List price | Royalty | Break-even ACOS | Break-even ROAS |
|---|---|---|---|
| $9.99 | $1.39 | 13.9% | 7.19 |
| $12.99 | $3.19 | 24.6% | 4.07 |
| $14.99 | $4.39 | 29.3% | 3.41 |
| $17.99 | $6.19 | 34.4% | 2.91 |
| $19.99 | $7.39 | 37.0% | 2.71 |
| List price | Royalty | Break-even ACOS | Break-even ROAS |
|---|---|---|---|
| $2.99 | $1.88 | 62.9% | 1.59 |
| $4.99 | $3.28 | 65.7% | 1.52 |
| $6.99 | $4.68 | 67.0% | 1.49 |
| $9.99 | $6.78 | 67.9% | 1.47 |
| $12.99 | $8.88 | 68.4% | 1.46 |
Below $9.99 a paperback earns 50%, so break-even drops sharply. KU pages and series read-through raise it.
Questions authors ask
What is a good ACOS for books on Amazon?
Any ACOS below your break-even ACOS makes money, so there is no single good number. A $14.99 paperback that earns $4.39 breaks even at 29.3%. A $4.99 Kindle ebook on the 70% plan earns $3.28 and breaks even at 65.7%. Ebooks can carry a much higher ACOS than paperbacks.
How do I calculate break-even ACOS for KDP?
Divide your royalty per sale by the list price. On Amazon.com a paperback earns 60% of the list price minus printing from $9.99, and an ebook on the 70% plan earns 70% of the price minus delivery. If the ad cost per sale equals the royalty, you break even.
What is the difference between ACOS and ROAS?
They are the same data flipped. Amazon Ads defines ACOS as ad spend divided by ad sales, and ROAS as ad sales divided by ad spend. An ACOS of 25% is a ROAS of 4. Break-even ROAS is the list price divided by the royalty: 3.41 for the $14.99 paperback above.
Do Kindle Unlimited pages read count toward ACOS?
No. ACOS only uses sales. Amazon Ads reports KENP read from ad clicks separately, within 14 days of the click, with an estimate of the royalties. That is why a KU book can show a high ACOS and still pay. Switch this calculator to Add KU and series to count them.
Why does my ad sales figure not match my KDP royalties?
Ad sales are what buyers paid for books sold within 14 days of an ad click, not what you earn. KDP reports royalties from every sale, ads or not, and pays a share of the price after printing or delivery. The two reports also update at different times.
Is it worth running ads at a loss on book one of a series?
It can be, if enough readers buy the later books. At a 40.0% ACOS the example paperback loses $40.25 on sales alone. With 40% read-through to two more books and some KU pages, the true profit is $35.89. Use your real read-through, not a hopeful one.
How do I work out my series read-through?
Compare sales of book two with sales of book one over the same few months, leaving a few weeks for readers to finish. For KU, divide the pages read of book two by its KENP length and compare it with book one the same way. Work out each step of the series separately; read-through usually rises after book two.
What KENP rate should I use?
KU has no fixed rate. KDP divides a monthly fund by all pages read that month and announces it in the middle of the next month. Amazon does not publish the per page rate. We start Amazon.com at $0.00489, the August 2026 rate reported by authors, the same rate our Kindle Unlimited earnings estimator uses. Use the rate in your own KDP report. Each reader counts for at most 3,000 KENP per book.
Before and after this step
- Previous stepBook royalty calculator
- Next stepKindle Unlimited earnings estimator
Read the guide
Related tools
Sources
Last verified against Amazon Ads' and KDP's own help pages. Amazon changes royalty rules and report definitions, so check the sources before you set a budget.
Amazon Ads
- Amazon Ads: What is advertising cost of sales (ACOS)? advertising.amazon.com
- Amazon Ads Help: Advertising cost of sales (ACOS) advertising.amazon.com
- Amazon Ads: What is Return on Ad Spend (ROAS)? advertising.amazon.com
KDP
- KDP Help: Advertising for KDP Books kdp.amazon.com
- KDP Help: Royalties in Kindle Unlimited kdp.amazon.com
- KDP Help: Paperback Royalty kdp.amazon.com
- KDP Help: Paperback Printing Cost kdp.amazon.com
- KDP Help: eBook Royalties kdp.amazon.com
- KDP Help: eBook List Price Requirements kdp.amazon.com