Most break-even ACOS calculators stop at royalty ÷ price. An ad click on a book can earn more than that: Kindle Unlimited page reads and sales of the next book in a series. This one counts both. No sign-up, nothing you enter leaves your browser.
Your book
Kindle Unlimited from your ads — copy from Amazon Ads, same dates
Your line
Until you have a few months of your own Kindle Unlimited and series numbers, work to the strict line. An overestimated read-through lets you run an ACOS that burns the budget.
Rates checked against KDP Help on September 25, 2026: paperback, eBook, delivery costs. G201834330 · G200634500 · G200634560 · G201645410
ACOS is ad spend divided by ad sales, and ad sales are counted at the list price. So break-even ACOS is simple:
Break-even ACOS = what one ad sale earns ÷ list price × 100
For most products "what one sale earns" is the margin. For a book it can be three things:
Count only the royalty and you set the line too low: you switch off ads that were paying. Count everything and guess the numbers, and you set it too high.
That is why the calculator shows two break-even ACOS figures side by side:
Between the two lines, a campaign loses money on the book itself and wins only if your KU and series numbers are right. Until you have a few months of your own KU and read-through data, work to the strict line. An overestimated read-through lets you run an ACOS that burns the budget.
Amazon.com, checked against KDP Help on September 25, 2026:
| Format and price | Royalty | Source |
|---|---|---|
| Paperback, $9.99 and up | 60% × price − printing cost | KDP Help |
| Paperback, $9.98 and below | 50% × price − printing cost | KDP Help |
| Kindle, $2.99–12.99 | 70% × (price − delivery), delivery $0.15 per MB | KDP Help |
| Kindle, any other price | 35% × price, no delivery cost | KDP Help |
The calculator covers every KDP store — pick it and enter prices in its currency. In Japan, India, Brazil and Mexico the 70% eBook rate is for KDP Select books only (KDP Help); in Japan the Kindle price includes 10% consumption tax (KDP Help). Other marketplaces have their own paperback thresholds: 60% from £7.99 on Amazon.co.uk, from €9.99 in the EU stores, from CA$13.99 and AU$13.99 (KDP Help). Kindle delivery is £0.10 per MB in the UK and €0.12 in the EU; the minimum is one cent. In the EU and UK a Kindle list price includes VAT, and KDP deducts it before calculating the royalty (KDP Help); a paperback list price is entered without VAT (KDP Help). The 70% range on Amazon.com was widened to $2.99–$12.99 on July 7, 2026 (KDP Help).
Printing cost depends on the store, trim size, page count and ink, and the calculator works it out for you from KDP's printing cost tables — we checked it against KDP's own royalty calculator on 26 cases across all stores. Hardcovers are covered too: they print in 75–550 pages, black and white or premium color, in the US, UK, EU, Poland and Sweden; KDP prices Canadian hardcovers like Amazon.com. Australia has no standard color and no hardcover, Japan has no hardcover (KDP Help, KDP Help). For an 8.5×11 book with 75 pages it is $2.84 in black and white and $4.02 in standard color (KDP Help).
Amazon.com prices, 10% conversion rate. The paperbacks are our own books: 8.5×11, 75 pages, $24.99 — the calculator opens with the color one. We don't have books in Kindle Unlimited or series, so the Kindle rows are not our numbers: they show how KU and a series move the line, at the August 2026 rate of $0.00517 per page, with example page reads and read-through. Put in your own.
| Book | One ad sale earns | Break-even ACOS | Max cost per click |
|---|---|---|---|
| Kindle $4.99, 2 MB | $3.28 | 65.8% | $0.33 |
| Same + 1,500 KU pages read from 10 ad orders | $3.28 + $0.78 KU | 81.3% | $0.41 |
| Same + 2 more books in the series, 40% read on | $3.28 + $0.78 + $1.84 | 118.2% | $0.59 |
| Paperback $24.99, 8.5×11, color | $10.98 | 43.9% | $1.10 |
| Paperback $24.99, 8.5×11, black and white | $12.15 | 48.6% | $1.22 |
| Paperback $9.98, $2.30 printing | $2.69 | 27.0% | $0.27 |
| Paperback $9.99, $2.30 printing | $3.69 | 37.0% | $0.37 |
Two things stand out. A series can push break-even ACOS above 100%: the first book may cost more in ads than its price and still pay, because the money comes from books 2 and 3. And one cent on a cheap paperback changes the royalty rate — from 50% to 60%.
Rate per page. KDP announces only the monthly total of the KDP Select Global Fund, not a rate per page; your earnings depend on your share of all pages read (KDP Help). You see your own rate in your KDP reports: KENP royalties ÷ KENP pages read. Month by month the rate is collected by Written Word Media: for August 2026 it is $0.00517 per page on Amazon.com, and from March to August 2026 it moved between $0.0042 and $0.0052. The calculator starts at the August figure — replace it with yours.
Pages from your ads. Amazon Ads reports KENP metrics for book campaigns. Copy two numbers from Campaign Manager for the same campaigns and dates: KENP pages read and orders. The calculator divides one by the other. If the book is not in KDP Select, enter 0 pages.
Read-through is the share of readers who buy the next book. Take it from your own KDP reports over a few months: sales of book 2 ÷ sales of book 1. The calculator assumes every next book earns the same royalty as this one and that the same share moves on at each step. If you have no data yet, leave the series at 0 — a guessed read-through is how break-even gets set too high.
At break-even, you work for free. Our working rule: we keep ACOS under 30%.
But don't judge a campaign by ACOS alone. On August 1–3, 2026, one of our campaigns showed ACOS 44.47% — right at the 44% break-even of our color paperback at $24.99. By the console, it was time to cut it. Royalties for the same three days were $1,673.29 against $452.49 in ad spend: $1,220.80 net. The rest came from organic sales that the ads kept alive. The full breakdown is in Amazon Ads for Authors: judge campaigns by profit, not ACOS.
This page answers "where is my line". Whether a campaign stays below it week after week is a different question. AuthorLens shows royalties, ad spend including Sponsored Brands and video, and net profit for every book, and flags campaigns that cost more than they earn. We use AuthorLens daily and have a business relationship with it.
For monthly profit after ads and sales to your goal, use the KDP royalty and profit calculator.
The ACOS at which ads eat everything one ad sale earns. For a book that is the royalty per copy divided by the list price, plus Kindle Unlimited page reads and next-book sales that the same ads bring in. Below it, ads make money; above it, every ad sale loses money.
Anything below your own break-even ACOS pays; above it you lose money. Our working rule is to keep ACOS under 30%: at that level even our color paperbacks, with a 44% break-even, keep a margin.
Only with your own numbers. Until you have a few months of KU page reads from ads and read-through to the next book, work to the strict line — this book's royalty only. A guessed read-through is the fastest way to allow an ACOS that loses money.
No. ACOS is ad spend divided by ad-attributed sales at list price, and a Kindle Unlimited read is not a sale. That is why books in KDP Select can run a higher ACOS than the console suggests and still make money.
About 65.8% for a 2 MB file on Amazon.com: 70% of ($4.99 − $0.30 delivery) is a $3.28 royalty. If your ads bring 150 Kindle Unlimited pages per order, at the August 2026 rate of $0.00517 a page (Written Word Media) the line with KU rises to about 81.3% — but the strict line stays at 65.8%.
Break-even ACOS × list price × conversion rate. At 10% conversion one sale takes ten clicks, so a $24.99 black-and-white 8.5×11 paperback with a 48.6% break-even can afford up to $1.22 per click.
On Amazon.com the paperback royalty is 50% at $9.98 and below and 60% from $9.99. With a $2.30 printing cost, that one cent moves the royalty from $2.69 to $3.69 and break-even ACOS from 27% to 37%.