Book Math Tools

Break-Even ACoS Calculator for Books

Enter your book's price and royalty and your ad results to see your ACoS, the ACoS at which ads stop paying for themselves, and the highest bid that still breaks even.

Your ACoS
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Break-even ACoS
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ROAS
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Profit from ad sales
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Break-even CPC
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How ACoS and break-even ACoS work

ACoS = ad spend ÷ ad salesbreak-even ACoS = royalty per sale ÷ list price

Ad sales are counted at list price, but you only keep the royalty. So if your royalty is 30% of the price, spending more than 30 cents to make each dollar of sales loses money. The calculator also works out orders (sales ÷ price), profit (orders × royalty − spend), your cost per click, your conversion rate (orders ÷ clicks) and the break-even cost per click (royalty × conversion rate).

Worked example: a paperback

A 300-page 6" x 9" paperback costs $4.60 to print and sells for $16.99, so it earns $5.59 a copy. Break-even ACoS is $5.59 ÷ $16.99 = 32.9%.

The ads spent $85 on 340 clicks and sold $339.80, which is 20 orders. ACoS is $85 ÷ $339.80 = 25.0%, below break-even, so the ads earned $26.80 after paying for themselves. With 1 order per 17 clicks, each click is worth up to $0.33; the average click cost $0.25.

Worked example: a $3.99 ebook

A $3.99 ebook with a 1 MB file earns $2.69 at 70%, so break-even ACoS is 67.4%. Spending $60 for $119.70 of sales (30 orders) is an ACoS of 50.1%: high by paperback standards, but still $20.70 in profit. At 30 orders from 480 clicks the break-even bid is $0.17.

Getting ads under break-even

Look at keywords and targets one by one, not just the campaign total. A campaign at break-even often hides a few targets that sell well and many that spend without selling. Pause targets that have had 15-20 clicks with no sale, and lower bids on those above your break-even ACoS rather than pausing them straight away.

Raising the price raises break-even ACoS, sometimes a lot. On a paperback, every extra dollar of price is 60 cents more royalty, while printing cost stays the same. On ebooks, staying inside the $2.99-$12.99 range for the 70% royalty matters more than any bid change. If a series is involved, a reader bought through ads also buys later books, so a loss on book 1 can still be worth it; the series read-through calculator tells you how much you can afford to lose per sale.

Frequently asked questions

What is a good ACoS for books?

Any ACoS below your break-even ACoS makes money on the ad sales themselves. Because ebook royalties are a large share of the price (about 70% minus delivery), ebooks can run at an ACoS of 50-60% and still profit, while a paperback that keeps 25% of its list price loses money above 25%. Compare against your own break-even figure, not a general number.

Does ACoS include Kindle Unlimited page reads?

No. ACoS is ad spend divided by attributed sales, and page reads are not sales. Sponsored ads for books report KENP page reads separately. If your book is in KDP Select, add the page-read earnings to the sales figure (or treat your true ACoS as lower than shown) before deciding an ad loses money.

What is the difference between ACoS and ROAS?

They are the same ratio upside down. ACoS is spend ÷ sales; ROAS is sales ÷ spend. An ACoS of 25% is a ROAS of 4. Amazon's book ads show ACoS; many other ad platforms use ROAS.

How do I use the break-even CPC?

It is the most you can pay per click and still break even at your current conversion rate: royalty × orders per click. If you convert 1 in 20 clicks and earn $3.00 a sale, each click is worth $0.15. Bid below that, and lower it further if you want ads to make a profit rather than just pay for rank and reviews.

Sources

Rates last checked against KDP's help pages on 2026-10-16.

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