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Amazon Ads for Books: Know Your Break-Even ACoS Before You Bid

Your break-even ACoS is fixed by your price and royalty before you spend a cent on ads. Work it out first, turn it into a maximum bid for the conversion rate you actually see, and only then decide how much to spend.

Published October 17, 2026. Figures are calculated from KDP's published rates when the page is built.

ACoS is ad spend divided by the sales the ads are credited with. For an author the trap is in the word "sales": it means what readers paid, while you keep only the royalty. A book that sells $100 of copies through ads did not make you $100.

That gap is the whole idea of break-even ACoS. If you keep 30 cents of every dollar a reader pays, you can spend up to 30 cents in ads to make that dollar of sales and come out level. Spend 31 cents and each ad sale loses money.

No ad data goes into that formula. It is a property of the book and its price, which means you can know it before launching a single campaign.

Two books, two very different ceilings

Take a $4.99 ebook with a 2 MB file on Amazon.com. At the 70% royalty, KDP deducts a delivery cost of $0.30 for that file size (from the Digital Book Pricing page), leaving $3.28 per sale. Break-even ACoS is $3.28 ÷ $4.99 = 65.7%.

Now a 300-page, 6" x 9" paperback on cream paper at $14.99. KDP charges $4.60 to print it on Amazon.com and pays 60% at that price (paperback royalty page), so the royalty is $14.99 × 0.6 − $4.60 = $4.39. Break-even ACoS is 29.3%.

Same author, possibly the same book in two formats, and the ebook can tolerate more than twice the ACoS. A campaign reporting 40% ACoS is profitable for the first and losing money on the second. So there is no single "good ACoS" for books; the only benchmark that means anything is your own. The break-even ACoS calculator works it out from your price and royalty, and also gives the inverse, break-even ROAS (1.52 for the ebook, 3.41 for the paperback).

From ACoS to a bid: the ladder

ACoS tells you whether ads paid off after the fact. When you set a bid you need something different: what one click is worth. A click is worth your royalty multiplied by the chance that the click turns into a sale.

Conversion rate is the input you can't calculate in advance; it comes only from your own campaign data. So the table uses three example rates, not typical ones. Read across to find the row nearest to what your reports show.

Three things stand out once the numbers are side by side.

First, conversion matters as much as price. Tripling the conversion rate triples the bid you can afford, while break-even ACoS doesn't change at all. A better cover or a sharper description raises your ceiling on every keyword at once.

Second, the paperback's lower break-even ACoS doesn't mean a lower bid. Its royalty in dollars ($4.39) is higher than the ebook's ($3.28), so at the same conversion rate a paperback click is worth more. ACoS compares spend with list price; bids compare spend with royalty.

Third, a bid at break-even buys sales that earn you nothing. The "keeps $1.00" columns treat $1.00 of each royalty as yours and spend only the rest on clicks: the ebook's royalty is then $2.28 and the paperback's $3.39, multiplied by the same conversion rate. Choose your own margin; the method is the same.

What monthly ad spend does to break-even

Ads also change the bigger question of when the book earns back what it cost to make. Suppose the ebook cost $1,500.00 to produce (cover, editing, formatting) and sells 60 copies a month at $3.28 each. The book break-even calculator treats ad spend as a monthly cost that sales must cover before anything goes toward the $1,500.00.

The table holds sales at 60 a month in every row, which is the honest way to read it: it shows what the ads cost if they add nothing. Then ask, for each budget, how many extra sales the ads must bring in just to pay for themselves. At $100.00 a month it is 31 copies on top of the 60; at $200.00 it is 61, more than the book sold without any ads. If your ad reports show fewer attributed orders than that, the ads are pushing your break-even further away. The 458 copies needed to repay the $1,500.00 don't change; ads only add their own copies on top, every month.

The same logic applied to an income goal

Say the goal is $500.00 a month from a catalogue of 3 ebooks like this one. Without ads, the income goal calculator puts it at 153 copies a month, 5 a day across the catalogue, or 1.7 per book per day. Add $200.00 a month of ads and sales have to cover $700.00: 214 copies a month, 7 a day.

The ads have to close that gap themselves. If $200.00 of clicks at your bid and conversion rate brings in at least 61 extra sales a month, the ads pay their way toward the goal. If it brings fewer, the goal is further away with ads than without.

A short routine before each bid change

1. Check the royalty for each format at its current price. A price change moves every number on this page; the price change calculator shows by how much.
2. Work out break-even ACoS per format, once, and write it next to the campaign name.
3. From your own report, take orders ÷ clicks for the targets that have enough clicks to mean something, and read your break-even bid off the ladder.
4. Decide how much of each royalty you want to keep, and bid below that line.
5. Put the monthly budget into the break-even and income goal numbers, and compare the copies it must sell with the orders the ads actually report.

Two cases change the royalty you put into step 1. If the book is in KDP Select, Kindle Unlimited readers pay you in page reads rather than sales, and the KENP calculator converts those to dollars. And for book 1 of a series, the read-through calculator gives a per-reader value across the series, which can justify a bid that loses money on book 1 alone, provided the later books really do sell.

More guides

• Co-Writing a Book on KDP: Who Gets Paid and How to Split It
• Kindle's 70% Royalty Now Goes Up to $12.99: What to Reprice
• What KDP Charges to Print a Paperback, With Every Table