Break-Even ACOS Calculator for Books

Your break-even ACOS is your royalty per sale divided by your list price. Below it, each ad sale earns more royalty than the ad cost. Above it, each sale costs more than it earns.

ACOS leaves out one thing many KDP authors rely on: Kindle Unlimited (now Kindle+) page reads. Amazon reports them separately, so a campaign can look unprofitable on ACOS and still make money. This calculator counts both.

Built by a KDP author with 10 books and 25,000+ copies sold, who got tired of doing this math by hand.

Free, no signup. US marketplace, US dollars.

What is ACOS?

ACOS (advertising cost of sales) is your ad spend divided by the sales your ads brought in, shown as a percentage.

ACOS = ad spend ÷ ad sales × 100

If you spend $50 and your ads bring in $200 of sales, your ACOS is 25%. ROAS (return on ad spend) is the same ratio turned over: ad sales ÷ ad spend. A 25% ACOS is a ROAS of 4.

Amazon counts ad sales at the price the reader paid, not at your royalty. That's why a book needs its own break-even ACOS instead of a target borrowed from other Amazon sellers.

How to find your break-even ACOS for a book

Break-even ACOS = royalty per sale ÷ list price × 100

At your break-even ACOS, the ad cost of a sale equals the royalty from that sale. A $4.99 ebook earning $3.40 breaks even at 68.1% ACOS. A $14.99, 250-page paperback earning $4.99 breaks even at 33.3%.

Work out a separate break-even for each format. Ebooks on the 70% royalty option keep a much larger share of the price than paperbacks, so they can carry about twice the ACOS.

Break-even ACOS by format

How these are worked out: ebooks at the 70% royalty option, less Amazon's stated average delivery cost of $0.06 (larger files cost more). Paperbacks at 60% of list price, less KDP's printing cost for black ink, regular trim ($1.00 plus $0.012 per page). Your own numbers may differ; use your royalty from KDP.

What is a good ACOS for books?

There's no single good ACOS for books. A good ACOS is any ACOS below your book's break-even, and that depends on your royalty. For ebooks on the 70% option, break-even is usually around 68% to 69%. For paperbacks, it's often around 30% to 35%, lower for long books with higher printing costs.

If your book is in Kindle Unlimited, ACOS alone undercounts what your ads earn. Count your page-read royalties too (Step 2 above does this).

What is KENP, and why ACOS leaves it out

KENP (Kindle Edition Normalized Pages) is how Amazon counts pages read by Kindle Unlimited readers. Amazon's reports now call the program Kindle+. You're paid for each page read, at a rate that changes every month.

Amazon Ads doesn't count those page reads as ad sales, so they never show up in your ACOS. Instead, for Sponsored Products campaigns, the Amazon Ads console reports them separately:

• KENP read: estimated pages read by readers who borrowed your book after clicking your ad.
• Estimated KENP royalties: the royalties from those pages, for readers who clicked your ad and read within 14 days.

For a Kindle Unlimited book, add the estimated KENP royalties to your sale royalties before deciding whether a campaign makes money. That's what Step 2 does.

How organic sales can make a campaign worth it

Ad sales are only the sales Amazon can tie to an ad click. They aren't the whole picture. Every sale your ads bring in can lift your book's Best Sellers Rank, and a better rank puts the book in front of more readers who find it without an ad. Those organic sales never show up in your Amazon Ads reports.

So a campaign that looks slightly unprofitable here, even counting Kindle Unlimited reads, can still be worth running if it's lifting your book's total sales. The same goes for readers who go on to buy the next books in a series.

The catch: you can't see this lift in the ads console, so check it rather than assume it.

• Compare your book's total sales in your KDP reports with your ad spend over a few weeks. If total sales rise when ads run and fall when they stop, the ads are helping.
• Track TACoS (below). If your ad spend stays steady and TACoS goes down, organic sales are growing.

If total sales don't move when your ads run, there's no organic lift, and a campaign that loses money on ad sales and page reads is simply losing money.

ACOS vs TACoS

TACoS (total advertising cost of sales) is all your ad spend for a book divided by all of that book's sales, from ads and organic, for the same period.

TACoS = total ad spend ÷ total sales × 100

For example: in one month a book spends $300 on ads, its ads bring in $600 of sales, and it sells $1,500 in total. Its ACOS is 50% and its TACoS is 20%.

ACOS tells you how one campaign is doing. TACoS tells you whether ads are lifting the whole book. If your ad spend stays steady and TACoS goes down over time, total sales are growing faster than ad spend, which usually means ads are helping organic sales. TACoS is a book-level number, so this calculator, which works one campaign at a time, doesn't calculate it.

What this calculator doesn't include

• Organic sales your ads help create (see How organic sales can make a campaign worth it, and TACoS above).
• Sales of your other books, like the next books in a series.
• Sales or page reads after Amazon's 14-day attribution window.
• Different royalties by format or marketplace. Use one book and format per campaign, or an average royalty.