Amazon Ads ACOS: a guide for KDP authors

You’ve launched an Amazon Ads campaign for your book and the clicks are coming in… but are you making money? The metric that helps answer that question is ACOS. Understand it properly, and you can avoid paying for clicks that bring nothing back.

What is ACOS?

ACOS (Advertising Cost of Sales) measures the share of your ad-attributed sales that you spend on advertising.

Example: you spend $30 on clicks and your ads generate $100 in sales. Your ACOS is 30%.

Important: these sales are measured at the book’s sale price, not your royalty. Pages read through Kindle Unlimited aren’t included in this calculation either: Amazon Ads reports them separately (KENP pages read and estimated royalties).

What ACOS should you aim for? Calculate your break-even point

There’s no universally “good” ACOS: it all depends on how much you earn per copy.

• Ebook priced at $4.99 earning about $3.20: break-even ACOS of approximately 64%.
• Paperback priced at $12.99 earning about $3 after printing: break-even ACOS of approximately 23%.

These examples are rounded: use your actual royalty from KDP’s pricing screen. Above this threshold, each ad-attributed sale costs you money; below it, the sale is profitable. A slightly higher ACOS may be acceptable at launch if advertising boosts your ranking, organic sales or Kindle Unlimited reads, but it should be a deliberate choice, not an accident.

Why your ACOS is too high

• Keywords that are too broad, attracting clicks from casual browsers.
• Clicks without sales: a keyword that keeps getting clicks but no sales burns through your budget.
• A listing that doesn’t convert: cover, description, price or lack of reviews. Ads bring readers in; your listing must persuade them.
• Bids that are too high relative to your royalty.

5 ways to reduce your ACOS

1. Analyze your search term report: it shows the exact searches that triggered your ads and which ones led to sales.
2. Add negative keywords to exclude searches that cost money without generating sales.
3. Move profitable terms to exact match in a manual campaign with a controlled bid.
4. Lower bids on expensive targets rather than switching everything off at once.
5. Improve your listing before increasing your budget: better conversion naturally brings ACOS down.

Understand your numbers without spending hours on them

Amazon Ads lets you export campaign reports. Bookstudio’s Amazon Ads Audit analyzes that export, calculates your ACOS keyword by keyword and identifies the ones eating up your budget without generating sales, with actionable recommendations.

And if your listing is holding back conversions, start with the free diagnostic: it evaluates your Amazon page using its ASIN.