What Is ACOS? A Plain Guide for KDP Authors

ACOS, or advertising cost of sales, is the share of your ad-driven sales that you spent on Amazon Ads. The formula is ad spend divided by ad-attributed sales, times 100. Spend $40 to sell $100 of books through your ads, and your ACOS is 40%.

What ACOS means on Amazon Ads

Amazon’s own guide to ACOS calls it a metric used to measure pay-per-click advertising campaigns and gives the formula as ad spend divided by ad revenue, times 100. Its example is the simplest one possible: $50 spent, $100 earned, 50% ACOS.

Read it as a price tag. An ACOS of 25% means that for every $1 of books your ads sold, you spent 25 cents on clicks. An ACOS of 100% means the ads cost exactly as much as the books they sold. Above 100%, you paid more for the clicks than the readers paid for the books.

Amazon Ads shows ACOS for every campaign, ad group, keyword and search term. The formula is the same everywhere: the spend of that row divided by the sales Amazon credits to that row. That makes it handy for comparing two keywords side by side, and risky when you forget what the “sales” part actually measures.

How to calculate ACOS, step by step

You need two numbers from your Amazon Ads campaign report:

1. Spend: what you paid for clicks in the period.
2. Sales: the value of the books sold that Amazon attributes to those clicks.

Divide spend by sales and multiply by 100. If a campaign spent $18.40 last week and its sales were $61.33, the ACOS is 18.40 ÷ 61.33 × 100 = 30%. Amazon does this for you in the console, but doing it once by hand makes the next point obvious.

For books, “sales” has a precise meaning. KDP’s help page on advertising for KDP books describes it as the total value of your books sold within 14 days attributed to clicks on your ad. That is the value of the book sale, not the royalty that lands in your KDP account. A $14.99 paperback counts as $14.99 of sales even though you keep a fraction of it.

Why authors need a break-even ACOS, not a target from a blog

Amazon’s guide says break-even ACOS is directly linked to your profit margin, and that you have to keep ACOS below that margin to stay profitable. For a self-published book the margin is easy to name: it is your royalty as a share of the list price.

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

If you spend exactly that share of each sale on ads, the royalty and the ad cost cancel out. Spend less and the ad earns you money; spend more and every ad sale loses money. Because KDP pays different royalties for different formats and prices, each edition of each book has its own line.

Ebooks

KDP’s eBook Royalties page gives two plans. On the 35% plan the royalty is 35% of the list price (less any VAT). On the 70% plan it is 70% of the list price after VAT and a delivery cost, which the Digital Book Pricing Page sets at $0.15 per MB on Amazon.com. The 70% plan is only available inside a price band of $2.99 to $12.99 on Amazon.com; KDP raised the top of that band from $9.99 on July 7, 2026.

A $4.99 ebook with a 2 MB file on the 70% plan pays 70% × ($4.99 − $0.30) = $3.28. Its break-even ACOS is $3.28 ÷ $4.99 ≈ 66%. The same price on the 35% plan pays $1.75, and break-even falls to 35%.

Paperbacks

Print is where authors most often lose money without noticing. KDP’s Paperback Royalty page uses (royalty rate × list price) − printing cost. On Amazon.com the rate is 60% for list prices of $9.99 and up and 50% at $9.98 and below. The printing cost for a black-ink, regular-trim book of 110 to 828 pages is $1.00 plus $0.012 a page.

A 280-page paperback at $14.99 costs $4.36 to print and pays 60% × $14.99 − $4.36 = $4.63. Break-even ACOS: about 31%. A 200-page paperback at $8.99 costs $3.40 to print and pays 50% × $8.99 − $3.40 = $1.10, which puts break-even near 12%. Almost any ad will lose money on that one.

To run the numbers for your own books, the KDP royalty calculator works out the royalty from price, plan and printing cost, and the ACOS calculator turns it into a break-even ACOS.

Worked example: the same ACOS, two different results

Here are two campaigns with the same spend and the same ACOS. One sells a $4.99 ebook, the other a $14.99 paperback. Both use the royalties worked out above.

Amazon Ads shows both campaigns as 40% ACOS. One is making money and the other is losing it. The difference is not in the ads at all; it is in the royalty, which the ads console never sees. That is why a single target ACOS for a whole catalog rarely works.

ACOS, ROAS and TACoS compared

Amazon Ads reports show ACOS and ROAS; TACoS is a third number you will meet in advice for authors. All three use the same ingredients, divided in different ways.

ROASis ACOS upside down. Amazon’s guide says so directly: return on ad spend is ad revenue divided by ad spend. A 25% ACOS is a ROAS of 4; a 50% ACOS is a ROAS of 2. Pick whichever reads more naturally to you; they carry the same information.

TACoS, total advertising cost of sales, keeps the same ad spend but divides it by all of the book’s sales, ad-driven or not. Total sales come from your KDP reports rather than from Amazon Ads. If a book sells $400 in a month and $150 of that came through ads, a $60 spend is 40% ACOS but 15% TACoS. When TACoS falls while total sales hold or grow, more of the book’s sales are arriving without an ad click, a sign the ads may be helping it sell on its own too.

What ACOS leaves out for books

Kindle+ page reads

If your ebook is in KDP Select, it is also in Kindle+, the subscription that was called Kindle Unlimited until Amazon renamed it in October 2026. Part of what an ad earns then comes from page reads, not purchases. KDP Help is explicit that the ad sales attributed to your products do not include Kindle+ pages read. So a click that leads to a borrow, rather than a purchase, adds to spend and nothing to sales, which pushes ACOS up.

The ads dashboard does report those reads separately: an estimated number of KENP pages and estimated KENP royalties attributed to your Sponsored Products campaigns, counting pages read within 14 days after a click. For a book with many Kindle+ readers, add those royalties back before you judge a campaign. The KENP calculator turns a page count into money at a rate you choose.

The 14-day window and sales without a click

Amazon Ads credits a sale to a campaign when it happens within 14 days of a click on the ad. Readers who saw an ad, did not click, and bought the book later through search are not in that campaign’s sales. Neither are readers who clicked an ad for book one and then bought book two: KDP Help says sales of the advertised ASIN are the ones credited to the campaign.

Timing differences with KDP

KDP Help also lists why the two accounts disagree. KDP shows every sale of your books, whatever led to it; Amazon Ads shows only attributed ones. KDP records a paperback sale once it ships, while Amazon Ads records it on the purchase date. If you compare a single week, expect them not to match. Our guide to KDP reports explains which KDP report to use for which number.

What is a good ACOS for books?

The honest answer is the one Amazon gives brands: each one is different and will have a different target ACOS. For a book, “good” means below that edition’s break-even ACOS, with enough room left over to be worth the effort.

• Above break-even: each ad sale loses money. Fix it or stop it, unless you are deliberately investing in a launch or in read-through to later books in a series, and you have a limit in mind.
• Close to break-even: the ads pay for themselves and lift sales rank. Fine for a while, but there is little profit in it.
• Well below break-even: the ads make money on each sale. Here the risk flips: an ACOS that is very low can mean bids are too timid to win many clicks, and a slightly higher ACOS with far more sales may earn more in total.

Judge by profit in dollars, not by the percentage. A campaign at 20% ACOS that sells five copies a month can earn less than one at 45% that sells forty, if the book breaks even at 66%.

How to lower ACOS without killing sales

When a book sits above its line, these are the levers, roughly in the order worth trying:

1. Add negative keywords. Open the search term report and look for searches that spent money and sold nothing, or that have nothing to do with your book. Add them as negatives so the campaign stops paying for them.
2. Lower bids on the worst keywords and targets. Sort by ACOS against break-even rather than by spend. A keyword at twice your break-even needs a much lower bid or a pause.
3. Tighten targeting. Broad and automatic targeting find new searches, which is useful, but they also pay for searches that never sell. Move proven searches into exact match and keep exploration on a smaller budget.
4. Check placements. Top-of-search clicks can cost more than the rest. If a placement runs well above your line, lower its bid adjustment, or the base bid if the adjustment is already at 0%, since placement adjustments can only raise a bid.
5. Look at the book page. ACOS falls when more clicks turn into sales. A cover, title or description that does not match what the shopper searched for wastes every click you pay for.
6. Revisit the price. The price changes both halves of break-even. A paperback moved from $9.98 to $9.99 on Amazon.com goes from the 50% to the 60% royalty rate. For the 200-page book above, that moves break-even ACOS from about 16% to about 26%.

Our longer guide to Amazon ads for books covers campaign structure and bidding in more depth.

Seeing ACOS next to what each book really earns

The hard part of all this is not the formula. It is keeping, for every edition in every marketplace, a current break-even line and the real royalty next to the ad spend. Most authors do it in a spreadsheet: one column from Amazon Ads, one from the KDP report, per book and per month. That works, and it is worth doing even by hand.

If you would rather not rebuild it every month, the SelfPub Go ads modulecomputes each title’s break-even ACOS from its own royalty, price, format and marketplace and reads every campaign against that line, and royalty analytics reads the KDP report you already download to show profit per book after ads.

Formulas and rules in this guide are taken from Amazon Ads and KDP Help as of the date at the top of the page, using Amazon.com prices. Royalty rates, price bands and printing costs differ by marketplace and change from time to time; if something here no longer matches, the linked help pages are the source to trust.