KDP ads, in plain words

KENP stands for Kindle Edition Normalized Pages. Because a real "page" changes with font size and device, Amazon converts every book to a standardized page count so page-reads can be paid the same way across every title.

Readers on Kindle Unlimited don't buy your book — they read it as part of a subscription, and Amazon pays you per KENP page actually read (recently about $0.004–0.005 per page). That income is reported separately from sales and lands later, which is why it's easy to leave out of your ad math and wrongly conclude a profitable book is losing money.

The Global Fund is a fixed pot of money Amazon sets aside each month to pay for Kindle Unlimited reading. At month-end Amazon divides that pot by the total number of KENP pages everyone read, and the result is that month's per-page rate.

Two moving parts — the size of the pot and how much everyone read — mean the rate can't be known until the month closes. It has historically stayed in a fairly tight band (roughly $0.004–0.005 per page in the US).

Kindle Unlimited (KU) is Amazon's subscription service — think "Netflix for books." Subscribers pay a flat monthly fee and read as many enrolled titles as they want.

Because a KU reader never buys the book, there's no sale and no sale royalty. Instead you earn from KENP page-reads. For many genres — romance, sci-fi, thriller — the majority of an author's income comes from KU reading rather than purchases, so any number that ignores it is missing most of the money.

ACOS (Advertising Cost of Sale) is the headline ad number: what percent of your ad-driven sales was eaten by ad cost. Spend $50 to make $100 in sales and your ACOS is 50%. Lower is better.

The catch: ACOS only looks at purchases. If your ads also send readers who borrow the book on Kindle Unlimited, that page-read income never appears in ACOS — so a campaign can look like a loser on ACOS while being clearly profitable once KENP is counted.

Break-even ACOS is the line between a profitable and an unprofitable ad. Roughly, it equals your royalty divided by your list price — for a book earning a 70% royalty it lands near 70%. Keep ACOS below it and the ad makes money; go above and it loses.

The reason nobody can pin it down cleanly is KENP. Your true break-even should include page-read income, not just the sale royalty — and that income shows up in a separate report, days later. A break-even that folds KENP in is exactly the number most dashboards never show.

TACOS (Total Advertising Cost of Sale) is ACOS done honestly: ad spend measured against all the money your book brought in — sales and KENP page-reads together — not just purchases.

Because it counts the page-read income ACOS ignores, TACOS is the number serious KDP advertisers actually watch. A single ugly week means little; TACOS trending down over six to eight weeks means each ad dollar is buying more total income over time — often because the ads are lifting your organic rank and the page-reads simply haven't caught up yet.

Attribution is Amazon deciding which sale or page-read to credit to which ad click. If someone clicks your ad today, borrows the book, and reads it over the following week, Amazon has to connect those reads back to today's click — and that linking keeps updating.

The practical rule: the last ~48 hours of data is still settling, so a number you read today can look different tomorrow. Judge campaigns on data that has stopped moving — a full settled week — not on the most recent day or two.