The standard answer to a high ACOS is “lower your bids”. Sometimes that works. Often it doesn’t: in our study of 2,846 keywords, cutting the bid brought only 2 of 197 high-ACOS keywords under target. Here is why, and what actually moves the number.
What ACOS is made of
ACOS = cost per click ÷ (conversion rate × price)
Spend ÷ sales is the same as what one click costs, divided by what one click earns on average.
There are three ways to lower it: pay less per click, turn more clicks into orders, or earn more per order. A bid cut works on only the first — and it has a side effect. A lower bid wins fewer auctions and lower positions, so you lose clicks, and often the best-converting ones at the top of the results.
Why bid cuts often disappoint
In our data, 197 keywords that ran above a 38% target had their bids cut. Two got under target. The sixteen that kept selling went from 64% to 60%; the rest ended up paused. The conversion rate belongs to the search — who is typing it and what they want — and the bid doesn’t change that. What the cut changed was how often the ad showed.
Bid cuts do help where the cost per click is the problem: a keyword whose clicks got expensive in Q4, or one bidding well above what the click is worth. Work out that ceiling first: break-even bid = royalty per sale × conversion rate. If you are bidding far above it, cut. If you are near it, a cut will mostly cost you sales.
Five levers that move ACOS
1. Stop over-paying for product-page clicks. Across the account in our study, clicks from other books’ product pages converted at 5.0% and ran at 95% ACOS, against 14–16% conversion and 45–52% ACOS from search results:
| Placement | Share of spend | Conversion | ACOS |
|---|---|---|---|
| Top of search | 13% | 14.0% | 52% |
| Rest of search and other | 65% | 16.2% | 45% |
| Product pages | 21% | 5.0% | 95% |
Check your own placement report. If product pages look like this for you, lower the base bid and use the search placement adjustments to keep your search positions.
2. Negate the searches that spend without selling. After a fair test — about three divided by your conversion rate in clicks — add them as negatives. How to add negative keywords.
3. Move budget towards keywords with more history. Keywords made from searches with eleven or more orders ran at 38% ACOS in our study; those from one to three orders ran at about 57%. Same account, same books.
4. Compare match types on your own data. In this account, phrase match converted best (16.0% of clicks, 48% ACOS) against exact (13.0%, 57%) and broad (12.4%, 55%). That is one account, so treat it as a question to ask of yours, not a rule.
5. Work on the book page and the price. Conversion and price are two of the three parts of the formula. A cover that reads at thumbnail size, a clear description and a fair price all show up in ACOS.
AcosControl · Start freeSee which placement is costing you, on every keywordAcosControl shows top of search, rest of search and product pages on each keyword’s own row, for every period side by side.When not to lower ACOS
- When it’s under break-even. A lower ACOS is not the goal; profit is. Pushing a profitable keyword down can cost you sales you were making money on.
- During a launch. Early sales buy rank and reviews; many authors accept a higher ACOS for the first weeks on purpose.
- On Kindle Unlimited books. Page reads earn money that ACOS doesn’t count. KENP and ACOS.
- When TACOS is falling. If total sales grow faster than ad spend, the ads are working even at a high ACOS. ACOS vs TACOS.
Common questions
How do I lower my ACOS on Amazon ads?
Pay less per click where you are bidding above a click’s worth, convert more clicks (better placements, negatives, a stronger book page), or earn more per sale. ACOS = cost per click ÷ (conversion rate × price), so each lever works on one part.
Does lowering bids lower ACOS?
Only when the cost per click is the problem. In a study of 197 book keywords above target whose bids were cut, two got under target; the rest mostly lost clicks.
Why is my ACOS so high on Amazon book ads?
Usually low conversion rather than expensive clicks: product-page placements, broad searches from the wrong readers, or a book page that doesn’t convert. Check the placement report and search term report before cutting bids.
What is a good ACOS for a book?
One below your break-even ACOS — royalty per sale divided by list price. There is no universal number.
- ACOS = cost per click ÷ (conversion rate × price); a bid cut only touches the first part.
- Cutting bids brought 2 of 197 high-ACOS book keywords under target; it mostly cut clicks.
- Product pages converted at 5% and 95% ACOS, against 14–16% and 45–52% from search.
- Negate tested losers, move budget to keywords with more history, and compare match types.
- Don’t chase a lower ACOS below break-even, during a launch, or on KU books.