ACoS vs ROAS — same metric, different lens
ACoS is the percentage of sales spent on ads — lower is better. ROAS is sales returned per dollar spent — higher is better. They mirror each other: 25% ACoS equals 4× ROAS. Amazon's interface defaults to ACoS, so most KDP authors think in those terms. A break-even ACoS for a typical paperback is roughly 33% (matching the 60% royalty minus print).
True ROI vs reported ACoS
Amazon's ACoS uses gross sales — but you only keep the royalty minus print cost. A 50% ACoS sounds bad, but if your royalty after print is $5 on a $12.99 book and your average sale costs you $6.50 in ads, you are losing $1.50 per book. This calculator does the real math.
Bid strategy for profitability
Start with low default bids ($0.20–$0.35) on auto campaigns. Move converting search terms into manual exact-match campaigns. Pause keywords with ACoS above 100% after 10+ clicks with no sale. Raise bids on keywords with ACoS below 30% to capture more volume. Run this calc weekly to track whether the overall account is profitable, not just individual campaigns.
When losing money on ads makes sense
Launch campaigns intentionally run at high ACoS to build sales rank and reviews. A book at 100% ACoS during launch can still be a winning long-term investment if it drives BSR low enough to generate organic sales for the next 12 months. Always separate launch ROI from steady-state ROI.
Frequently asked questions
What's a good ACoS for KDP?
Under 30% for steady-state Kindle, under 40% for paperback. Launch campaigns can tolerate 60–100% temporarily.
Does ACoS include organic sales?
No. Amazon's reported ACoS uses only ad-attributed sales. TACoS includes organic — many authors target TACoS under 10%.
Why is my ACoS so high?
Usually broad keyword targeting, weak cover/sample, or bidding above breakeven on terms that don't convert.
Should I pause unprofitable keywords?
Yes, after at least 10 clicks with zero sales or 1 sale and ACoS over 80%. Anything less is too small a sample.