Author Ads Pro

Free tool

ACoS calculator for KDP authors

Work out ACoS, ROAS and ACoR for a book ad, then see the true ACoS once Kindle Unlimited page reads and later books count.

ACoS (what Amazon shows)

139%

Ad spend ÷ attributed sales.

True ACoS (series)

62%

Ad spend ÷ every royalty the ads earned. Under 100% is profit.

ROAS

0.72x

Sales ÷ spend

ACoR

198%

Spend ÷ sale royalties

Classic break-even

70%

Your royalty rate

Profit

$156.00

All royalties − spend

The formulas

  • ACoS = spend ÷ attributed sales
  • ROAS = attributed sales ÷ spend
  • ACoR = spend ÷ (sales × royalty rate)
  • True ACoS = spend ÷ (sale royalties + KU royalties + later-book royalties)

ACoS and ROAS describe the ad. ACoR and true ACoS describe your business. For a standalone book sold outright, ACoR is enough. For a Kindle Unlimited series, only true ACoS sees the page reads and the books readers go on to.

Where the inputs come from

Spend and sales are in the Amazon Ads console. KU royalties are in the estimated KENP royalties column where your reports have it, or pages read × the month's KENP rate. Later-book royalties come from your read-through: the read-through calculator works them out.

Run your own report through the Kindle Author Ads Analyzer

Free, runs in your browser, no signup. See which terms to negate, which bids to move and which keywords pay across the series.

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Questions

What is the ACoS formula?

ACoS = ad spend ÷ attributed sales × 100. $50 of spend that drove $100 of sales is 50% ACoS. ROAS is the inverse: sales ÷ spend, so 2.0x in the same example.

What's the difference between ACoS and ACoR?

ACoS divides spend by sales at list price. ACoR (advertising cost of royalties) divides spend by the royalties you actually keep. For a 70% royalty book, ACoR is about 1.43 times ACoS. Under 100% ACoR, the sale royalties alone cover the ads.

What is true ACoS?

Ad spend divided by every royalty the ads earned: sale royalties, Kindle Unlimited page reads, and later books readers go on to buy or borrow. It's the measure that matters for a KU series.

Why is my ACoS over 100% but my royalties are up?

Usually page reads and read-through. Neither shows in ACoS. Add your estimated KENP royalties and later-book royalties to see the real return.

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