ACOS vs TACOS: Which One Actually Tells You If Your Book Business Is Profitable
ACOS divides your ad spend by the retail sale price Amazon credits to your ads — money you never keep. TACOS divides it by the royalties your ads actually generated. Here is the difference, a worked example, how to read TACOS (100% is break-even), and why it is the only ad metric denominated in money you keep.
ACOS is the number Amazon puts in front of you, and for a KDP author it is quietly misleading. It divides your ad spend by the retail sale value Amazon credits to your ads — the price the customer paid, not the money you keep. You never earn the sale price; you earn a royalty, a fraction of it. TACOS fixes that: it divides ad spend by the royalties your ads actually generated. That is the number that tells you whether a campaign makes you money.
The two formulas side by side
ACOS = Ad Spend ÷ Ad-attributed Sales (retail price) × 100
TACOS = Ad Spend ÷ Ad-generated Royalties (what you keep) × 100Same ad spend on top. The difference is the denominator: ACOS uses the customer's purchase price; TACOS uses your royalty on those purchases — plus the Kindle Unlimited pages your ads drove.
A note on the name. You will also see TACOS (Total ACOS) defined as ad spend ÷ your total sales, organic included. That version answers "how ad-dependent is my whole business?" — useful, but it still divides by the sale price, not your royalty. We use TACOS for the number that actually decides a campaign: ad spend ÷ the royalties your ads generated. Same instinct (look past a single campaign's ACOS), sharper denominator (money you keep, not the customer's price).
Why ACOS flatters every KDP campaign
On a $4.99 ebook at 70% you keep about $3.44. On a $12.99 paperback, after printing costs, you might keep $2. Amazon's ACOS is calculated against the $4.99 or the $12.99 — money that never reaches your bank account. So a "healthy-looking" 40% ACOS can hide a campaign that loses money the moment you count only your royalty. Authors who optimise to ACOS are optimising to a number that was never theirs.
Worked example: the campaign ACOS says to keep
One month, one title:
| Metric | Value |
|---|---|
| Ad spend | $500 |
| Ad-attributed sales (retail price) | $1,000 |
| Your royalty on those sales | $380 |
| Ad-driven KU royalties | $40 |
| Ad-generated royalties | $420 |
Judged on ACOS:
ACOS = $500 ÷ $1,000 = 50% → "efficient, keep spending"Judged on TACOS:
TACOS = $500 ÷ $420 = 119% → "you paid $1.19 for every $1 of royalty"ACOS calls the campaign efficient. TACOS shows you spent $500 to earn $420 of actual royalty — a loss. Only TACOS is denominated in money you keep.
Reading TACOS: 100% is the line
- Under 100% — the ads more than pay for themselves on the royalties they directly generated. You have room to scale.
- Around 100% — break-even on direct royalties. Can still be worth it if the ads lift your sales rank and drive organic sales you did not pay for (the halo effect).
- Over 100% — each ad-driven royalty costs more than it returns. Justified during a launch, or while organic halo is clearly picking up the slack — a warning sign if it persists for months.
The trend matters more than any single reading. A TACOS that falls month over month means each advertising dollar is converting into more of your real royalty.
Don't forget Kindle Unlimited
For KU-heavy titles, a large share of ad-driven income is page reads, not purchases. TACOS folds in the estimated KU royalties Amazon attributes to your ads, so it does not overstate how ad-dependent a KU title really is — see how KENP hides your real ad profit.
When to use which
- ACOS is Amazon's campaign-level lever — fine for comparing keywords, ads and bids inside the console, as long as you remember it is measured against sale price, not royalty. Judge it against your break-even ACOS, not your list price.
- TACOS is the profit question: for every euro of royalty an ad earned, how much did you spend to get it? It only makes sense at the book or account level, over weeks and months.
Where TrueRoyalties fits
TACOS is only trustworthy if "ad-generated royalties" is computed correctly — your real per-book royalty on ad-attributed sales, plus the KU royalties Amazon attributes to your ads, net of tax and converted to one currency. TrueRoyalties assembles exactly that from your KDP and Amazon Ads data and shows TACOS per book and globally, continuously — so you optimise to the money you keep, not the price the customer paid. Because the goal was never a low ACOS on one campaign — it was Net Profit = Royalties − Ad Spend, and TACOS is the ratio that gets you there.