ACOS, TACOS and ROAS: which one actually tells you to stop spending
Three metrics, one decision. Here is how they relate, why a healthy ACOS can still lose money, and how to compute the only threshold that matters — your break-even ACOS.
7 min read
ACOS, TACOS and ROAS all describe the same transaction from different angles. Used carelessly, they let a campaign look fine while the business loses money on every order.
The three definitions
- ACOS = ad spend ÷ ad-attributed sales. Efficiency of the ad itself. Lower is better.
- ROAS = ad sales ÷ ad spend. The same number inverted. ACOS of 25% is a ROAS of 4×.
- TACOS = ad spend ÷ total sales, organic included. How dependent the whole business is on paid traffic.
Why a good ACOS still loses money
ACOS says nothing about your margin. If your contribution margin before advertising is 28%, then spending 30% of revenue on ads makes the sale unprofitable — even though a 30% ACOS sounds respectable and the ROAS of 3.3× looks healthy on a dashboard.
The threshold you actually need is the break-even ACOS, and it is simply your contribution margin before advertising. Above it you lose money per incremental order; below it you have headroom. Everything else is commentary.
What TACOS adds
ACOS can look excellent while TACOS climbs — which means paid sales are replacing organic ones rather than adding to them. A business whose TACOS rises quarter after quarter is renting its demand. The useful question is not "is my ACOS good?" but "is ad spend buying organic rank that persists after the spend stops?"
The diagnostic order
When a campaign underperforms, the fault is usually upstream of bidding:
- CTR below ~0.3% — the listing is not earning the click. Main image, title, price and review count. More budget will not fix this.
- CVR low with healthy CTR — traffic arrives and does not buy. Price competitiveness, A+ content, or keyword intent that does not match the product.
- Both healthy, ACOS above break-even — now it is a bidding problem, and now bid changes will work.
Our Advertising AI reads all six metrics together and names which of these three layers is costing you money, rather than reporting the numbers back to you.
Campaign architecture, keyword strategy, bidding and the weekly optimisation cadence are covered end to end in the Amazon Advertising Playbook.