Break-even ACoS is just your margin, wearing an ads costume
ACoS — ad spend divided by ad-attributed sales — has a hard ceiling that most sellers never compute: the moment your ACoS passes your pre-ad profit margin, every advertised sale loses money. That ceiling is your break-even ACoS, and it is exactly your pre-ad profit divided by your price. Below it sits the number that should actually steer your campaigns: the target ACoS that still leaves the margin you intend to keep. This calculator derives both, converts them to ROAS, and turns them into the only bid number that matters — the maximum cost per click your conversion rate can support.
ROAS is the reciprocal: a 25% break-even ACoS is a 4.0× break-even ROAS. TACoS divides the same spend by all revenue, not just ad-attributed revenue — the break-even ceiling is the same money viewed store-wide, and a healthy account watches TACoS fall as organic sales grow.
Worked example
A $30 product with $9 of profit before ads breaks even at a 30% ACoS (3.33× ROAS). Keep a 10% margin and the target tightens to 20% ACoS (5.0× ROAS); at a 10% conversion rate, no click is worth more than $0.60. Bidding above that with a straight face requires a reason outside this product's economics — lifetime value, ranking strategy — named out loud, not assumed.
How to use this calculator
- Get an honest pre-ad profit from the Amazon FBA Calculator or TikTok Shop Calculator — with ads set to zero — and enter it here.
- Set the margin you intend to keep, not the margin you hope for.
- Cap bids at the max CPC shown; review whenever price, costs or conversion rate move.
- On TikTok, discount GMV Max's reported ROAS before comparing it to your target — its attribution counts organic and affiliate GMV too.