Break-even ACOS shows how much of an Amazon order’s revenue can be spent on attributed advertising before modeled profit reaches zero. It is a ceiling, not a recommended target.
Formula and decision rule
Break-even ACOS = profit before advertising ÷ attributed sales revenue × 100. A profit-preserving target can be estimated as (profit before ads − desired profit) ÷ revenue × 100. Use contribution profit, not gross margin, so referral, fulfillment, product, inbound, storage, returns and other variable costs are already deducted.
Worked example
A $30 order has $9 of contribution profit before ads. Break-even ACOS is $9 ÷ $30 = 30%. If the seller wants to retain $4.50 profit, the planning target becomes ($9 − $4.50) ÷ $30 = 15%. Spending at 30% would leave no modeled profit for overhead or unexpected losses.
ACOS versus TACOS
ACOS divides attributed ad spend by attributed ad sales. TACOS divides ad spend by total sales, including organic sales. ACOS evaluates campaign economics; TACOS helps show how dependent the whole product is on advertising. Neither metric replaces cash-flow or inventory analysis.
Costs sellers commonly omit
- Expected refund and unsellable-return losses.
- Inbound placement, prep and labeling.
- Storage and aged-inventory charges allocated per sold unit.
- Coupons, promotions and account-level software.
- Agency or creative costs that are outside Amazon Ads.
Use the calculator
Enter verified product costs in the Amazon FBA Calculator. It reports contribution profit, break-even ACOS, target-margin price and inventory turns from the same scenario.
Primary sources
Frequently asked questions
Can ACOS be higher than break-even temporarily?
Yes, for a launch or ranking experiment, but that is an intentional investment. Set a budget and measurement window rather than calling an unbounded loss profitable.
Does break-even ACOS include fixed overhead?
Only if the seller allocates that overhead into the per-order cost inputs. The basic formula normally measures contribution profit before fixed business costs.
Change log
Published August 4, 2026 with an auditable ACOS formula and a link to the editable FBA scenario calculator.