What break-even ACOS means
Break-even ACOS is the highest advertising cost of sales your product economics can support before modeled profit reaches zero. It is not a universal Amazon benchmark: it depends on the contribution left after product cost, Amazon-related fees, fulfillment, returns and other non-ad costs.
The practical formula
Start with selling price. Subtract COGS, fulfillment, referral or seller fees, return reserve and other non-ad costs. The remaining contribution is your break-even advertising cost per order. Divide that amount by selling price to express the threshold as break-even ACOS.
Why actual ACOS can be misleading
An ACOS that looks low can still be unprofitable on a low-margin product. A higher ACOS can be sustainable on a high-margin product. Compare campaign ACOS with product-level break-even ACOS rather than relying on a generic target.
Use consistent campaign data
When evaluating PPC, use ad spend and attributed sales from the same campaign and date range. For TACOS, compare ad spend with total Amazon sales, including organic sales, over that same period.