ACoS is just a ratio
ACoS— advertising cost of sale — is simply ad spend divided by the sales those ads produced. Spend $30 to make $100 in ad sales and your ACoS is 30%. That's all it is: a ratio. It tells you nothing about whether you made money until you compare it against the margin the product had to begin with.
Break-even ACoS is your pre-ad margin
Here's the key idea. Take your sale price and remove everything exceptadvertising — the referral fee, the FBA fulfillment fee, your cost of goods, and any other per-unit cost. What's left, as a share of the price, is how much room you have for ads. That share is your break-even ACoS.
break-even ACoS = (price − referral − FBA fee − COGS − other) ÷ price
At exactly this ACoS an ad-driven sale earns zero profit. Spend a higher share on ads and the sale loses money; spend less and it profits. It's the same contribution margin from the true-profit guide, viewed through the lens of what you can afford to bid.
Target ACoS is the number you aim for
Break-even is the ceiling; you don't want to run there or you make nothing. Your target ACoS sits below break-even by however much profit you want to keep on each ad sale. A product launching hard might target close to break-even to buy rank; a mature product might target well under it to bank margin. Either way, target ACoS is a decision — break-even ACoS is the constraint that decision has to respect.
TACoS is the number that judges the business
One more metric matters over the long run. TACoS — total ACoS — is ad spend divided by total sales, organic and advertised together. ACoS grades a campaign; TACoS grades the whole account. When TACoS trends down over months, it means your ads are lifting organic rank and the business is leaning less on paid traffic — the healthiest pattern there is.
Turning the numbers into bids
Knowing your targets, the day-to-day work is moving each keyword toward them:
- Raise bids on keywords converting below target ACoS — they have room to buy more sales profitably.
- Lower bids on keywords running above target — they're eating margin.
- Cut the spenders with clicks but zero orders — they're pure loss.
- Keep exploring new keywords that haven't gathered enough clicks to judge yet.
Done by hand across hundreds of keywords this is a spreadsheet nightmare. A bid optimizer computes the right bid for every keyword from one account-level target ACoS, rate-limits the changes so a bad day can't swing your bids wildly, and shows the reasoning behind each move.
FAQ
What is ACoS?+
ACoS (Advertising Cost of Sale) is ad spend ÷ ad sales, expressed as a percentage. A 25% ACoS means you spent $25 in ads for every $100 of ad-attributed revenue. On its own it says nothing about profit — you have to compare it to your break-even ACoS.
What is break-even ACoS?+
Break-even ACoS is your contribution margin before advertising, as a percentage of price — everything left after referral fee, FBA fee, cost of goods and other per-unit costs, divided by the sale price. It's the exact ACoS at which an ad-driven sale earns zero profit: spend more than that on ads and the sale loses money; spend less and it profits.
How is break-even ACoS different from target ACoS?+
Break-even ACoS is the ceiling — the most you can spend before a sale stops being profitable. Target ACoS is what you actually aim for, set below break-even by however much profit you want to keep on each ad sale. If your break-even ACoS is 35% and you want to keep a third of the margin, you'd target roughly 23%.
What is TACoS and why does it matter?+
TACoS (Total ACoS) is ad spend ÷ total sales — organic and advertised combined. Where ACoS judges a campaign, TACoS judges the whole business. A falling TACoS over time is the signal you want: it means your ads are driving rank and organic sales are carrying more of the load.