How to calculate ACOS for Amazon ads
ACOS — advertising cost of sale — is ad spend divided by the sales those ads produced, as a percentage. Spend ₹2,50,000 to generate ₹10,00,000 of ad-attributed sales and your ACOS is 25%. It is the same relationship as ROAS, turned upside down: a lower ACOS is better, and 25% ACOS is a 4:1 ROAS.
What makes ACOS more useful than ROAS on Amazon is that it compares directly with something you already know. Your break-even ACOS is your product margin. If the margin is 30% and ACOS is 25%, the ads are profitable. If ACOS is 35%, they are not — and no amount of sales volume changes that arithmetic.
The ACOS formula
ACOS = (ad spend ÷ ad-attributed sales) × 100. Equivalent ROAS is 100 divided by ACOS. Both describe the same two numbers, so use whichever your team argues about less.
The part worth attention is "ad-attributed". Amazon credits sales within an attribution window after a click, which includes people who would have found the product anyway. On branded terms especially, a very low ACOS often means the ads are being paid to harvest demand you already had.
A seller spends ₹2,50,000 and Amazon attributes ₹10,00,000 of sales:
(₹2,50,000 ÷ ₹10,00,000) × 100 = 25% ACOS, the same as a 4:1 ROAS. On a 30% margin that clears break-even with five points to spare.
ACOS, TACOS and break-even
ACOS measures the ads in isolation. TACOS — total advertising cost of sale — divides ad spend by all sales, organic included, and is the better measure of whether advertising is building the business rather than just renting sales.
- Break-even ACOS equals your margin before ad cost. Below it the ads pay for themselves.
- Above break-even can still be right for a launch, where you are buying rank and reviews deliberately.
- Falling TACOS while sales grow is the healthiest pattern there is: organic is compounding.
- A very low ACOS on brand terms is usually harvesting, not growth.
Target ACOS by objective
There is no single right ACOS, only an ACOS that matches what the campaign is for. Decide the objective first, then the number follows.
| Objective | Target ACOS | Why |
|---|---|---|
| Launch and rank | Above break-even | Buying reviews and velocity on purpose |
| Profitable scale | Below margin | Every sale contributes on its own |
| Defending share | Near break-even | Keeping competitors off your listing |
How to lower ACOS
Most ACOS problems are targeting problems. Mine the search term report for terms taking spend and returning nothing, add them as negatives, and move the terms that do convert into their own campaigns where you can bid on them properly.
Then fix the listing, because ACOS is a conversion problem as much as a bidding one. Better images, a clearer title, answered questions and enough reviews all raise conversion rate, and a higher conversion rate lowers ACOS without a single bid change. If the catalogue is large enough that this stops being a manual job, marketplace ad management is where the structural work happens.