Amazon ACOS Calculator

The arithmetic

Advertising cost of sale is ad spend divided by the sales those ads are credited with: ACOS = spend ÷ attributed sales × 100. A 20% ACOS means twenty cents of advertising for every dollar of attributed revenue.

It is the inverse of ROAS, a 20% ACOS is a 5× ROAS, and Amazon uses it while nearly every other ad platform uses ROAS, which is why sellers running both constantly convert between them.

Attributed sales are those occurring within the attribution window after a click, which for Sponsored Products is seven days by default.

How that looks in practice

$1,200 of ad spend producing $6,000 of attributed sales is a 20% ACOS.

On the $29.99 product that is 200 attributed units at $6.00 of advertising each. Against $12.65 of pre-advertising contribution, those units contribute $6.65 rather than $12.65, profitable, but at roughly half the rate of an organic sale.

Now the same spend at a 45% ACOS: $2,667 of attributed sales, 89 units, $13.49 of advertising each. Those units lose $0.84 apiece, and the campaign is destroying contribution while showing sales.

The line between the two is the break-even ACOS, which for this product is 42.2%, and nothing about the campaign report tells you where it sits.

Where this breaks down

ACOS measures attributed sales, not incremental ones. A shopper who searched your brand name, clicked an ad and bought would very likely have bought anyway, and that sale is credited to the campaign in full.

Branded campaigns therefore show excellent ACOS while contributing little incremental revenue, and unbranded campaigns show worse ACOS while doing the actual acquisition work. Judging them by the same threshold systematically funds the wrong one.

It also ignores the organic rank that advertising builds, which is a real return arriving outside the attribution window.

What to do next

Calculate your break-even ACOS first and set targets relative to it rather than to a number borrowed from someone else's business. A 30% ACOS is excellent on a 45% margin product and ruinous on a 25% one.

Then separate branded from unbranded campaigns and judge them against different thresholds. Blending them into one account-level ACOS hides both the waste and the genuine acquisition.

ACOS against TACOS, and which decides anything

ACOS looks only at attributed sales. Total advertising cost of sale, TACOS, divides ad spend by total sales including organic, and it is the figure that shows whether advertising is building a business or renting one.

A product with a stable 25% ACOS and a falling TACOS is growing organically: advertising is driving rank and the organic share is rising. The same ACOS with a flat or rising TACOS means advertising is buying every sale and stopping it would stop the business.

That distinction is the most useful thing in Amazon advertising analytics and it takes one extra column to produce. Sellers who track ACOS alone can run a campaign for two years without ever learning which of those two situations they are in.

Advertising cost of sale is measured against advertising revenue only, which means it says nothing about total business profitability. A campaign at 25% ACOS looks fine and may still be losing money once cost of goods and fees are counted. Total advertising cost of sale, spend against all sales rather than attributed ones, is the figure that connects to the profit and loss.