ACoS, Explained: What It Really Means and the Number You Should Actually Target

ACoS — Advertising Cost of Sales — is the first metric every Amazon seller learns and the one most people set wrong. It's simple to calculate and dangerously easy to misread, because a 'low ACoS' and 'making money' are not the same thing. Plenty of sellers proudly hit a tidy ACoS target while their product is barely breaking even, and others panic at a high ACoS that's actually buying profitable growth. Here's how to read the number correctly and pick a target tied to your margin, not to advice you saw in a forum.

What ACoS actually measures

ACoS is your ad spend divided by the sales those ads generated, expressed as a percent. Spend a tenth of the revenue an ad produced and your ACoS is 10%. It's a pure advertising-efficiency ratio: how much you paid to make a dollar of advertised sales. Crucially, it says nothing about whether that dollar of sales was profitable — it only describes the ad, not the business underneath it.

Why 'a good ACoS is 20%' is a trap

There is no universal good ACoS, because the right number depends entirely on your margin. A product with fat margins can tolerate a high ACoS and still profit; a thin-margin product is underwater long before it hits the same number. The single most useful figure is your break-even ACoS — the point where the ad spend exactly equals the profit you'd have on that sale before advertising. To find it, work out what's left after the referral fee (around 15% for many categories), fulfillment fees, and your product cost. That leftover, as a percent of price, is roughly the ACoS at which the ad neither makes nor loses money.

• ACoS below break-even — the ad is profitable on that sale; you have room to be more aggressive.
• ACoS at break-even — you're trading dollars; defensible for a launch, ranking push, or branded defense, but not for steady-state.
• ACoS above break-even — you're paying to make the sale, which can be worth it strategically but is a loss on that unit you must justify.

When a high ACoS is the right call

Spending past break-even isn't automatically a mistake. During a launch you're buying velocity and reviews to climb organic rank, knowing the early units lose money on ads so later organic sales don't need them. On branded keywords you may accept a higher ACoS to keep competitors off your own name. The mistake is running above break-even forever without a reason, or running there by accident because you never calculated where break-even was in the first place.

ACoS vs. TACoS — don't confuse the two

ACoS measures only advertised sales against ad spend. TACoS — Total Advertising Cost of Sales — measures ad spend against your total sales, ads plus organic. They answer different questions. A campaign can show a scary ACoS while your TACoS is falling, which usually means ads are doing their job: lifting organic sales so advertising becomes a smaller share of total revenue over time. Use ACoS to judge individual campaigns and TACoS to judge whether your advertising is building a self-sustaining business or propping one up.

Set your target the right way

Don't inherit a number. Set it from your own economics.

1. Calculate true unit profit before ads: price minus referral fee, fulfillment fees, product cost, and any prep or freight.
2. Convert that profit to a percent of price — that's your break-even ACoS.
3. Decide your target relative to it: below break-even for steady-state profit, at or above it only when you're deliberately buying rank or defense.
4. Revisit whenever fees or costs change, because a fee increase quietly lowers your break-even ACoS without warning.

Frequently asked questions

What is a good ACoS on Amazon?

There's no single good number — it depends on your margin. The metric that matters is your break-even ACoS, the point where ad spend equals your pre-ad profit on the sale. Anything below it is profitable; anything above it is a loss you should only accept for launches, ranking pushes, or branded defense. A 'low' ACoS on a thin-margin product can still lose money.

What's the difference between ACoS and TACoS?

ACoS divides ad spend by advertised sales only — it grades individual campaigns. TACoS divides ad spend by total sales, including organic — it shows whether advertising is a shrinking or growing share of your whole business. A high ACoS alongside a falling TACoS usually means ads are successfully driving organic growth.