Open Seller Central. Click "Advertising." Look at the column labeled ACoS. You see a number — maybe it's 18%, maybe it's 47%, maybe it's a wildly different number every time you blink. You ask yourself the same question every Amazon seller has asked since 2014: is that good?
The honest answer is the question itself is incomplete. ACoS in isolation doesn't tell you whether your campaigns are working. It tells you a ratio. Whether the ratio is good or bad depends entirely on things ACoS doesn't measure — your contribution margin, your category dynamics, your campaign goal, and whether you're hunting new customers or defending existing ones.
[Settles in.] So let's actually define this metric properly. What it is, how it's calculated, what a good number looks like for different categories, why "lower" isn't always "better," and the six mistakes sellers consistently make when they treat ACoS as the single number that matters.
What ACoS Actually Stands For
ACoS = Advertising Cost of Sale. It is the percentage of ad-attributed revenue that was spent on the ads that generated it.
The math is dead simple:
ACoS = (Ad Spend ÷ Ad-Attributed Revenue) × 100
If you spent $100 on ads and Amazon attributes $400 in sales to those ads, your ACoS is $100 / $400 = 25%. That's it. There's no hidden formula, no Amazon secret sauce. It's a ratio of one number to another.
What makes ACoS tricky isn't the formula — it's that the formula leaves out everything that matters: your costs, your margin, your organic sales, and your goals. The number on its own is just a ratio. The interpretation requires context that ACoS does not provide.
How to Calculate ACoS
You almost never need to calculate ACoS by hand because Amazon's ad console shows it for you on every campaign, every ad group, every keyword. But understanding the inputs matters because Amazon's default view aggregates in ways that can hide problems.
If you're only looking at account-level ACoS, you're missing where the actual problem lives. A healthy 22% account-level ACoS can be made up of one campaign at 8% (great) and another at 65% (catastrophic) blending together to look acceptable. The blended view hides the disaster.
What's a Good ACoS on Amazon?
The short answer is: any ACoS lower than your contribution margin is profitable; anything higher is losing money on that ad-attributed sale. The long answer is more interesting.
Your break-even ACoS equals your contribution margin percentage. If your contribution margin (revenue minus COGS, minus Amazon referral fee, minus FBA fees, minus returns) is 35%, then a 35% ACoS breaks even on that ad sale. Below 35% is profitable on attribution; above 35% loses money on attribution.
Selling price: $30.00
COGS: $9.00
Amazon referral fee (15%): $4.50
FBA fulfillment: $5.50
Returns reserve (~5%): $1.50
Contribution margin: $9.50 (~32%)
Break-even ACoS: ~32%. Spend $32 on ads and you'll generate $100 in sales, $32 in contribution margin, and zero net profit on that incremental ad-attributed revenue. Anything tighter than 32% is profitable.
That's the floor. The ceiling depends on what the campaign is for. Most established brands target an ACoS of 15 to 25% on harvested converters, which keeps real profit in the equation. Hunter campaigns (broad match prospecting) might run 35 to 50% and be acceptable if you're explicitly buying market share. Brand-defense campaigns (your own branded terms) should run under 10% — if you're paying more than that to rank for your own brand, something is structurally wrong.
ACoS vs TACoS: The Difference Sellers Get Wrong
This is the single most-misunderstood Amazon PPC concept, so let's be precise. ACoS measures ad spend against ad-attributed revenue only. TACoS — Total Advertising Cost of Sale — measures ad spend against total Amazon revenue, including organic sales.
ACoS: Ad Spend ÷ Ad-Attributed Revenue
Tells you: efficiency of attributed ad-driven sales.
TACoS: Ad Spend ÷ Total Revenue (ad + organic)
Tells you: ad-spend efficiency relative to total business size.
Why TACoS matters: if your ad spend is staying flat but your organic sales are growing, TACoS goes down — even if ACoS stays the same. That's the actual signal that your account is getting healthier.
For established brands, TACoS is the more meaningful metric. ACoS measures whether your ad campaigns are efficient at the level of attribution. TACoS measures whether your overall business is using ads efficiently relative to its real size. (For the full breakdown of why TACoS often lies, see why your TACoS is lying to you.)
Why a "Low ACoS" Isn't Always Good
Conventional wisdom says: lower ACoS = better campaigns. That's wrong in three specific cases, and getting tricked by it costs brands more than the high-ACoS campaigns they're trying to optimize away.
ACoS is a ratio. Profit is a dollar amount. Optimize for the second one — and use ACoS only as a leading indicator of whether you're on track.
How to Lower ACoS (Without Killing What Works)
If your ACoS is genuinely too high — meaning above your contribution margin and not justified by a strategic reason like prospecting — there are four things to do, in order. Skip ahead at your peril.
What you should NOT do: blindly lower bids. Lowering bids drops your ad placements, drops your impression share, and often increases ACoS because you're competing in worse auction positions. (Full breakdown: how to lower ACoS on Amazon — without killing the campaigns that actually work.)
ACoS Benchmarks by Category
"Good ACoS" varies meaningfully by category because contribution margins vary meaningfully by category. Rough benchmarks from typical established brand accounts:
Supplements: 15–25% (high margin, high competition)
Beauty: 18–30% (creative-driven conversion)
Apparel: 25–40% (lower margin, variant complexity)
Home goods: 20–35% (mid-margin, broad keyword pool)
Electronics: 8–18% (low margin, branded search dominant)
Food & beverage: 15–30% (subscription mix changes math)
Health & wellness: 18–28% (regulated category, premium pricing)
Pet products: 20–35% (margin tighter than category looks)
These are ballpark numbers, not laws. Within any category, individual brand ACoS varies based on listing quality, brand recognition, organic ranking strength, and the mix of branded vs non-branded ad spend. Use category benchmarks as a sanity check, not a target.
Six Common ACoS Mistakes
And finally — the recurring patterns. These are the six things brands consistently get wrong when they treat ACoS as the metric that matters.
The Bottom Line
ACoS is the ratio of ad spend to ad-attributed revenue, calculated as ad spend divided by ad-attributed revenue. A "good" ACoS is any number below your contribution margin — but ACoS in isolation is an incomplete metric. Pair it with TACoS, with contribution dollars, and with category-specific benchmarks if you want a real picture of whether your campaigns are doing their job.
And remember: ACoS is a ratio, profit is a dollar amount, and growth is a strategic decision. Optimizing for the ratio without thinking about the dollars or the strategy is how brands end up with "great" ACoS and shrinking businesses.
[Final stage direction: the brands quietly winning at Amazon advertising in 2026 are not the ones obsessing over ACoS. They are the ones tracking contribution dollars, tracking TACoS, and using ACoS as a leading indicator rather than a scorecard. Pick the right scorecard. The right decisions follow.]
FAQ
ACoS stands for Advertising Cost of Sale. It measures the ratio of ad spend to ad-attributed revenue on Amazon, expressed as a percentage. If you spend $20 on ads and generate $100 in attributed sales, your ACoS is 20%. It is the most commonly tracked Amazon PPC metric, and also the most commonly misused — because by itself, ACoS does not tell you whether your campaigns are profitable.
A good ACoS depends entirely on your contribution margin. As a rough rule, your break-even ACoS equals your contribution margin percentage. For a product with a 35% contribution margin, a 35% ACoS is break-even, anything below is profitable. Most established brands target an ACoS of 15 to 25%, but the right number depends on your category, your goals (profitability vs. growth), and whether the campaign is defending branded terms or hunting new customers.
Start with the search term report — it is the single fastest source of wasted ad spend. Add negative keywords for irrelevant search terms that are draining budget without converting. Then audit your campaign structure for cannibalization (multiple campaigns bidding on the same terms), placement modifiers, and bid strategy. Finally, improve your listing conversion rate, because a higher conversion rate mathematically lowers ACoS even at the same bid level.
ACoS measures ad spend against ad-attributed revenue only. TACoS (Total Advertising Cost of Sale) measures ad spend against total Amazon revenue, including organic sales. TACoS is the more meaningful metric for established brands because it reflects how efficiently your ad spend is supporting your overall business — not just the slice of revenue Amazon's attribution model credits to ads.
The five most common causes: (1) bidding on overly broad keywords that attract irrelevant clicks, (2) missing negative keywords letting irrelevant searches drain budget, (3) poor listing conversion rate, (4) wrong match-type mix (too much broad match), and (5) campaign structure cannibalization where multiple campaigns bid against each other. The fastest fix for most accounts is mining the search term report for wasted spend and adding negatives.