Advertising cost of sales (ACOS) is the share of attributed revenue that was spent on advertising to get it. Amazon Ads defines it as ad spend divided by ad revenue, multiplied by 100: a campaign that costs 50 dollars and is credited with 100 dollars of sales has an ACOS of 50%. The metric exists because Amazon's sponsored ads are bought by merchants who think in margins rather than media ratios. A seller can read an ACOS figure directly against a margin. It is the same arithmetic as return on ad spend (ROAS), turned upside down.

How the number is built

Amazon's own guide gives the two formulas side by side: ACOS equals ad spend divided by ad revenue, times 100; ROAS equals ad revenue divided by ad spend. In Amazon's example, the 50% ACOS corresponds to a ROAS of 2. A 25% ACOS is a ROAS of 4, and a 10% ACOS is a ROAS of 10.

The numerator is what Amazon charged for clicks, or for impressions in campaigns billed on viewable cost per thousand impressions (vCPM). Three settings decide the denominator.

The first is the ad type. ACOS is reported for Sponsored Products, the cost-per-click listings that appear in search results and on product pages, and for Sponsored Brands and Sponsored Display (which Amazon now groups under display ads). Marketers judge Sponsored Products on ACoS, ad spend divided by attributed revenue, more than on any other figure.

The second is the attribution window. According to Openbridge's documentation of Amazon's reporting, the advertising console credits Sponsored Products sales to a click within 7 days for sellers and within 14 days for vendors, the brands that sell wholesale to Amazon. Sponsored Brands and Sponsored Display use 14 days. The Amazon Ads application programming interface (API) also exposes 1, 7, 14 and 30-day versions. The same campaign can show two ACOS figures depending on which column a tool pulls.

The third is which products count. Attributed sales are not limited to the item in the ad. API field lists published by reporting vendors separate total attributed sales from "promoted product sales attributed to ad clicks", and m19's Tarik Berrada Hmima wrote in February 2022 that "sponsored sales attribution can come from different ASINs", the Amazon Standard Identification Numbers that label each product. A shopper who clicks an ad for one charger and buys a cable from the same brand can lower the charger campaign's ACOS.

A worked example

A seller lists a 40 dollar product. After the cost of goods, Amazon's referral and fulfilment fees, the seller keeps 12 dollars per unit, a 30% margin before advertising. Amazon's guide calls this the break-even ACOS: "In order to maintain a profit, your Amazon ACOS needs to be lower than your profit margin."

Over a month, a Sponsored Products campaign spends 1,200 dollars and is credited with 4,800 dollars of sales, or 120 units. ACOS is 25% and ROAS is 4. The campaign's attributed units generate 1,440 dollars of margin against 1,200 dollars of spend, a profit of 240 dollars. At a 20% margin, the same campaign would lose 240 dollars, though its ACOS would not change.

ACOS also decomposes into three inputs that move independently: cost per click divided by the product of conversion rate and average order value. With a 1 dollar click, a 10% conversion rate and a 40 dollar order, ACOS is 25%. Double the click price and ACOS doubles to 50% with no change in the product or the shopper.

Who sets the target, and how

Neither Amazon's dynamic bidding nor its fixed bids take an ACOS figure as an input. Amazon's three standard Sponsored Products strategies are dynamic bids down only, dynamic bids up and down, and fixed bids, with placement adjustments of up to 900% for top of search and product pages, according to PPC Land's Sponsored Products explainer. Amazon's own target-based tools are framed in ROAS. Rule-based bidding, described by the agency JumpFly in July 2022 as the newest strategy, uses a ROAS guardrail and requires 30 days of history and 30 conversions. A beta labelled "Automatically optimizing ROAS within budget" for select US Sponsored Products accounts, reported by Novadata in February 2026, replaces the bid entirely.

The target ACOS therefore lives mostly outside Amazon's interface: in seller spreadsheets, agency rules and third-party bid management software that reads Amazon's API and adjusts bids to hold a percentage. That ecosystem grew early. Merkle said in December 2018 that clients moving Sponsored Brands bidding onto its tool saw a 62% decrease in ACoS, and Feedvisor reported a 46% decrease a month later. Both were unverified company claims.

Origin and evolution

Seller Labs called ACoS "an Amazon-invented metric" in 2021. Most trade histories date Amazon's self-serve cost-per-click business to Amazon Marketing Services (AMS) in 2012, though accounts vary. In September 2018, AMS, the Amazon Advertising Platform and Amazon Media Group were folded into Amazon Advertising, and Headline Search Ads became Sponsored Brands. The Amazon Ads name followed in 2021.

The spelling has never been fixed. Amazon's console and guides write "ACOS" and "advertising cost of sales"; Seller Labs and much of the agency trade write "ACoS" and "advertising cost of a sale". In Amazon's Profit Analytics dashboard, released on September 18, 2025, a tile labelled "Advertising Cost of Sales" showed a dollar total, not a percentage.

The reporting definitions have moved underneath the label. According to Supermetrics, Amazon added 14-day ACOS and ROAS fields to Sponsored Display reporting in January 2024 and stopped returning the 1, 7 and 30-day versions after October 31, 2024. On January 1, 2026, Amazon applied shopping-signal enhanced attribution to view-tracked Sponsored Brands, vCPM Sponsored Display and some Amazon DSP campaigns, with shorter windows, and kept the old 14-day method under a separate "Purchases (all views)" family.

Why it matters to marketers

In seller forums, agency case studies and software dashboards, ACOS is the default unit of success on Amazon. When Amazon introduced its hourly data feed, Amazon Marketing Stream, PPC Land's coverage carried a partner case study claiming an 85% decrease in ACOS for a UK brand. When Amazon moved Reach and Page Visit campaigns in Sponsored Display to conversion optimisation in April 2025, it described the change as prioritising ROAS and ACOS.

For advertisers working across Google, Meta and retail media, the inversion is a translation cost: IAB Europe's retail media measurement standards of April 2024 define ROAS and recommend a 30-day click and view window, and do not mention ACOS.

Limitations and disputes

ACOS measures attributed sales, not caused sales. A shopper who searches for a brand by name and clicks its sponsored listing would often have bought anyway, so branded campaigns tend to show low ACOS without creating much demand. Separating the two requires an experiment, the subject of incremental ROAS.

It ignores what happens off the ad. Sponsored Products placements can lift organic ranking by generating sales velocity, which ACOS does not credit, and a low ACOS can coexist with shrinking total sales. That gap gave rise to TACoS, discussed below.

It is not a profit measure. The worked example above shows identical ACOS producing a profit at one margin and a loss at another. Amazon's holiday "Ads Math" guide uses break-even ROAS instead: one divided by gross margin.

Its value depends on prices nobody outside Amazon could see. On August 31, 2026, the Federal Trade Commission and 22 states sued Amazon over about 20 billion dollars in alleged hidden ad surcharges, alleging a "soft reserve" applied after a nominal second-price auction. The complaint says the share of clicks charged the advertiser's full bid rose from about 4% in late 2020 to 79.1% in 2024. Amazon denies overcharging and says average cost per click stayed flat in real terms from 2019 to 2024.

Not the same as

ROAS is the same calculation inverted; neither contains more information.

TACoS, or total advertising cost of sale, divides ad spend by all sales, including organic ones. Amazon does not document it in the guides reviewed for this article. Agencies and software vendors use it to judge whether advertising grows the business or buys sales that search would have delivered.

Cost of sales in accounting means the cost of goods sold, the direct cost of producing what was sold.

Cost per acquisition (CPA) divides spend by conversions rather than by revenue. It treats a 10 dollar order and a 100 dollar order alike, which ACOS does not.

Recent developments

Amazon has been nudging its reporting towards ROAS. Early in 2026, an account named Indy_Amazon told a seller on Amazon's Seller Central forums who could no longer find ACOS in campaign views that "ACOS is still available" through the Customize columns menu, adding that Amazon had been moving advertising reporting towards ROAS. Unified reporting, which reached general availability on June 8, 2026, standardised metrics and moved attribution from a conversion-based to a traffic-based method; Amazon will retire the legacy Sponsored Ads reports page on December 31, 2026.

On September 29, 2026, Amazon relaunched Ads Agent as the front door to a merged interface and renamed its DSP buying product DVA. Amazon's performance claims for DVA+ were stated in cost per acquisition and ROAS. On October 15, 2026, an Amazon Ad Lab video comparing fixed and dynamic bidding still told advertisers to watch four metrics including ACOS and ROAS, without publishing results. Pacvue's Q3 2026 benchmark report put Sponsored Products cost per click down 3% year on year and Sponsored Brands up 13%, movements that pass straight into ACOS.

Timeline

  • 2012 - Most trade histories date Amazon Marketing Services' self-serve cost-per-click sponsored ads to this year; accounts vary.
  • September 2018 - AMS, the Amazon Advertising Platform and Amazon Media Group merge into Amazon Advertising; Headline Search Ads become Sponsored Brands.
  • December 19, 2018 - Merkle launches automated bidding for Sponsored Brands, citing a 62% ACoS decrease for clients.
  • 2021 - Amazon Advertising becomes Amazon Ads.
  • July 2022 - Rule-based bidding with a ROAS guardrail is described as Amazon's newest Sponsored Products strategy.
  • January 2024 - 14-day ACOS and ROAS fields added to Sponsored Display reporting, according to Supermetrics.
  • April 2024 - IAB Europe's retail media measurement standards define ROAS, not ACOS.
  • October 31, 2024 - 1, 7 and 30-day Sponsored Display ACOS and ROAS fields stop returning data.
  • April 4, 2025 - Sponsored Display Reach and Page Visit campaigns move to conversion optimisation.
  • September 18, 2025 - Amazon releases the Profit Analytics dashboard for sellers.
  • January 1, 2026 - Shopping-signal enhanced attribution applied to view-tracked campaigns; legacy "all views" metrics retained.
  • February 2026 - ROAS auto-bidding beta reported for select US Sponsored Products accounts.
  • June 8, 2026 - Unified reporting reaches general availability.
  • August 31, 2026 - FTC and 22 states sue Amazon over alleged hidden ad surcharges.
  • September 29, 2026 - Ads Agent relaunched over a merged interface; Amazon DSP renamed DVA.
  • October 15, 2026 - Amazon Ad Lab video recommends ACOS among four bidding metrics.
  • December 31, 2026 - Legacy Sponsored Ads reports page scheduled for retirement.

Summary

Who: Amazon Ads, which defines and reports the metric; sellers, vendors and agencies that set ACOS targets; third-party bid management and reporting vendors that build on Amazon's API; and regulators, including the FTC, whose complaint concerns the click prices that feed it.

What: Ad spend divided by attributed ad sales, expressed as a percentage. It is the inverse of ROAS, and its value depends on the ad type, the attribution window (7 or 14 days for clicks in the console) and whether sales of products other than the one advertised are counted.

When: It arrived with Amazon's self-serve sponsored ads, usually dated to 2012, and became the trade's default efficiency measure for Amazon. Since 2022 Amazon's own target tools have been framed in ROAS, and in 2026 attribution and reporting changes altered how the denominator is counted.

Where: In the Amazon Ads console and API reports for Sponsored Products, Sponsored Brands and Sponsored Display, in third-party bidding software, and in agency and seller reporting. It is rarely used outside Amazon.

Why: It lets merchants compare advertising cost directly with product margin. Because it counts attributed rather than incremental sales, ignores organic effects and depends on auction prices that Amazon controls, a low ACOS is not proof of a profitable or growing business.