Amazon vs Shopify: what you can and cannot measure

Amazon Attribution credits Amazon sales to a tagged, non-Amazon click inside a 14-day last-touch window and reports them in aggregate, while a Shopify store gives you each order under credit rules of its own. The two ROAS figures describe different windows, different rules and different products, and neither says what would have sold without the ad. Line them up on the same dates and compare margin per order before you move budget.

What does Amazon let a brand measure?

Amazon Attribution is free. Amazon's page says it is for professional sellers enrolled in Brand Registry, vendors, KDP authors and agencies. You place an attribution tag in the final destination URL of a non-Amazon ad, and Amazon reports what happens on Amazon after the click: clicks, detail page views, add-to-carts, purchases, units sold, product sales and new-to-brand purchases. Its guide says a click earns credit only if the conversion happens within 14 days of it, and the most recent click takes the credit.

Brand Analytics is a separate Seller Central tool for brand-registered sellers with a Professional account. Amazon describes it as a tool "that brands can use to review aggregate customer data". Its Demographics dashboard "breaks down sales by customer age, income, education, gender, and marital status", and its Repeat Purchase Behavior dashboard tracks orders, repeat sales and the number of repeat customers.

Amazon's own pages differ on availability: the product page lists the Netherlands among its marketplaces, and the guide's list of seven countries doesn't. The guide shows no date and still calls Attribution a beta, so prefer the product page where they differ, and check your marketplace in your Amazon Ads account before you plan around it.

What does a Shopify store let you measure?

Shopify's marketing reports summarize "all Online Store channel orders", so sales made on Amazon aren't in them. Its Sales attributed to marketing report counts sales from campaigns made in Shopify's Marketing section and from links that carry UTM parameters, and the reports let you switch between five models. Marketing activity reports credit the ad clicked most recently within the past 30 days. GA4 adds a third rule set: three attribution models, all of which "exclude direct visits from receiving attribution credit, unless the path to key event consists entirely of direct visits".

For the processing it covers, Shopify's data processing addendum says "You shall act as a Data Controller and Shopify shall act as a Data Processor" for your customers' personal data. It also has you warrant that you give your customers the ability to exercise data rights requests.

Why can't you compare the two ROAS figures?

Three differences show up in Amazon's and Shopify's own documentation:

1. Different clocks. Amazon's window is 14 days from the click. Shopify's marketing activity reports look back 30 days. For illustration: a click followed by a purchase 20 days later is inside Shopify's window and outside Amazon's.
2. Different products. Amazon's total product sales include products from the same brand as the promoted ones, the brand halo. Shopify counts the store's own orders.
3. Different economics. Amazon's guide says US seller brand owners in its Brand Referral Bonus program earn a bonus averaging 10% of product sales driven by non-Amazon marketing that Attribution tracks. Nothing in the Shopify reports cited here matches it.

What evidence is there that optimizing with Attribution pays off? The only quantified result Amazon's guide prints is an average 18% increase in new-to-brand sales for advertisers that optimized with Attribution insights, from Amazon's own study across 93 advertisers between November 2020 and April 2021. That is published by Amazon, not independently audited, and the page doesn't say what the increase is measured against. This page cites no independent measurement of Amazon Attribution.

What can you check for free this week?

Run this for one campaign and one date range:

1. Pull three exports. The Amazon Attribution report for the campaign's tag, Shopify's Sales attributed to marketing report for the same utm_campaign, and the ad platform's click and spend figures.
2. Label each line. Write the window and credit rule beside every sales figure: Amazon's last-touch window, and Shopify's last-click window or its last non-direct click default. Keep Amazon's promoted-product sales and its total with brand halo on separate lines.
3. Work out margin per order on each side. Use each channel's own costs, and include Amazon's bonus only if you are enrolled.
4. Rank by margin, then by ROAS. For illustration: with EUR 400 of spend per destination, Amazon credits EUR 1,600 of sales (ROAS 4.0) at a 25% margin, which leaves EUR 1,600 x 0.25 - 400 = EUR 0, while the store credits EUR 1,200 (ROAS 3.0) at a 45% margin, which leaves EUR 1,200 x 0.45 - 400 = EUR 140.

Pass: both rankings agree, and every sales line names its window and rule. Fail: the destination with the higher ROAS has the lower margin per order, which means the ROAS ranking would have moved budget the wrong way. Both tools credit clicks, and credit isn't lift: to learn what the ad added, run a holdout.

Sources, 30 September 2026: Amazon Attribution: Get started with advertising analytics (Amazon Ads, page read 30 September 2026); Marketing reports (Shopify, page read 30 September 2026); Your complete guide to Amazon Attribution (Amazon Ads, page read 30 September 2026); Get started with attribution (Google, page read 30 September 2026); Amazon Brand Analytics (Amazon, page read 30 September 2026); Measuring marketing performance (Shopify, page read 30 September 2026); Shopify Data Processing Addendum (Shopify, page read 30 September 2026)

Related answers

• Selling on Amazon and Shopify: keep the channel data apart
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• Marketing ROI for ecommerce: profit per order, not clicks
• Incrementality testing
• Contribution margin calculator