Web attribution

Web attribution is the work of figuring out which ad, channel and touchpoint led to an order, a form submission or a phone call on a website. The data used for attribution includes link parameters (UTM, click IDs), the website’s own cookies and the events the website sends back to ad platforms.

What is web attribution?

A web attribution setup has four parts:

1. Tagging links: UTM parameters for Google Analytics, plus the click IDs that ad platforms add to links automatically when a user clicks.
2. Keeping the trail: cookies or browser storage hold that tag until the conversion happens.
3. Sending events: a pixel tag in the browser, or server-side events through the Conversions API.
4. Choosing the rules: the attribution model and attribution window decide which touchpoint gets the credit.

How well do cookies still work in 2026?

Safari blocks all third-party cookies by default. Cookies that JavaScript creates on the website itself are deleted after 7 days if the user doesn’t interact with the site. If a landing page receives a link with a click ID from a domain classified as capable of cross-site tracking, cookies set with JavaScript last only 24 hours (WebKit, Tracking Prevention in WebKit, accessed October 2026).

Chrome went a different way. On April 22, 2025, Google announced it would keep the current approach of letting users choose about third-party cookies in their settings, rather than rolling out a separate prompt as it had once planned (Google Privacy Sandbox, Next steps for Privacy Sandbox and tracking protections in Chrome, April 2025). On October 17, 2025, Google retired the Attribution Reporting API, Topics, Protected Audience and several other Privacy Sandbox APIs, while keeping CHIPS and FedCM (Google Privacy Sandbox, Update on plans for Privacy Sandbox technologies, October 2025).

In practice, Safari users and Chrome users from the same campaign leave different trails. Sending events from your server and using first-party data helps make up for what gets lost.

Attribution models and windows on Google and Meta

Google Ads uses data-driven as the default model for most conversion actions and still keeps last click. The first click, linear, time decay and position-based models have been removed, and conversions that used them were upgraded to data-driven (Google Ads Help, About attribution models, accessed October 2026). In GA4, those models were discontinued in November 2023.

Meta lets you choose between standard attribution and incremental attribution. Under standard attribution, website conversions are counted within 1 or 7 days after a link click, 1 day after a view, and 1 day after an engagement that is not a link click (Meta Business Help Center, About attribution models and attribution settings, accessed October 2026).

Example

Hypothetical: Lan clicks a fashion shop’s Meta ad on day 1. On day 3 she searches the shop’s name on Google, clicks a search ad and places a VND 850,000 order. Meta records 1 order because the shop set a 7-day click window. Google Ads records 1 order too. Add the two reports together and the shop sees 2 orders and VND 1.7 million in revenue, while the cash register only took in VND 850,000. GA4 with the data-driven model records just 1 order and splits the credit among the touchpoints.

Web attribution vs. mobile attribution

Frequently asked questions

Is UTM tagging alone enough?

UTM is enough for GA4 to know where a session came from. It doesn’t help Google Ads or Meta optimize bids, because those platforms need conversion events sent to them directly.

Should you change the attribution window to make the numbers look better?

A longer window raises the conversion count but doesn’t bring in a single extra customer. To find out how many orders your ads really add, you need incrementality testing.

If your website runs lead generation ads and the numbers don’t agree across platforms, see how Adtek handles it on our Lead Generation page.