18.26% increase in Google Ads conversions with Click ID cookies using server-side tracking | Lars Friis

Lars Friis, a Danish tracking expert and our longstanding partner, recently set out to measure how many extra Google Ads conversions with click ID cookies could be captured after switching from client-side to server-side tracking. He set up the server-side configuration for his clients, monitored their performance, analyzed the resulting data, and shared the test outcomes with us.

Safari ITP limits cookie lifetime to 24 hours, which means Google Ads click ID cookies can expire before a user completes a purchase. This short lifespan causes gaps in attribution and weakens the data passed back to Google Ads:

• Conversions that happen after 24 hours are recorded without a click ID.
• Google Ads reports fewer conversions than it should.
• Automated bidding receives weaker signals and may optimize poorly.
• Longer purchase cycles lose the largest share of reported conversions.

To address these tracking challenges, Lars implemented a server-side tracking setup using Stape. The goal was to bypass the 24-hour limitation and make sure Google Ads cookies "survive" for the entire duration of the conversion window (e.g., 30 days).

A core component of the configuration was the same origin custom domain. It runs the server-side endpoint on a domain that matches the website (e.g., example.com/sgtm), which allows setting first-party cookies and lengthens their lifespan.

Lars monitored his clients' tracking implementations to perform comparisons between client-side and server-side Google Ads performance.

In Google Ads, there are the following cookies:

These cookies contain a timestamp from when they were set. For example:

GCL.1769589044.Cj0KCQiAhOfLBhCCARIsAJPiopPyVORTLBy1Brv54mqlWDz2fxksnUMKFxMX_wJgh08rLbW80Muj4QQaAkthEALw_wcB

In this data string, our time stamp is 1769589044.

To identify "recovered" conversions and verify the uplift, Lars analyzed the data based on two criteria:

1. 1.
   Was there a cookie containing a valid click ID?
2. 2.
   Was that click ID timestamp within the designated conversion window (e.g., 30 days)?

This comparison allowed him to quantify how many sessions and conversions would be captured exclusively through server-side persistence versus those identifiable via client-side cookies. For example, if the client-side cookie was missing (i.e., deleted by Safari) but the server-side cookie remained, the conversion was attributed strictly to the server-side setup.

One of Lars's eCommerce clients revealed the following results:

• Conversions with client-side cookies: 7,466.
• Conversions with server-side cookies: 8,841.
• Server-side uplift: 1,365, i.e., (8,841 - 7,466).

These 1,365 conversions represent the pure value added by the server-side implementation. In other words, these are the sales that would have gone unreported, given client-side cookie limitations. Therefore, the conversion uplift attributable to server-side tracking is:

This means that for every 100 conversions tracked under the legacy setup, nearly 19 more were recovered and attributed correctly with the server-side approach.

Across other clients, Lars observed conversion uplifts typically ranging between 5% and 20%, depending on the length of the purchase journey.

By setting up server-side tracking with Stape, you can:

• Bypass ITP restrictions: extend cookie lifespans beyond the 24-hour limit imposed by Safari, capturing attribution for purchase journeys that take days or weeks.
• Use a same origin domain setup: run your server-side endpoint on a domain that matches your website to set first-party cookies and lengthen their lifespan, resulting in more stable attribution and fewer lost click IDs.
• Recover lost conversions: feed Google Ads automated bidding strategies with more complete data, allowing for better optimization and a clear view of true conversion uplift.