Are Core Web Vitals affected by Google Ads?

Summary: Our data shows that the question should actually be: by how much? And a bad Time to First Byte will even impact both user engagement and Core Web Vitals, via the First Contentful Paint and Largest Contentful Paint metrics. This happens because Google Ads will add a redirect for tracking purposes once a user clicks. Add inefficient caching rules on top of this, and you've got yourselves expensive traffic that is less likely to convert.

  • by Roderik Derksen
  • Published
  • Reading time ± 4 minutes
  • SEA Google Ads
Are Core Web Vitals affected by Google Ads?

Why Lighthouse isn't telling you this

Instead of synthetic testing, such as Lighthouse does, RUMvision tracks the experiences of your very own audience. In other words: real user.

And did you know Lighthouse won't even track your Time to First Byte and anything that impacted the TTFB metric? So, when using Lighthouse, you will never learn about the impact of your Google Ads on your users' experiences.

And that's a shame, as many merchants still are using Lighthouse as their Single Source of (performance) Truth. A missed opportunity, but also an expensive one as it fully blinds them to what might be impacting their Core Web Vitals and conversion for a while already.

How RUMvision is doing it differently

That's the first important nuance: RUMvision has been designed with minimal configuration in mind to make it equally easy to get started as Lighthouse. But it's also showing you the experiences of all users. And their conditions, such as internet speed, and device memory. And today's topic: ads, campaigns, and the query strings that are involved with them. Even those your business wasn't aware of.

Lots of Google Ads traffic

Since many eCommerce websites rely on Google Ads, this means that -in terms of page speed- you need to manage this well in terms of expectations. With a lot of Google Ads traffic, there is a limit to what you can do to optimize the TTFB, and thus overall site speed.

A webshop without Google Ads has a faster TTFB, which results in a better fundament for the First Contentful Paint (FCP) and the Largest Contentful Paint (LCP). Or in other words: visual loading experiences and thus early user engagement.

In what situations can Google Ads hurt passing Core Web Vitals?

Google Ads traffic also contributes to the Core Web Vitals rating. After all, all Google Chrome visitors are included in the rating. We've seen eCommerce sites that rely on Google Ads for 80%. So, 80% of their traffic is reaching their site through an ad click, resulting in a slower TTFB.

Core Web Vitals percentile

Google is looking at the 75th percentile for each metric. In other words, Google wants you to be able to deliver an optimal experience across all Core Web Vitals metrics for at least 75% of your Google Chrome pageviews. When 80% of your traffic comes from Google Ads, and their first experience is below-par, then:

  • it will impact UX / user engagement, bounce, and thus conversion;
  • and at the same time has a high risk of impacting your Core Web Vitals and thus SEO.

First situation

In our audits and monitoring solution, we see that about half of the webshops do not have their caching strategy set up properly. This means that visitors who come in with a ?gclid query have a TTFB that is 3 to 8 times worse than a visitor without this query.

The screenshot below from a real-world webshop with quite some visitors per group is perfectly able to illustrate this.

Core web vitals google ads

You might have forgotten to add a certain query string to the caching strategy. For example, if you're using a Content Delivery Network (CDN) such as Cloudflare. As shown above, this quite is a small or big page speed issue, also depending on the platform you're using. And it only takes 5 minutes to fix this.

Second situation

The often-overlooked waiting time is one of them. As you can see in the image below, the waiting time for a query string goes up considerably. Instead of contributing to your TTFB by only 17%, it increases to 51%. In this case, it resulted in a massively regressed TTFB.

This happens because the request goes through a (tracking) redirect to the destination page. Unfortunately, you cannot change this yourself. So if you depend on a lot of Google ads traffic then you have to adjust your business expectation regarding TTFB.

waiting time google ads

Enable parallel tracking

If you're making use of Google Ads check if parallel tracking is enabled. By enabling this your ad landing pages TTFB (and also FCP and LCP) will improve. It also might help you to increase your Ad Campaign Performance, just like Vodafone.

How does parallel tracking work?

Parallel tracking Google Ads

With parallel tracking, customers go straight to your landing page while click measurement happens in the background.

Here's an example of parallel tracking:

  1. Client clicks on your ad.
  2. Your landing page is seen by your customer.

In the background, at the same time:

  1. The click tracker for Google Ads loads.
  2. Monitoring URL loads.
  3. If you use more than one click tracker, you may have to load more redirects.

Without parallel tracking, when a customer clicks on your ad, they may have to go through one or more redirects before they get to your landing page. This means that customers will take longer to get to your landing page.

Without parallel tracking, tracking looks like this:

  1. Client clicks on your ad.
  2. The click tracker for Google Ads loads.
  3. Monitoring URL loads.
  4. There's a chance that an extra tracking URL loads.
  5. Your landing page is seen by your customer.

Source: Google Support

Benefits of Core Web Vitals on Google Ads

Good Core Web Vitals contributes to better PPC results. In Google Ads, the quality score (experience on the landing page) can contribute to your position and thus directly affects the bid to achieve a certain position. We have seen, in real-life cases, that improving the technical experience has led to a reduction in CPC of up to 20-25%. You could also consider the fact that better page speed benefits the automated bidding strategy as a nice bonus.


We know we can only address Google Ads TTFB issues to a certain degree. Webshops with performance in their DNA are very likely to make up for bad TTFB experiences. If your company isn't there yet, it might be good to know about any benefits too:

  • help other stakeholders to understand the drawbacks of Google Ads;
  • and help initiate page speed conversations.

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