Gtag.js increasing LCP in pagespeed insights

Question

I have a problem with lcp score in core web vitals (mobile). My LCP score is 3 seconds. The required lcp score is 2.5 seconds in mobile. I have tried everything. Have optimized images with a premium plugin (EWWWW Image Optimizer). Serving the files through a CDN. Reduced the network requests to a minimum and applied other things which are common. The only way I can get the lcp score down is by removing gtag.js. This reduces the lcp to 2 seconds but I really need this script for analyzing the traffic. Is there any other way I can reduce the LCP? HAve tried all the suggestions listed in Lighthouse. Removed Unused CSS,JS. Defered Loading of Images, CSS, JS.

Answer 1

The PageSpeed Insights results that stand out to me are:

• Avoid an excessive DOM size (1,889 elements)
• Minimize main-thread work (3.5 s)

In the mobile test, PSI reports 3.5 seconds spent on the main thread, with 1.275 s on style and layout. I think some of this can be attributed to the large DOM. So try to find ways to trim excess content or markup from the page to simplify the HTML structure.

Script evaluation also accounts for 0.987 s, suggesting that there is significant JavaScript code that runs on page load. I'm not too familiar with GTM but based on the results it does seem like it's contributing a lot to main thread consumption (2.88 s). Some things to check are disabling or removing unnecessary services in GTM, as these third parties can be adding excess JavaScript, and optimizing the services you do need so that anything not absolutely necessary for the initial page load is deferred until later. See the Loading Third-Party JavaScript guide for some additional advice related to GTM.

Answer 2

On the live site, the slider image is the LCP, and this is loaded via CSS. The browser does not know to load the image until the CSS is loaded and it knows the image is needed on the page. You could speed things up with a preload on that image.

You're also using a lot of web fonts. You would free up bandwidth for the main image by reducing the number of fonts.