Your HubSpot CMS site looks polished in the editor. Then you run it through PageSpeed Insights, and the mobile score comes back in the 50s. The culprit is almost never the platform itself. HubSpot ships with a global CDN, HTTP/2, and automatic minification. The performance gaps live in your templates, images, fonts, and accumulated scripts. HubBase has spent more than ten years diagnosing these exact problems on HubSpot CMS sites, and the fixes rarely require a full rebuild.
This guide walks you through seven targeted steps to diagnose and fix Core Web Vitals on your HubSpot site. Each step focuses on a specific metric and gives you a clear action plan your team can execute without tearing down what already works.
Before you change a single line of code, you need to know where each template stands. Open Google Search Console and navigate to the Core Web Vitals report. This report uses real visitor data from Chrome, which is what Google actually uses to evaluate your pages for ranking purposes.
Lab tools like Google Lighthouse give you a repeatable synthetic score. Field data tells you what your actual visitors experienced. You want both, but prioritize field data when deciding which template to fix first.
Record LCP, INP, and CLS separately for each page template. In HubSpot CMS, performance problems are almost always template-level. One slow blog post usually means every blog post is slow. Documenting per-template baselines lets you measure which fix moved the numbers after each change.
Run PageSpeed Insights on at least your homepage, a blog post, and a landing page. Note which metric fails on each. That prioritized list becomes your fix order for the steps that follow.
On most HubSpot pages, the Largest Contentful Paint element is the hero image. If that file is a 2 MB PNG exported at 3000 pixels wide, no other optimization will rescue the score.
Start by exporting the image at the widest size the layout actually uses. A hero section that renders at 1440 pixels wide does not need a 3000-pixel source file. Then convert to WebP format. According to Google's own documentation, WebP images average 26% smaller than equivalent PNGs with no visible quality loss.
Set explicit width and height attributes on every hero image. This single step prevents the browser from recalculating layout once the image loads, which also reduces CLS. Let HubSpot's built-in image resizing produce responsive variants rather than shipping one oversized file to every device.
Photographs belong in WebP or JPEG format. Reserve PNG strictly for flat graphics that require transparency. Run your top five landing pages through this process first, then move to blog templates and service pages.
Lazy loading below-the-fold images is a free performance win. Lazy loading the hero image, on the other hand, actively delays your LCP because the browser waits before requesting the one image the score depends on.
Many HubSpot themes apply lazy loading globally to all images. Check your hero module's code to confirm whether it uses loading="lazy". If it does, remove that attribute from the above-the-fold image and keep it on everything else.
The same logic applies to embedded video. Load a static poster image and fetch the video player only on user interaction rather than on page load. This approach keeps LCP fast while still giving visitors access to the video content when they want it.
Two font families with four weights each means eight files on the critical rendering path. Most sites use three of those weights. The rest add download time without adding anything to the design.
Start by auditing which font weights your stylesheets actually reference. Remove any that are declared but never used. Then self-host or preload the primary font file using a <link rel="preload"> tag so the browser starts downloading it early in the page load sequence.
Set font-display: swap on all font declarations. This tells the browser to render text immediately using a system fallback font, then swap in the custom font once it loads. Visitors see content faster, and your LCP improves because text does not stay invisible while fonts download.
Also check for icon fonts. Loading an entire icon font library to render four glyphs is an expensive trade-off. Replace icon fonts with inline SVG where possible. SVGs are smaller, render faster, and scale without quality loss.
Every HubSpot portal accumulates tracking scripts over time. A retired chat widget from a vendor you stopped using, an A/B testing tool from two campaigns ago, three overlapping analytics pixels that nobody can account for. They all execute on every single page view and cost real interaction time, dragging down your INP score.
Open your HubSpot portal settings and audit the site-wide header and footer HTML. List every third-party script and confirm that someone on your team still uses the data it collects. Remove anything nobody claims.
For scripts that remain, add async or defer attributes wherever the script is not needed during first render. This prevents those files from blocking the browser's main thread while your page content loads. According to the 2025 HTTP Archive Web Almanac, the median website loads 27 third-party scripts per page. Cutting that number by even a third can measurably reduce INP and improve overall responsiveness.
HubSpot themes carry CSS for every module they offer, including the ones your site never uses. Sites built by multiple contributors over time also accumulate near-duplicate modules with overlapping styles. The result is an inflated global stylesheet that slows rendering.
Identify which modules your pages actually use. Remove or deactivate the rest from your theme. Then look for modules that do the same job under different names and consolidate them into a single, well-maintained component.
Custom modules should scope their own CSS instead of appending to the global sheet. This prevents specificity conflicts that force developers to write increasingly aggressive override rules, adding even more CSS weight. HubBase builds HubSpot websites with modular, scoped CSS from day one so that stylesheet size stays honest as the site grows.
Cumulative Layout Shift on HubSpot pages usually traces back to three things: images without explicit dimensions, embedded forms that resize once their JavaScript loads, and cookie or promotional banners that push content down after the page renders.
For HubSpot forms, wrap the embed in a container with a min-height that matches the form's rendered height. This reserves space in the layout so surrounding content does not jump when the form script executes.
For banners and popups, overlay them on top of existing content instead of inserting them at the top of the document. Inserting a banner above your page content causes every element below it to shift downward, which is exactly what CLS measures.
Web fonts can also trigger layout shift when the fallback font's metrics differ significantly from the custom font. Choose a system fallback with similar proportions (for example, using a sans-serif system font as a fallback for a sans-serif custom font) to minimize the visible jump when the swap happens.
Google made Core Web Vitals a ranking factor in 2021. LCP measures loading speed, INP measures responsiveness to user input, and CLS measures visual stability. All three are evaluated at the 75th percentile of real user data from the Chrome User Experience Report.
The ranking impact is real but proportional. Google's John Mueller has described it as "more than a tie-breaker, but it also doesn't replace relevance." For HubSpot marketing teams competing in crowded search verticals, passing all three thresholds removes a penalty that competitors with faster sites do not face.
The indirect effects are often larger than the direct ranking signal. According to Yottaa's 2025 Web Performance Index, which analyzed over 500 million website visits, reducing page load time by just one second increased mobile conversions by 3%. Faster pages also reduce bounce rates. When visitors stay longer and convert at higher rates, engagement signals feed back into search rankings over time.
HubSpot injects its own tracking scripts, chat widget code, form JavaScript, and analytics bundles on every page. You cannot remove those platform-level scripts. That baseline overhead means your theme, images, fonts, and third-party scripts have less budget to work with before performance degrades.
The most common offenders on HubSpot CMS sites are oversized hero images (killing LCP), global lazy loading applied to above-the-fold content (also killing LCP), unused theme CSS from modules your site never uses (slowing render time), and accumulated third-party scripts from past campaigns (dragging down INP).
Template-level problems compound across your entire site. A single bloated blog template means every blog post inherits the same performance issues. Fixing the template once fixes every page that uses it, which is why auditing at the template level (step 1 above) gives you the highest return on effort.
HubBase brings hands-on experience in HubSpot website development and CMS migrations. This experience informs a diagnostic approach that focuses on identifying the specific performance bottlenecks affecting your HubSpot site, rather than relying on generic speed recommendations.
The HubBase team offers dedicated loading speed optimization that covers image compression, JavaScript and CSS delivery optimization, font trimming, redirect reduction, and ongoing performance monitoring. Every fix targets a measurable Core Web Vital metric so you can track improvement in real field data.
For teams that need ongoing support rather than a one-time fix, HubBase's Website Growth Retainer provides 10 flexible hours each month. Those hours can go toward Core Web Vitals fixes, conversion rate optimization, SEO improvements, or new landing page builds, whichever is highest priority that month.
If your templates are too tangled to fix incrementally, a clean rebuild on properly scoped templates is often faster than untangling years of accumulated technical debt. HubBase's development process prioritizes loading speed and security from the first line of code.
Core Web Vitals are three performance metrics defined by Google that measure loading speed (LCP), responsiveness (INP), and visual stability (CLS). Google uses these metrics as ranking factors, evaluated using real visitor data from Chrome browsers. HubBase optimizes all three metrics as part of its speed optimization service.
Yes. Most Core Web Vitals issues on HubSpot CMS stem from image sizes, font loading, unused scripts, and CSS bloat. Fixing these at the template level improves every page that uses that template. HubBase regularly resolves failing Core Web Vitals scores through targeted template-level fixes rather than full redesigns.
LCP is the most common failure point because HubSpot pages frequently feature large hero images that are not compressed or converted to modern formats. Fixing the hero image alone often moves LCP from "poor" to "good" within a single deployment.
Lab tool improvements (like PageSpeed Insights scores) appear immediately after deployment. Field data in Google Search Console typically takes 28 days to reflect changes because Google collects data over a rolling window. HubBase recommends retesting in both environments to confirm each fix delivered the expected improvement.
HubSpot's CDN handles geographic content distribution, HTTP/2, and automatic minification. These features provide a solid performance baseline. The remaining Core Web Vitals work falls on your templates, assets, and third-party code. HubBase builds on top of HubSpot's infrastructure to close those remaining gaps.
Use Google Search Console for field data (real visitor metrics) and Google Lighthouse or PageSpeed Insights for lab data (synthetic testing). Run both before and after each fix to measure progress. For ongoing monitoring, HubBase includes regular performance audits as part of its website support plans.