Top UI/UX Mistakes That Hurt Your Core Web Vitals Scores

Improving website speed, stability, and responsiveness is essential for delivering a strong user experience, and understanding the top UI/UX mistakes that hurt your Core Web Vitals is the first step. These Vitals measure how fast your content loads, how visually stable your layout is, and how quickly users can interact with your interface.

While many think performance issues come from hosting or servers, the truth is that most problems stem from UI/UX choices: oversized hero images, intrusive pop-ups, heavy scripts, and poorly structured layouts. These design decisions directly impact LCP, CLS, and INP, often without designers realizing it.

This guide breaks down the most common UI/UX mistakes affecting Core Web Vitals, and shows you how to fix them without sacrificing visual appeal.

What Are Core Web Vitals? (Quick Overview)

Core Web Vitals are a set of performance metrics defined by Google to measure how real users experience your website. They focus on three critical aspects of performance: loading, visual stability, and responsiveness, all of which directly influence how quickly a page becomes usable. As of 2025, Google evaluates three primary Core Web Vitals:

1. Largest Contentful Paint (LCP)

LCP tracks how long it takes for the largest visible element in the viewport to load. This is usually a hero image, title, banner, or large block of text.

A “good” LCP score is 2.5 seconds or faster.

A slow LCP often signals heavy images, slow servers, render-blocking resources, or poor media optimization. Improving LCP helps users see meaningful content sooner, lowering bounce rates and improving perceived performance.

2. Cumulative Layout Shift (CLS)

CLS measures how much layout movement occurs while the page is loading.

A CLS score of 0.1 or lower is considered good.

High Cumulative Layout Shift usually comes from UI elements shifting around due to images without set dimensions, late-loading ads, dynamic pop-ups, or fonts rendering late. A stable layout helps users interact confidently without unexpected jumps or accidental clicks.

3. Interaction to Next Paint (INP)

INP replaced the older FID metric because it evaluates all interactions throughout a user’s session, not just the first one.

A good INP score is 200 ms or less.

Interaction to Next Paint measures how quickly your site responds when users click, tap, or type. Slow interaction is usually caused by heavy JavaScript, long-running tasks, animations, or excessive UI complexity. A low INP score ensures the interface feels smooth and responsive.

UX Psychology Laws That Influence Performance

UX decisions are closely tied to how users think, react, and interact with a website. When design ignores basic psychology principles, it often leads to cluttered interfaces, delayed interactions, and unstable layouts that negatively impact Core Web Vitals.

• Hick’s Law: Too many choices slow user decision-making and often result in cluttered layouts, large menus, and unnecessary UI elements. This increases DOM size and resource loading, which can negatively affect LCP and overall page speed.
• Fitts’ Law: Small or poorly positioned buttons increase interaction effort, especially on mobile devices. When users struggle to tap or click elements, interaction delays rise, directly impacting INP and perceived responsiveness.
• Jakob’s Law: Users expect familiar navigation and interaction patterns. Unconventional UI designs create hesitation and repeated interactions, often requiring heavier JavaScript, which can slow input response and worsen INP.
• Gestalt Principles: Poor visual grouping, spacing, and alignment make layout shifts more noticeable. When elements load inconsistently, users perceive instability, increasing CLS and reducing layout trust.

Following these UX laws simplifies interfaces, reduces complexity, and directly supports stronger Core Web Vitals performance.

How UI/UX Mistakes Impact Core Web Vitals?

While CWV metrics are technical, the root cause of poor performance often lies in design choices. Unstable layouts, heavy images, and high request counts usually contribute to slow LCP and poor CLS across many websites.

UI/UX decisions directly influence CWV because:

• Heavy hero banners slow down LCP.
• Elements that shift during loading worsen CLS.
• JavaScript-heavy interactions worsen INP.
• Unresponsive mobile layouts delay loading and increase interaction delays.

This means design and performance are inseparable; your UI/UX decisions directly shape the user experience and your Core Web Vitals scores.

What Are the Basics of UI/UX Design?

Before reviewing the common UI/UX performance issues, it’s important to understand the fundamentals that guide effective and user-friendly design. These principles shape how users perceive, interact with, and navigate your website.

Visual Hierarchy

A clear visual hierarchy helps users instantly understand what’s important on a page. Proper spacing, contrast, and typography guide their attention and make content easier to scan and interact with.

Consistency

Consistent layouts, fonts, colors, and interaction delay patterns create familiarity. When users know what to expect, they navigate faster and experience fewer frustrations, improving overall usability and engagement.

Minimalism

Minimalism eliminates clutter by keeping only essential elements on a page. Reducing unnecessary visuals or components speeds up loading, improves clarity, and supports better performance and decision-making.

Responsive Design

Responsive design ensures your layout adapts fluidly to different screen sizes. A responsive site maintains usability across devices, prevents layout issues, and reduces reflow or resizing problems that affect performance.

Accessibility

Accessible design prioritizes readability, contrast, proper text size, and intuitive interaction. It helps all users, including those with disabilities, navigate comfortably, improving usability and compliance with web standards.

Performance-Aware Design

Performance-aware design focuses on choosing optimized images, efficient fonts, streamlined scripts, and lightweight components. It ensures the visual appeal doesn’t slow down the website or negatively affect Core Web Vitals.

Common UI/UX Issues That Affect Core Web Vitals

Below are the most common UI/UX performance issues that directly impact LCP, CLS, and INP, and ultimately harm user experience.

Slow-Loading Pages

Large hero sections, HD images, autoplay videos, heavy sliders, and oversized backgrounds often delay LCP.

Common causes include:

• Uncompressed media
• CSS/JS blocking rendering
• Large above-the-fold images
• Using outdated image formats instead of modern alternatives like WebP

Slow-loading pages negatively affect user satisfaction and Core Web Vitals.

Layout Shifts Caused by Poor Element Placement

Unexpected layout shifts, ads loading late, images without set dimensions, and dynamic banners contribute to a bad CLS score.

Examples of design choices that cause shifts:

• Images or iframes without width and height attributes
• Buttons that move when fonts load
• Late-loading pop-up banners
• Auto-inserted widgets or dynamic content without placeholders

Even small UI/UX performance issues in spacing or dynamic elements can destabilize the layout significantly.

Too Many Pop-Ups and Intrusive UI Patterns

Pop-ups, sticky bars, chat widgets, and notification prompts often load late or overlay content unexpectedly.

They affect Core Web Vitals by:

• Causing layout movements (hurting CLS)
• Blocking interactivity (hurting INP)
• Increasing JavaScript execution (slowing responsiveness)

Intrusive UI patterns also frustrate users and increase bounce rates.

Unoptimized Heavy Images, Icons, and Media

As images usually take up the most space on a webpage, slowing down the LCP significantly.

Common UI/UX mistakes include:

• Uploading images larger than necessary
• Using multiple decorative images instead of CSS or SVG
• Not using responsive image sizes (srcset)
• Using icon sets instead of lightweight SVG icons
• Auto-playing or high-FPS animations

Unoptimized media also increases data transfer, slowing mobile performance.

Overcomplicated Navigation and Menus

Mega menus, multi-level navigation, heavy dropdown animations, and script-dependent menus all degrade INP and even LCP.

Complex navigation can:

• Require excessive JavaScript
• Load large resources before interaction
• Slow down the first meaningful paint
• Create delays when users tap menu items on mobile

Simplified navigation supports both usability and performance.

Non-Responsive or Poor Mobile Layouts

A non-responsive layout forces the browser to zoom, resize, and realign content, which increases layout calculations and lowers performance.

Common issues:

• Too many columns on mobile
• Fixed-width containers
• Small touch targets
• Fonts that reflow when resized
• Images not scaling properly

Since mobile traffic dominates, poor mobile UX heavily impacts Core Web Vitals.

Excessive JavaScript Interactions Slowing Input Response

INP measures how fast your site responds to interactions, and too much JavaScript is the biggest reason for delays.

Examples:

• Heavy animation libraries
• Slider/carousel scripts
• Large JS frameworks for simple interactions
• Non-essential features blocking the main thread

When the browser is busy processing tasks, user interactions lag.

Fonts and Typography Causing Delayed Rendering

Fonts affect both layout stability and render time. Improper font loading can cause FOIT (flash of invisible text) or FOUT (flash of unstyled text), contributing to CLS. Optimizing typography is key to improving Core Web Vitals.

Common font-related UI/UX mistakes:

• Using many font families or weights
• Not preloading important fonts
• Using font files larger than necessary
• Not using font-display: swap
• Depending on external font providers that load slowly

How to Fix These UI/UX Mistakes to Improve Core Web Vitals?

Improving Core Web Vitals requires a combination of performance optimization and smart design choices. Below are detailed, actionable strategies to fix the UI/UX performance issues discussed earlier and build a website that loads faster, feels stable, and responds instantly to user interactions.

1. Optimize Images and Media

Images are often the largest elements on a page, making them one of the biggest contributors to slow LCP scores. Proper optimization ensures fast loading without compromising design quality.

How to fix it:

• Use modern image formats (WebP/AVIF): These formats drastically reduce file size while maintaining high visual quality, improving LCP for image-heavy pages.
• Compress images before upload: Tools like Image Optimizer Pro help remove unnecessary data and reduce overhead.
• Always define image dimensions: Adding width and height attributes prevents layout shifts and stabilizes CLS.
• Use responsive images (srcset and sizes): This ensures users receive image sizes appropriate for their device, reducing unnecessary bandwidth.
• Lazy load below-the-fold media: Delaying non-critical media improves initial load and keeps the page visually stable.

2. Reduce Layout Shifts (Improve CLS)

Layout shifts happen when content moves unexpectedly during loading. Preventing this keeps your layout predictable and meets user expectations.

How to fix it:

• Reserve space for ads, pop-ups, and dynamic elements: Allocate fixed dimensions in the layout so late loading doesn’t push content.
• Preload fonts: Prevents sudden text jumps when fonts load, reducing CLS.
• Use proper CSS rules to stabilize elements: For example, assigning a fixed height to images or banners avoids unexpected reflows.
• Use skeleton loaders or placeholders: These give users a stable structure while content loads, improving perceived performance and reducing distractions.
• Avoid inserting content above existing content: This ensures the layout remains stable as additional elements load.

3. Streamline Navigation

Heavy menus, mega-menus, and script-based navigations often slow down interactivity and add visual clutter. A lighter, simplified navigation enhances both UX and performance.

How to fix it:

• Use lightweight, minimal navigation layouts: Avoid multi-layered menus unless absolutely necessary.
• Reduce animation-heavy scripts: Heavy animations can block rendering and slow down tap or click response.
• Prioritize mobile-first interaction design: Ensure the menu opens quickly, touch targets are large enough, and the navigation doesn’t require heavy JavaScript.
• Use CSS-based menus where possible: CSS interactions typically load faster and require fewer resources than JS-driven menus.

4. Improve Responsiveness and INP (Interaction to Next Paint)

INP measures how fast your site responds to user interactions. Heavy JavaScript is the biggest culprit behind slow INP, blocking the main thread and delaying responses.

How to fix it:

• Reduce JavaScript bundle size: Eliminate scripts you don’t use and split large bundles so the browser loads only what’s needed initially.
• Break long tasks into smaller chunks: Long JavaScript tasks freeze the main thread. Breaking them improves interaction responsiveness.
• Use browser-native interactions: For example, using
  tags instead of JS-driven accordions.
• Remove unnecessary third-party scripts: Heavy tracking scripts, widgets, pop-ups, and libraries often degrade INP.
• Defer non-essential JavaScript: Allow critical content to load first while secondary scripts load later.

5. Fix Typography Delays (Fonts and Rendering)

Fonts directly impact CLS and loading behavior. Poor font management can cause huge visual shifts and invisible text during load.

How to fix it:

• Limit the number of font families and weights: Using too many increases file sizes and slows initial loading.
• Use font-display: swap: Ensures text appears immediately using a fallback font, preventing FOIT (flash of invisible text).
• Preload above-the-fold fonts: Prioritizes essential text for quicker rendering.
• Subset fonts to reduce file size: Remove unused glyphs to reduce font file weight and improve speed.
• Use variable fonts: Single-file variable fonts often load faster than multiple-weight files.

6. Optimize Mobile Layouts

Mobile-first performance is essential since a significant percentage of global traffic comes from mobile devices. Poor mobile design affects LCP, CLS, and INP more than desktop layouts.

How to fix it:

• Adjust spacing and layout for small screens: Proper spacing prevents overlap and ensures smooth layout rendering.
• Ensure images and grids scale properly: Use responsive CSS units like %, rem, and flexible containers to reduce layout thrashing.
• Improve touch targets: Make sure buttons are large enough to prevent mis-taps, which also enhances usability.
• Use CSS containment: This helps control layout calculations and prevents unnecessary reflows.
• Avoid complex layouts: Multi-column or overly dense layouts slow rendering and cause shifts on mobile devices.

7. Reduce Visual Noise and UI Clutter

Visual clutter increases cognitive load and slows down perceived performance. Simplifying the interface can streamline user intent and improve performance scores.

How to fix it:

• Remove unnecessary UI elements: Eliminate decorative icons, extra banners, and redundant content to reduce DOM size and speed up initial rendering.
• Use whitespace intentionally: Balanced spacing helps users scan content quickly, reduces visual chaos, and improves how smoothly elements load into view.
• Minimize foreground images: Large hero graphics, decorative images, and overlapping visual components require more rendering time and contribute to slower LCP.
• Remove repetitive or irrelevant components: Carousels, duplicated CTAs, or unnecessary badges increase layout complexity and may cause unstable rendering or jumps.

8. Replace Heavy Libraries With Modern, Lightweight Alternatives

Bloated scripts are a major cause of slow loading (LCP) and delayed interactions (INP).

Optimizations include:

• Replace jQuery with vanilla JavaScript: Most modern browsers support all functions natively, eliminating the need for a 90KB library that delays script execution.
• Use SVG icons instead of icon fonts or PNG sets: SVGs are scalable, smaller, and render faster than multiple PNG images or entire font libraries.
• Use CSS animations over JS animation libraries: CSS animations are hardware-accelerated and require fewer CPU resources, improving responsiveness and reducing jank during interactions.
• Adopt lightweight frameworks: If you need JavaScript frameworks, consider Preact, Svelte, or SolidJS instead of heavy options. These reduce bundle size dramatically.

9. Optimize Third-Party Code

Third-party scripts (analytics, ads, widgets, A/B testing tools) often harm performance.

• Load third-party tools asynchronously: Deferred or Asynchronous loading prevents external scripts from blocking critical rendering paths, improving both LCP and INP.
• Remove unused or legacy scripts: Remove old tracking pixels, outdated analytics tools, or inactive tag managers that add unnecessary overhead and delay interaction times.
• Self-host critical assets where possible: When allowed, self-host fonts, scripts, and essential libraries to reduce DNS lookups and improve loading reliability.
• Use server-side tracking when possible: Replace JavaScript-heavy client-side analytics with server-side solutions to reduce script execution time and minimize main-thread blocking.

By implementing these performance-forward UI/UX improvements, you not only fix major Core Web Vitals issues but also create a smoother, more intuitive browsing experience for users. Strong performance is a competitive advantage, and combining optimized design with efficient code ensures your website remains fast, stable, and responsive across all devices.

Best Practices for a Core-Web-Vitals-Friendly User Experience

To maintain strong Core Web Vitals performance over the long term, designers and developers should combine usability principles with performance-focused decision-making. These best practices help reduce recurring UI/UX performance issues and ensure a consistently smooth user experience.

• Follow a Mobile-First Approach

Design for small screens first, where layout constraints are tight, and performance issues are more noticeable. This ensures cleaner structure, fewer layout shifts, and faster loading across all devices.

• Use a Clean, Minimal Design to Reduce Visual Load

Minimalism lowers cognitive load and reduces the number of DOM elements the browser must render. Fewer distractions also support better engagement and improved load performance.

• Prioritize Above-the-Fold Content in Loading Order

Loading visible content first helps improve LCP and creates a faster-perceived experience. Defer scripts, images, and sections that appear further down the page.

• Reduce Unnecessary Animations or Transitions

Heavy animations can trigger layout recalculations and long main-thread tasks, hurting INP. Use subtle, lightweight transitions only when they enhance clarity or user actions.

• Combine Usability Testing with Performance Testing

Evaluate not only how users interact with your site but also how fast elements respond during those interactions. Pairing UX insights with Core Web Vitals data gives a complete optimization picture.

• Keep Scripts Lightweight and Modular

Break code into smaller chunks and load only what’s required on each page. Modular JS reduces main-thread blocking and ensures interactions remain smooth.

• Replace Heavy Libraries with Native Browser Features

Modern browsers support many features natively—like dialog boxes, lazy loading, and smooth scrolling, without additional libraries. This reduces script weight and speeds up interactions.

• Conduct Regular Performance Audits

Use tools like Lighthouse, PageSpeed Insights, and DevTools to frequently check for regressions. Routine audits help catch new UI components, scripts, or design elements that degrade Core Web Vitals over time.

Conclusion

Poor design choices can significantly decrease the stability, interactivity, and loading speed of a website. Many sites struggle with design and user-related issues, all of which are avoidable.

By identifying these UI/UX mistakes and fixing them with a performance-centered mindset, you can drastically improve Core Web Vitals, which leads to better rankings, higher engagement, and a more seamless user experience.

A thoughtful approach to UI/UX design not only enhances aesthetics but ensures your website remains fast, stable, and responsive for all users.

FAQs

1. How do UI/UX mistakes affect Core Web Vitals?

Poor design decisions, such as heavy visuals, unstable layouts, or interaction delays, directly increase LCP, CLS, and INP, making your site slower, less responsive, and less user-friendly.

2. Which UI/UX mistakes most commonly hurt performance?

Common issues include unoptimized images, excessive JavaScript, cluttered layouts, intrusive pop-ups, inconsistent spacing, and poorly structured mobile designs. These add rendering load and disrupt user flow.

3. How can improving UI/UX help my SEO?

Google uses Core Web Vitals as ranking signals. A cleaner, faster, and more responsive UI improves user engagement and helps boost search rankings by meeting Google's performance standards.

4. What is the quickest way to improve Core Web Vitals?

Start by optimizing images, reducing third-party scripts, fixing layout shifts, simplifying the design, and minimizing JavaScript. These changes deliver immediate LCP, CLS, and INP improvements.

5. Which tools help detect UI/UX issues affecting Core Web Vitals?

Tools like Google PageSpeed Insights, Lighthouse, WebPageTest, GTmetrix, Hotjar, and Chrome DevTools reveal slow elements, layout instability, heavy scripts, and UX friction points impacting performance.