Introduction
Google’s Core Web Vitals have become central to how websites are ranked and experienced. In 2025, Google officially replaced First Input Delay (FID) with a new metric — Interaction to Next Paint (INP).
If you manage a WordPress site, this change matters. INP measures how quickly a page responds to any user interaction (click, tap, keyboard input) — not just the first one. High INP values can lower your rankings and frustrate visitors.
Let’s look at what’s new for 2025 and how to optimise your WordPress site to achieve a great INP score.
Understanding INP
INP (Interaction to Next Paint) measures the total time from a user’s interaction to when the browser visually updates.
Google’s thresholds:
- Good: ≤ 200 ms
- Needs improvement: 200–500 ms
- Poor: > 500 ms
Unlike FID, which only looked at the first interaction, INP tracks the worst-case interactions across an entire session.
Why INP Replaced FID
FID was a limited metric. A page could look fine initially but lag badly on later interactions — such as opening menus, switching tabs, or filtering results. INP offers a more complete reflection of real-world responsiveness.
For WordPress sites that use heavy page builders, large JavaScript bundles, or unoptimised plugins, INP often becomes a bottleneck.
How to Improve INP on WordPress
1. Minimise Main-Thread Blocking
The main thread handles rendering, JavaScript, and user interactions. If it’s overloaded, INP suffers.
- Combine and defer scripts: Use plugins like Asset CleanUp or Perfmatters to manage JS loading.
- Defer non-critical scripts:
<script src="script.js" defer></script> - Avoid render-blocking CSS: Use
media="print"orasyncloading for large stylesheets.
2. Optimise Fonts
Font loading has a measurable impact on INP.
- Add
font-display: swap;in your theme’s stylesheet. - Host fonts locally (especially Google Fonts).
- Preload key fonts in
theme.json:
"settings": {
"typography": {
"fontFamilies": [
{
"fontFamily": "Inter, sans-serif",
"slug": "inter",
"fontFace": [
{
"fontFamily": "Inter",
"src": "url('/wp-content/fonts/inter.woff2') format('woff2')",
"fontDisplay": "swap"
}
]
}
]
}
}3. Use theme.json for Performance
WordPress’s theme.json isn’t just about styling — it controls how assets are loaded.
- Global settings: Simplify block styles to reduce unused CSS.
- Disable unneeded features:
"settings": {
"custom": {
"spacing": false,
"typography": false
}
}- Consolidate design tokens so the editor and front end use the same CSS variables (fewer style recalculations).
4. Adopt the Interactivity API
Introduced in 2024 and expanded in 2025, the WordPress Interactivity API replaces many legacy front-end JavaScript hacks.
Benefits:
- Smaller JS payloads.
- Better browser scheduling for tasks.
- Seamless state management without bloated frameworks.
Plugins and themes built on the new API deliver far better INP results by reducing blocking scripts.
5. Lazy-Load and Optimise Media
Large images and video embeds cause layout shifts and interaction delays.
- Enable native lazy loading:
<img src="image.jpg" loading="lazy" alt="...">- Compress and resize media: Tools like Imagify or ShortPixel integrate directly with WordPress.
- Avoid autoplay or oversized hero videos.
Measuring Your INP
Tools to track real metrics:
- PageSpeed Insights — see INP, LCP, CLS per page.
- Chrome User Experience Report (CrUX) — actual field data from users.
- Lighthouse / WebPageTest — synthetic testing for lab environments.
Tip: Test logged-in vs logged-out views; plugin dashboards and editors can skew data.
Making WordPress Faster for 2025 and Beyond
Core Web Vitals are no longer optional. INP brings user experience and SEO closer than ever — and WordPress provides the tools you need to succeed: theme.json, lazy loading, caching, and the new Interactivity API.
If you’d like ThriveWP to audit your site’s Core Web Vitals and implement proven performance fixes, our team can ensure your WordPress site is fast, stable, and future-ready.
