Performance · November 3, 2026 · 5 min read
Core Web Vitals in 2026: Why INP Decides How Fast Your Site Feels
A website can look fast and still feel slow. Core Web Vitals measure the difference — and in 2026, Interaction to Next Paint is the metric most sites struggle with.
The three metrics, and the thresholds that matter
Google’s Core Web Vitals measure real-user experience across three dimensions. Largest Contentful Paint (LCP) tracks loading and should be 2.5 seconds or less. Interaction to Next Paint (INP) tracks responsiveness and should be 200 milliseconds or less. Cumulative Layout Shift (CLS) tracks visual stability and should stay at 0.1 or below. Each is assessed at the 75th percentile of real visits.
Why INP is the hard one
INP replaced First Input Delay as a Core Web Vital in March 2024. Where FID only measured the delay before the first interaction was handled, INP looks at interactions throughout the whole visit — clicks, taps and key presses — from input until the next frame is painted. Heavy JavaScript, large component trees and third-party scripts are the usual culprits.
Practical fixes for INP
Break up long tasks so the main thread can respond between them, and move heavy work off the main thread with web workers. Audit third-party scripts: chat widgets, trackers and tag managers often add the most delay. Give immediate visual feedback on interaction, then do the expensive work afterwards.
Don’t forget LCP and CLS
For LCP, keep the hero image small, use modern formats such as AVIF or WebP, prioritise it, and avoid hiding it behind client-side rendering. For CLS, reserve space for images, embeds and web fonts so content never jumps while the page loads.
Field data beats lab data
Lighthouse is great for debugging, but Google evaluates real-user data from the Chrome UX Report. Check the Core Web Vitals report in Search Console and the field data in PageSpeed Insights to see what your visitors actually experience.
Key takeaways
Targets at the 75th percentile: LCP ≤ 2.5 s, INP ≤ 200 ms, CLS ≤ 0.1.
Audit third-party scripts — they are often the biggest INP cost.
Optimise for field data, not just a Lighthouse score.
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