Core Web Vitals in 2026: What's Changed

The Evolution of Core Web Vitals

Core Web Vitals have been a ranking factor since 2021, but Google continues to refine the metrics. The biggest change in 2024 was replacing First Input Delay (FID) with Interaction to Next Paint (INP), and this has significant implications for how we optimize websites.

The Three Core Metrics

Largest Contentful Paint (LCP)

LCP measures loading performance—specifically, how long it takes for the largest content element to become visible. The target remains under 2.5 seconds.

What's new: Google now provides better debugging tools and more granular sub-part timing (TTFB, resource load time, element render delay).

Interaction to Next Paint (INP)

INP replaced FID as the responsiveness metric. While FID only measured the first interaction, INP measures the latency of all interactions throughout the page lifecycle, reporting the worst (or near-worst) interaction.

Target: Under 200 milliseconds for a "good" score.

Why it matters: Many sites that passed FID fail INP because they have slow subsequent interactions, not just slow first interactions.

Cumulative Layout Shift (CLS)

CLS measures visual stability—how much the page layout shifts unexpectedly during loading. The target is under 0.1.

Recent clarification: Google now uses a "session windows" approach, measuring the maximum session window of layout shifts rather than cumulative total. This better reflects actual user experience.

Optimizing for INP

Since INP is the newest metric, many teams struggle with optimization. Here are key strategies:

1. Break Up Long Tasks

JavaScript tasks over 50ms block the main thread. Use setTimeout, requestIdleCallback, or the Scheduler API to break up work.

2. Prioritize Input Handlers

Event handlers should do minimal work. Defer non-essential updates using requestAnimationFrame or microtasks.

3. Use Web Workers

Move heavy computation off the main thread. Web Workers can handle data processing, complex calculations, and other intensive tasks.

4. Optimize Rendering

Minimize DOM size and complexity. Use CSS containment (contain: content) to isolate rendering. Virtualize long lists.

Measuring in the Field

Lab tools like Lighthouse are useful for debugging, but Core Web Vitals rankings are based on real-user data from the Chrome User Experience Report (CrUX). Ensure you're monitoring field data through:

• Google Search Console Core Web Vitals report
• PageSpeed Insights (shows both lab and field data)
• web-vitals JavaScript library for custom RUM