INP Is the New Page Speed: What UK Site Owners Must Fix Before 2027

What INP measures and why Google cares

Interaction to Next Paint times how long, in milliseconds, your site takes to visually respond after a user taps, clicks or keys. Below 200ms is "good", over 500ms is "poor". Google now uses INP as one of its three Core Web Vital signals, and pages with poor INP are quietly ranking lower since the May 2025 update.

Why most UK sites are failing

Three culprits dominate: heavy third-party tags (chat widgets, ad pixels, A/B-test scripts), large React/Vue bundles that block the main thread on tap, and bloated CMS themes (looking at you, WooCommerce + 14 plugins). The same site can feel fast on broadband Chrome and miserable on a 4G phone in Birmingham.

How to diagnose your INP

Open Chrome DevTools, switch to the Performance tab, throttle to "Slow 4G" and "4× CPU slowdown", record an interaction. Anything over 200ms shows up red. PageSpeed Insights, CrUX dashboard and Search Console all give field-data INP scores too — start there.

Five fixes that move the needle

• Defer or remove non-critical scripts — chat widgets, analytics, A/B tests can almost always load lazily after first interaction.
• Break up long tasks — anything over 50ms blocks the main thread. Use scheduler.yield() or requestIdleCallback to chunk work.
• Server-render expensive routes — Next.js and Astro will both shave 200–400ms off first interaction by sending HTML, not JSON.
• Audit your tag manager — every tag is a tax. Most UK sites can safely cut 30–50% of GTM tags without losing meaningful data.
• Image and font discipline — convert to AVIF/WebP, preload critical fonts, kill webfonts you do not actually use.

A 2-week roadmap

Week 1: measure baseline, identify worst offenders, kill obvious bloat. Week 2: defer remaining scripts, optimise images, retest. Most sites can move from poor (>500ms) to good (<200ms) inside two weeks of focused effort. The SEO impact starts showing up within 30 days.