March 2024: Google replaced FID with INP (Interaction to Next Paint). In 2026 INP is a hard ranking signal — and most WordPress sites miss the 200 ms bar. This guide covers measurement, fixes, and why Next.js 16 clears INP by architecture.
What INP is and why it replaced FID
INP measures the worst interaction latency across the whole page life — not just the first tap. It includes input delay, processing time and presentation delay.
Google thresholds
Google uses p75 from 28 days of CrUX field data — not a lab Lighthouse run.
Why WordPress fails INP
- Heavy jQuery plugins (Elementor, popups) running on click.
- Long tasks > 50 ms from chat widgets, GTM and trackers.
- No debounce/throttle on scroll and input.
How Next.js 16 fixes INP structurally
- React Server Components — handlers stay on the server, tiny client JS.
- Automatic code splitting — only the route’s JS hits the main thread.
- Streaming + PPR — the shell is interactive while the rest hydrates.
FAQ
INP vs FID?
FID measured only the first input delay. INP takes the worst interaction in the session, including processing and paint.
Can I measure INP locally?
Yes — DevTools Performance. For SEO, only CrUX p75 counts.
Want INP < 50 ms and TOP 3 rankings?
Free Core Web Vitals audit with INP, LCP, CLS and a 2-hour fix plan.
Request a CWV auditReady to implement this in your project?
