Core Web Vitals in 2026: Why INP Is Costing You Conversions
Interaction to Next Paint measures how quickly your site responds when someone taps. Slow interactions quietly kill mobile sales — here's how to find and fix them.
Most teams know their site should load fast. Fewer realise that a page can load quickly and still feel broken — a button that takes a beat to respond, a filter that freezes, a menu that lags behind the tap. That sluggishness is what Interaction to Next Paint (INP) measures, and it has been one of Google's Core Web Vitals since it replaced First Input Delay in 2024.
The three numbers to watch
- Largest Contentful Paint (LCP): how quickly the main content appears — aim for 2.5 seconds or less
- Interaction to Next Paint (INP): how quickly the page responds to taps, clicks and typing — aim for 200 milliseconds or less
- Cumulative Layout Shift (CLS): how much the layout jumps around while loading — aim for 0.1 or less
These thresholds are measured on real users, typically at the 75th percentile. That means your slowest meaningful group of visitors — often on mid-range Android phones and patchy mobile networks — sets your score, not the fast laptop in the office.
What usually causes poor INP
- Too much JavaScript running on the main thread, especially during page load
- Heavy third-party scripts: chat widgets, tag managers, heatmaps, A/B testing tools
- Large client-side re-renders when a user filters, sorts or opens a menu
- Event handlers that do expensive work before giving visual feedback
Fixes that tend to pay back fastest
Start with field data from Google Search Console and PageSpeed Insights to find the templates that fail, then reproduce the slow interactions in Chrome DevTools. The biggest wins usually come from removing or delaying third-party scripts, shipping less JavaScript by rendering more on the server, breaking long tasks into smaller chunks, and showing immediate visual feedback before heavier work finishes.
Performance isn't a vanity score. Every extra moment of lag is a chance for a mobile buyer to give up. Treat INP as a conversion metric, and review it every time a new script or feature goes live.