INP (Interaction to Next Paint)

INP (Interaction to Next Paint) is a Core Web Vitals metric that measures page responsiveness — the delay between a user interaction and the moment the browser displays a visible response. In March 2024 INP replaced the earlier FID metric as Google's official responsiveness signal in ranking. Unlike its predecessor, INP observes every interaction throughout the whole visit, not just the first one.

How INP works

Whenever a user clicks, taps or presses a key, the browser measures the time from that event to the next paint that reflects the result of the action. Three phases add up to the score:

• input delay — the wait before the browser can start handling the event, often blocked by a busy main thread;
• processing time — execution of the JavaScript tied to the event;
• presentation delay — recalculating layout and rendering the new frame.

As its final value INP reports the worst (or near-worst) interaction across the visit, which reflects how the page actually feels to use.

Practical applications

INP is measured on field data, including the Chrome User Experience Report and Search Console reports. The most common cause of poor scores is heavy JavaScript blocking the main thread. Improvements come from splitting long tasks into smaller ones, trimming third-party scripts, deferring non-critical code, using web workers and debouncing frequent events. A responsive interface lowers bounce rates and lifts conversions, which is why INP is a key part of optimising page experience. It is worth remembering that lab tools such as Lighthouse cannot measure INP directly, because it requires genuine user interactions — only field data collected from real visitors' browsers gives the full picture. In practice, INP optimisation is iterative: you identify the slowest interactions on key pages, profile the main thread in developer tools and then cut the event processing time. Improving INP goes hand in hand with overall page performance hygiene and pays off most on weaker mobile devices, where heavy JavaScript blocks the thread the hardest.