What is Interaction to Next Paint (INP)?

Interaction to Next Paint (INP) measures how quickly a website visibly responds after a user interaction. It includes interactions such as clicks, taps and keyboard input, moments where visitors expect immediate feedback.

Why did INP replace First Input Delay?

INP is one of the Core Web Vitals and replaced First Input Delay (FID) as the responsiveness metric on March 12, 2024. The reason is simple: FID only looked at the first input delay. INP evaluates interactions across the whole page visit and is therefore closer to the actual user experience.

A good INP is 200 milliseconds or less. Between 200 and 500 milliseconds, improvement is recommended. Values above 500 milliseconds are considered poor. At that level, a website feels noticeably sluggish even if it is already visually loaded.

What causes poor INP values?

INP problems often result from heavy JavaScript work on the main thread. When the browser is executing large scripts, it cannot respond immediately to user input. Typical causes include tracking and marketing scripts, complex sliders, page builder logic, chat widgets, unused JavaScript bundles or expensive event handlers.

In WordPress websites, these effects often come from plugin combinations. One plugin may look harmless, but several small script sources together can make buttons, menus or form fields react with delay.

INP can also stand out on pages that feel fast at first glance. The page is visible, but the browser is still busy in the background. That is exactly where the noticeable gap between user action and visible response appears.

Why does INP matter for businesses?

INP is not only a technical value. If a contact form responds late, a menu opens slowly or a shop button gives delayed feedback, the page feels unreliable. Users click twice, abandon the process or lose trust.

That is why INP should be evaluated together with Largest Contentful Paint (LCP) and Cumulative Layout Shift (CLS). LCP describes the first visible impression; INP describes how usable the page remains afterwards.

How can INP be improved?

Good performance optimization reduces unnecessary JavaScript work and prioritizes real user interactions. This includes removing unused scripts, splitting long tasks, delaying non-critical services and checking plugins that output assets on every page.

Architecture also matters. Static content should not require unnecessary client-side JavaScript. Interactive functions should be loaded only where they are needed. For detailed analysis, Chrome DevTools, Lighthouse, PageSpeed Insights and the web.dev documentation on Interaction to Next Paint are useful.

In implementation, it is worth focusing on the most important user journeys: opening navigation, filling out a form, using filters, adding a product to the cart or switching contact tabs. These are the moments where a page has to react immediately because delays directly affect trust and conversion probability.