What Is INP (Interaction to Next Paint) and Why Did It Replace FID?

Interaction to Next Paint (INP) is the newest of Google’s Core Web Vitals, officially replacing First Input Delay (FID) in March 2024. While FID only measured the delay before the browser began processing your very first tap or click, INP measures the full responsiveness of every interaction throughout a page visit — clicks, taps, and keyboard input — and reports the worst-performing one.

Google considers an INP of 200 milliseconds or under to be “good”, between 200 and 500 ms “needs improvement”, and above 500 ms “poor”. A poor INP means your page feels sluggish when visitors try to interact with it — buttons that don’t respond instantly, forms that lag, and menus that are slow to open — all of which increase frustration and the likelihood of a visitor leaving.

Why INP Is a Better Measure Than FID

FID had a significant blind spot: it only measured the input delay for the first interaction on a page. If a visitor clicked a link within a second of the page loading, FID captured that. But if the page became unresponsive after a few seconds of JavaScript executing in the background — a common scenario with heavy single-page applications — FID would never detect that problem.

INP covers every interaction during the visit and picks the worst one. This makes it a far more representative measure of how responsive your site actually feels. A page could score well on FID simply by being static for the first second, while being genuinely unusable during normal browsing. INP closes that gap.

Common Causes of a Poor INP Score

Long JavaScript tasks are the primary culprit. When the browser’s main thread is busy executing a large chunk of JavaScript — parsing a framework, running an analytics script, or processing data — any interaction the user makes has to wait until that task finishes before the browser can respond. Tasks that run for longer than 50 ms on the main thread are considered “long tasks” and are the first thing to investigate.

Third-party scripts are a major contributor. Tag managers, chat widgets, ad scripts, and A/B testing platforms all compete for the main thread. Poorly optimised React or Vue component re-renders that update the DOM unnecessarily can also spike INP. On mobile devices, where CPU power is more limited, these problems are amplified significantly.

How to Improve Your INP Score

The most effective strategies are breaking up long JavaScript tasks using “yield to the main thread” patterns (such as “scheduler.postTask” or “setTimeout” breaks), deferring non-critical third-party scripts, and auditing your tag manager to remove unused tags. For frameworks, investigate unnecessary re-renders and consider code-splitting to reduce the amount of JavaScript that runs upfront.

Use Chrome DevTools’ Performance panel and the Interaction to Next Paint overlay to identify which interactions are slow and which long tasks are blocking them. Google Search Console’s Core Web Vitals report will show your real-world INP from actual Chrome users, broken down by mobile and desktop. Prioritise mobile, as that’s where poor INP scores are most common and most damaging to both user experience and rankings.