Interaction to Next Paint

Written by Cobus van der Westhuizen, reviewed by Wynand van der Westhuizen, fact-checked by Lenata Oosthuizen. Last reviewed July 2026. Editorial policy.

What Is Interaction to Next Paint?

Interaction to Next Paint (INP) is one of Google's three Core Web Vitals. It measures the time between a user interacting with a page (by clicking a button, tapping a link, or pressing a key) and the browser visually responding to that interaction. INP captures all qualifying interactions across an entire page visit, then reports the worst-case latency observed. This makes it a demanding but realistic measure of how responsive a site feels during normal use.

INP replaced First Input Delay (FID) as an official Core Web Vital in March 2024. FID only measured the delay before the browser could begin processing the first interaction on a page, which was a limited snapshot. INP's whole-session approach is a much stricter test of JavaScript performance and main thread availability.

Google's INP thresholds are: under 200 milliseconds is good, 200 to 500 milliseconds needs improvement, and above 500 milliseconds is poor. These are measured at the 75th percentile of user sessions collected through Chrome's user experience data (CrUX). For South African websites, where users may be on lower-specification mobile devices with less processing power, achieving a consistently good INP score requires careful JavaScript management.

The root cause of most poor INP scores is long tasks on the browser's main thread. When JavaScript is executing, the browser cannot respond to user input. A long task is any task that takes more than 50 milliseconds. Heavy frameworks, large third-party analytics scripts, and event handler functions that do too much synchronous work are the most common culprits. Improving INP is primarily a front-end engineering concern, though it has direct implications for SEO and conversions.

Interaction to Next Paint In Practice

A South African e-commerce site running WooCommerce often accumulates numerous third-party scripts: a live chat widget, a marketing automation pixel, a retargeting tag, and perhaps a loyalty programme script. Each of these competes for the browser's main thread. When a shopper clicks "Add to Cart," the browser may need to finish executing a chunk of third-party JavaScript before it can process the click event and update the cart UI. The visible delay between the click and the cart updating is what INP measures.

Practical fixes include auditing and removing unused scripts, loading third-party scripts asynchronously or with defer attributes, breaking large JavaScript tasks into smaller chunks using scheduler.postTask or setTimeout(0) patterns, and reducing the complexity of event handlers. Google's PageSpeed Insights and Chrome DevTools both provide INP diagnostics including a breakdown of which interactions are slow and what long tasks are occurring at the time.

For WordPress sites specifically, disabling unnecessary plugins (particularly those that inject scripts on every page), switching to a lightweight theme, and enabling a caching layer often produces measurable INP improvements without requiring deep JavaScript knowledge. The key is reducing the total amount of JavaScript the browser needs to parse and execute on each page load.

How Interaction to Next Paint is measured

Interaction to Next Paint (INP) is a Core Web Vital that measures a page's responsiveness, how quickly it visually responds to a user's interactions such as taps, clicks and key presses. It replaced First Input Delay (FID) as a Core Web Vital in 2024, and it is a more complete measure: where FID assessed only the delay of the first interaction, INP considers interactions throughout the visit and reports a value representative of the page's overall responsiveness, capturing the worst-felt delays. For each interaction, it measures the time from the user acting to the next visual update on screen, and a good INP is 200 milliseconds or less, with higher values indicating sluggishness that users feel as lag. Google measures INP from real users, so it reflects genuine experience across devices and conditions. Because it captures responsiveness across a whole visit rather than one moment, INP better represents whether a page feels quick and responsive to use.

How to improve INP

Improving INP targets what makes a page slow to respond to interactions, which is largely heavy work on the browser's main thread, typically JavaScript, that blocks the page from reacting promptly. The main approaches are to reduce and optimise JavaScript so less runs and blocks; break up long tasks into smaller pieces so the browser can respond to input between them rather than being tied up; defer non-essential scripts so they do not compete with interactions; and minimise the work done in response to an interaction so the visual update comes quickly. Because INP reflects responsiveness across the whole visit, the aim is a page that reacts promptly to every interaction, not just the first. Measuring with real-user field data in Search Console identifies where responsiveness is poor, since Google uses field data. Improving INP both lifts the Core Web Vital and removes the genuine frustration of a page that lags when tapped or clicked, which directly affects how usable and pleasant a page feels.

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