Free tool
Core Web Vitals budget calculator
Enter the LCP, INP and CLS you measured and see where each one sits against the published thresholds. Then set a load time target and get a page weight budget to build toward.
Short answer: The Core Web Vitals good thresholds are Largest Contentful Paint at 2.5 seconds or less, Interaction to Next Paint at 200 milliseconds or less and Cumulative Layout Shift at 0.1 or less, measured at the 75th percentile of page loads. This browser calculator checks your own figures against those thresholds and estimates how many KB of critical files fit a load time target for a connection speed and server response time you choose.
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Results
Enter a figure to see results. This needs scripting on.
The thresholds this tool uses
From the web.dev articles on LCP, INP and CLS (read Nov 10, 2026). Each is judged at the 75th percentile of page loads, separately for mobile and desktop.
| Metric | Good | Needs improvement | Poor |
|---|---|---|---|
| LCP | 2.5 s or less | 2.5 s to 4.0 s | Over 4.0 s |
| INP | 200 ms or less | 200 ms to 500 ms | Over 500 ms |
| CLS | 0.1 or less | 0.1 to 0.25 | Over 0.25 |
What we make of this
The weight budget is the part of this page we added, and it comes with limits. It treats every critical byte as arriving one after another over one connection, which overstates the time on a fast, well-cached page and understates it on a page with many third-party hosts. Use it to compare designs against each other and to say no to a hero video, not to predict a score.
A poor LCP with a small page weight usually points at the server response time or a late-discovered LCP image. A good LCP with a poor INP points at JavaScript running after the page appears. Those are different fixes, which is why the metrics are shown separately. Hamza Rivera wrote and maintains this tool; the method is above and every threshold is dated.
Want someone to find the cause on a real site? See our technical SEO services, or browse all free SEO tools. If you are moving to a new site, the SEO migration checklist covers speed checks before launch.
Questions about Core Web Vitals budgets
What are the Core Web Vitals thresholds?
web.dev (read Nov 10, 2026) lists these as good: Largest Contentful Paint (LCP) at 2.5 seconds or less, Interaction to Next Paint (INP) at 200 milliseconds or less, and Cumulative Layout Shift (CLS) at 0.1 or less. Poor values are LCP above 4.0 seconds, INP above 500 milliseconds and CLS above 0.25. Anything between good and poor is "needs improvement".
Which numbers should I type in for LCP, INP and CLS?
Use field data if you can get it, such as the Core Web Vitals report in Search Console or the Chrome UX Report. web.dev (read Nov 10, 2026) says a page passes when the 75th percentile of page loads meets the good threshold, assessed separately for mobile and desktop. A single lab run from your own laptop is a useful test, but it is one visit, not the 75th percentile of real ones.
How does the page weight budget work?
It is a planning estimate we built, not a measurement. You give a load time target, your server response time and a connection speed. The calculator subtracts the server response, two round trips for connection setup and a render allowance, and turns the remaining time into the number of KB a connection of that speed can deliver. Real pages differ because of caching, compression, parallel downloads and what the browser decides to load first, so treat the result as a ceiling to design toward and confirm with a real test.
Which files count toward the budget?
The calculator counts the HTML, CSS, JavaScript, fonts and the LCP image, because those are on the path to the largest element appearing. web.dev (read Nov 10, 2026) lists images, SVG images, video posters, CSS background images and block-level text as what can become the LCP element. Images below the fold and scripts that load after the page is visible matter for INP and total weight, so use the extra field for them.
Is anything I type sent anywhere?
No. The arithmetic runs in your browser with JavaScript. The exported file is built on your device.
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