The State of Web Vitals

Main-thread CPU breakdown on React sites

30.5% of audited sites (2,918) spend over 1,200ms in main-thread scripting during load, pushing median field INP to 105ms (89% good INP) versus 79ms (94% good INP) at 150 to 450ms.

Field data PhoneDesktopAll Scope All sites October 2026 edition · Phone field outcomes · React sites only
React Scoped to 9,570 sites out of 210,902 analyzed (frameworks) Compare with all sites →

4.5% of React sites use under 150ms of scripting CPU main-thread CPU breakdown, and 95% of those sites have a good INP, against 92% of all React sites.

The State of Web Vitals · October 2026 · React: 9,570 crawled sites · 5,488 with phone field dataBy Arjen Karel · corewebvitals.io/state-of-cwv
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INP pass rate

Sites with under 150ms of scripting CPU main-thread CPU breakdown have a good INP most often: 95%, against 92% of all React sites. Sites with over 1,200ms of scripting CPU scripting CPU have it least often, at 89%.

SitesGood, needs improvement, poor INPMedian
All React sites5,48892%90ms
Under 150ms scripting CPU 4.5%22695%94ms
150 to 450ms scripting CPU 26.3%1,44894%79ms
450 to 1,200ms scripting CPU 38.6%2,09994%87ms
Over 1,200ms scripting CPU 30.5%1,71589%105ms
GoodNeeds improvementPoorSites: with Chrome field data
The State of Web Vitals · October 2026 · React: 9,570 crawled sites · 5,488 with phone field dataBy Arjen Karel · corewebvitals.io/state-of-cwv
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Main-thread CPU breakdown usage

450 to 1,200ms of scripting CPU is the most used: 38.6% of React sites. Under 150ms of scripting CPU is 4.5% of React sites.

450 to 1,200ms scripting CPU 38.6% Over 1,200ms scripting CPU 30.5% 150 to 450ms scripting CPU 26.3%
450 to 1,200ms scripting CPU 38.6% Over 1,200ms scripting CPU 30.5% 150 to 450ms scripting CPU 26.3% Under 150ms scripting CPU 4.5%
The State of Web Vitals · October 2026 · React: 9,570 crawled sites · 5,488 with phone field dataBy Arjen Karel · corewebvitals.io/state-of-cwv
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Main-thread CPU breakdown per platform

On Wix, 44% of sites use 450 to 1,200ms of scripting CPU main-thread CPU breakdown, and 96% of Wix sites have a good INP, against 92% of all sites. On WordPress, 47% of sites use over 1,200ms of scripting CPU, and 96% of WordPress sites have a good INP.

PlatformMain-thread CPU breakdown on its sitesGood INP
All React sites 9,570 sites450 to 1,200ms scripting CPU 39%Over 1,200ms scripting CPU 30%150 to 450ms scripting CPU 26%92%
Wix 5,824 sites450 to 1,200ms scripting CPU 44%150 to 450ms scripting CPU 31%Over 1,200ms scripting CPU 23%96%
WordPress 2,342 sitesOver 1,200ms scripting CPU 47%450 to 1,200ms scripting CPU 28%150 to 450ms scripting CPU 17%96%
450 to 1,200ms scripting CPU Over 1,200ms scripting CPU 150 to 450ms scripting CPU Under 150ms scripting CPU
The State of Web Vitals · October 2026 · React: 9,570 crawled sites · 5,488 with phone field dataBy Arjen Karel · corewebvitals.io/state-of-cwv
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Main-thread CPU breakdown or the platform

Does the platform explain the main-thread CPU breakdown difference?

On Wix, 96% of sites with 450 to 1,200ms of scripting CPU main-thread CPU breakdown have a good INP, against 95% of Wix sites with over 1,200ms of scripting CPU. Within Wix, sites with 450 to 1,200ms of scripting CPU and over 1,200ms of scripting CPU have a good INP about equally often. On WordPress, 99% of sites with under 150ms of scripting CPU main-thread CPU breakdown have a good INP, against 99% of WordPress sites with 450 to 1,200ms of scripting CPU. Within WordPress, sites with under 150ms of scripting CPU and 450 to 1,200ms of scripting CPU have a good INP about equally often.

Why scripting dominates main-thread CPU budgets

Across the web, JavaScript evaluation accounts for the largest share of total main-thread CPU time, dwarfing HTML parsing, style calculation, and painting. Across 2,521 sites (26.3%) spending 150 to 450ms in scripting CPU, 94% pass field INP (79ms median), while the 30.5% (2,918) exceeding 1,200ms drop to 89% good INP (105ms median).

The State of Web Vitals · October 2026 · React: 9,570 crawled sites · 5,488 with phone field dataBy Arjen Karel · corewebvitals.io/state-of-cwv
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Understanding main-thread CPU breakdown

Audit scripts consuming over 450ms of CPU during boot and yield between hydration, analytics initialization, and DOM manipulation. Across all audited sites, 26.3% spend 150 to 450ms in scripting CPU (94% good INP, 79ms median) versus 30.5% above 1,200ms (89% good INP, 105ms median).

Go fix it Yield to the main thread → Fix excessive DOM size → JavaScript priority levels →
The State of Web Vitals · October 2026 · React: 9,570 crawled sites · 5,488 with phone field dataBy Arjen Karel · corewebvitals.io/state-of-cwv
Related signals Document lifecycle (lab) → Lab paint timeline → Total Blocking Time (lab) → By Arjen Karel · 9,570 crawled React sites (5,488 with phone Chrome field data, October 2026) · How we measured