Main-thread CPU breakdown and the Core Web Vitals
26.9% of audited sites (55,913) spend over 1,200ms in main-thread scripting during load, pushing median field INP to 95ms (94% good INP) versus 83ms (96% good INP) at 150 to 450ms.
23.5% of sites use 150 to 450ms of scripting CPU main-thread CPU breakdown, and 96% of those sites have a good INP, against 95% of all sites.
INP pass rate
Sites with 150 to 450ms of scripting CPU main-thread CPU breakdown have a good INP most often: 96%, against 95% of all sites. Sites with under 150ms of scripting CPU scripting CPU have it least often, at 93%.
Main-thread CPU breakdown usage
Over 1,200ms of scripting CPU is the most used: 26.9% of sites. 150 to 450ms of scripting CPU is 23.5% of sites.
Understanding main-thread CPU breakdown
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 48,796 sites (23.5%) spending 150 to 450ms in scripting CPU, 96% pass field INP (83ms median), while the 26.9% (55,913) exceeding 1,200ms drop to 94% good INP (95ms median).
Audit scripts consuming over 450ms of CPU during boot and yield between hydration, analytics initialization, and DOM manipulation. Across all audited sites, 23.5% spend 150 to 450ms in scripting CPU (96% good INP, 83ms median) versus 26.9% above 1,200ms (94% good INP, 95ms median).
How main-thread CPU breakdown plays out per platform
What the field data shows when you isolate a single CMS or framework.
WordPress 65,939 sites 36% of WordPress sites spend over 1.2 seconds in scripting CPU during load.
Across WordPress sites, 36% spend over 1,200ms in main-thread scripting during boot (92ms median field INP, 98% pass rate), compared with 77ms median INP on the 14% under 150ms.
Shopify 8,634 sites 47% of Shopify stores exceed 1.2s of scripting CPU, passing INP 6 points less often than stores at 150 to 450ms.
Across Shopify storefronts, 47% spend over 1,200ms in main-thread scripting CPU (93% field INP pass rate, 112ms median) compared with 99% (79ms median) at 150 to 450ms.
React 9,658 sites 69% of React sites spend over 450ms in scripting CPU.
Across React sites, 39% spend 450 to 1,200ms in scripting CPU (96% INP pass rate, 79ms median) and 31% exceed 1,200ms (94%, 91ms median), compared with 96% (72ms median) at 150 to 450ms.
Wix 5,873 sites 75% of Wix sites sit between 150ms and 1,200ms of main-thread scripting CPU.
Across Wix sites, 44% spend 450 to 1,200ms in scripting CPU (98% INP pass rate, 74ms median) and 31% spend 150 to 450ms (98%, 70ms median).
By Arjen Karel · 212,308 crawled sites (197,524 with all devices Chrome field data, 207,664 sites with main-thread CPU breakdown, October 2026). How we measured.