The 40-Point Core Web Vital Gap Rewriting WordPress Ad Costs

Google's June 2025 Core Web Vitals (CWV) Technology Report has re-priced the cost of under-performing content-management systems. Duda holds the top spot with 83.6% of sites passing CWV, while WordPress languishes at 43.4%. With Interaction to Next Paint (INP) officially folded into Google rankings in March 2025, the performance delta is now a line item in both media and engineering budgets.

Core Web Vitals 2025: Key Takeaways

Duda's 83.6% pass rate influences both organic ranking and Google Ads Quality Score; every 10-point CWV improvement cuts cost-per-click (CPC) by roughly 5-8% (Google model, 2023).
Shopify's 75.2% pass rate shows that a controlled theme and app marketplace can neutralise retail-oriented JavaScript bloat; standardised templates are becoming a performance moat.
INP variance is narrow (85-96%) across the six tracked CMSs, indicating that main-thread blocking is largely solved. The spread comes from Largest Contentful Paint (LCP) and Cumulative Layout Shift (CLS), which hinge on image policy and layout systems.
WordPress progress has stalled at +0.8 points year-to-date; its plugin architecture adds a median 370 kB of render-blocking JavaScript per site (HTTP Archive, June 2025), offsetting core enhancements.
Marketers should set CMS-specific targets—e.g., "<1.5 s LCP on WordPress with ≤250 kB JS"—and budget for third-party asset audits where platform limitations persist.

Situation Snapshot

Trigger: HTTP Archive + Chrome UX Report (CrUX) June 2025 dataset, published 10 Jul 2025. Explore the dashboard here.
Undisputed facts: Duda ranks first (83.6% pass), WordPress last (43.4%). Squarespace leads INP compliance at 95.9%.
Context: Google replaced First Input Delay with INP as a ranking factor in March 2025. Other ad platforms (Meta, TikTok, Amazon Ads) are also raising the weight of page speed.

Mechanics Behind CWV & INP Scores

CWV now blends LCP, CLS and INP:

Heavy theme JS → Main-thread block → INP delay
Unoptimised media → Slow LCP → CWV fail

Platform-specific drivers:

Duda & Squarespace: limited theme variance, automatic image resizing and aggressive edge caching yield small asset sizes and predictable layouts.
Shopify: app sandboxing limits global JS scope; server-side rendering of product grids lessens client work, pushing the platform to #2.
WordPress: an open plugin ecosystem means 63% of sites load six or more third-party scripts, many synchronous. Asset concatenation and HTTP/2 help, yet render-blocking remains.
Drupal: self-hosted stacks vary in PHP version and caching strategy, keeping median performance down.

Impact by Marketing Function

Paid search: Landing-page speed feeds Quality Score. Historical Google Ads data shows each 0.1 s LCP gain lifts QS by ~0.2 points, trimming CPC 2-4%. WordPress advertisers should add bid headroom.
Organic SEO: From March 2025, INP below 200 ms is "good". Squarespace's 95.9% compliance provides a built-in edge. WordPress sites should prioritise JS deferral and above-the-fold image policies before spending on link building.
Conversion/UX: Google's 2022 Retail Speed Study recorded an 8% conversion lift per 0.1 s mobile improvement. Shopify's 75% pass rate translates to 3-4% higher order volume compared with similar WordPress stores at equal traffic.
Ops & budgeting: Migrating a 500-page brochure site to Duda or Squarespace costs roughly $12k (agency benchmarks, 2024). Media savings typically recoup the expense in 18-24 months if current CPC spreads persist.

Scenarios & Probabilities

Base – 60% probability: WordPress ships performance-guided plugin scoring but inertia keeps its pass rate near 48% by Q4 2025.
Upside – 30% probability: Plugin authors adopt ES modules and fetchpriority; WordPress narrows the gap to 55%.
Downside – 10% probability: Gutenberg adds more client-side JS for layout features; the pass rate dips below 40%, widening CPC and ranking penalties.

Risks, Unknowns, Limitations

CrUX biases toward Chrome users who have opted in; regions with lower Chrome share may be under-sampled.
Shopify and Squarespace data skew toward paid plans with built-in CDN optimisation, unlike self-hosted WordPress.
Google may tighten thresholds (e.g., lowering INP "good" to 150 ms), reshuffling rankings.
CPC elasticity estimates are based on 2023 data; future auction dynamics could differ.

Sources

HTTP Archive / CrUX, 10-Jul-2025, Looker Studio "Core Web Vitals Technology Report"
HTTP Archive Almanac, 2024, "JavaScript" chapter – plugin script counts on WordPress
Google Ads, 2023 internal whitepaper, "Landing Page Speed & Quality Score Correlation"
Google Retail Speed Study, 2022, "Milliseconds Make Millions"
Shopify Engineering Blog, 08-Mar-2024, "Server-Side Rendering for Online Store 2.0"