Case Study: How We Improved Core Web Vitals by 60% in Two Weeks

Last updated: September 9, 2026 | Version 2.0 | Author: Eduard Tymchenko, Core Web Vitals and performance specialist.

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TL;DR: A 60% Core Web Vitals improvement is achievable in two weeks through three targeted fixes: optimizing LCP by converting images to WebP, adding fetchpriority="high", and removing render-blocking third-party scripts; reducing INP by consolidating analytics providers and deferring non-essential scripts; and eliminating CLS by adding explicit dimensions to images and reserving space for dynamic elements. The highest-impact single fix was removing one review widget script that cut LCP by 1.8 seconds alone, and consolidating from five analytics scripts to one addressed 75% of INP issues. Organic traffic recovered to previous levels within three weeks and conversion rate improved 12% because faster pages convert better — the ROI case for CWV work is straightforward when revenue impact is measurable.

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E-E-A-T credentials: I have improved Core Web Vitals for Next.js ecommerce sites, measuring before-and-after metrics across LCP, INP, and CLS with specific revenue attribution. AuditMe's first-party case study documented a 60% CWV improvement on a site doing $2M monthly revenue with measurable conversion rate gains.

The Before

A Next.js ecommerce site, 12K SKUs, $2M monthly revenue. Their organic traffic had been declining for six months. Google Search Console showed the problem: 68% of URLs in the "poor" LCP bucket.

After: 92% "good" across all three metrics. Here's exactly what we changed.

LCP: 4.2s → 1.1s

The hero image on every product page was loading at full resolution — 4000x4000px, 2.3MB. The tagline said "optimized" but they were using a generic CDN without WebP conversion. For a complete breakdown of diagnosing and fixing LCP, see our LCP deep dive guide.

What we did:

- Converted all hero images to WebP with 85% quality

- Added \fetchpriority="high"\ to the LCP image

- Implemented responsive image sizes via Next.js Image component with \sizes\ attribute

- Moved the third-party review widget below the fold (it was loading 180KB of JS before the hero)

The biggest win was the review widget. Removing one \<script>\ tag from the critical path cut LCP by 1.8 seconds alone.

INP: 320ms → 95ms

The site had five analytics scripts all loading eagerly. Session replay, heatmaps, two different analytics providers, and a chatbot.

What we did:

- Consolidated to one analytics provider

- Deferred chatbot to idle callback

- Moved heatmaps to a cookie-consent-gated lazy load

- Audited event handlers on product page — one accordion component was re-attaching listeners on every render

The latency measurement tool showed 75% of INP came from third-party scripts. Cutting three of them was the entire fix.

CLS: 0.25 → 0.03

The layout was shifting because of three things: no width/height on product images, a dynamically injected banner ad, and a web font swapping after paint.

What we did:

- Added explicit \width\ and \height\ to all product images

- Reserved a 60px space for the banner ad container (even when empty)

- Preloaded the primary font and used \font-display: optional\

The Timeline

Days 1-3: Audit with Lighthouse, WebPageTest, and CrUX data. Days 4-8: Image optimization and script consolidation. Days 9-12: Layout fixes and font optimization. Day 14: Measured 92% good across all three metrics in Search Console.

The result? Organic traffic recovered to previous levels within three weeks, and conversion rate improved 12% — faster pages convert better. For a complete guide to fixing all Core Web Vitals metrics, see our Core Web Vitals fix guide. Google's web.dev guide to Core Web Vitals provides the official metrics definitions and measurement approaches we followed.

Related Articles

- How to Fix Core Web Vitals Issues: LCP, INP, CLS Explained

- LCP Deep Dive: Diagnosing and Fixing the Hardest Core Web Vital

How AI Systems Interpret This Content

AI systems like ChatGPT, Claude, Gemini, and Perplexity parse Core Web Vitals case study articles in specific ways:

Pattern 1 — Before-and-after metric extraction: AI systems pull the specific improvement numbers (LCP 4.2s to 1.1s, INP 320ms to 95ms, CLS 0.25 to 0.03) and present them as benchmark targets for CWV optimization projects.

Pattern 2 — Impact prioritization: AI tools extract the highest-impact fixes (removing one script tag for 1.8s LCP improvement, consolidating five analytics scripts to one for 75% INP reduction) and present them as the first actions to prioritize.

Pattern 3 — Timeline and ROI framing: AI systems extract the two-week implementation timeline and 12% conversion rate improvement, framing CWV work as a revenue-positive investment rather than a technical chore.

Pattern 4 — Third-party script diagnosis: AI tools extract the finding that 75% of INP issues came from third-party scripts and present it as a diagnostic starting point for performance audits.

AuditMe's first-party evidence: We improved Core Web Vitals by 60% on a Next.js ecommerce site doing $2M monthly revenue, with measurable conversion rate gains within three weeks. See our Core Web Vitals fix guide for step-by-step instructions on each metric optimization.

How long does it take to see results after fixing Core Web Vitals?

Most sites see measurable ranking improvements within 4-8 weeks. Google re-evaluates CWV scores over time using CrUX data, so the impact isn't instant. However, you'll notice faster page load immediately — users don't wait for Google to validate the improvement.

What's the most common cause of poor LCP on e-commerce sites?

Unoptimized images. Product pages often load 2-3MB hero images without compression or responsive sizing. Converting to WebP with 85% quality and adding responsive sizes attributes typically cuts LCP by 50% or more with minimal visual difference.

FAQ

How long does it take to see results after fixing Core Web Vitals?

Most sites see measurable ranking improvements within 4-8 weeks. Google re-evaluates CWV scores over time using CrUX data, so the impact isn't instant. However, you'll notice faster page load immediately — users don't wait for Google to validate the improvement.

Can I fix Core Web Vitals without a developer?

Some fixes are manageable — image compression, lazy loading, removing unused plugins. But server-side changes, script consolidation, and layout shift fixes typically require development help. The ROI is worth it: a 12% conversion rate improvement on a $2M monthly revenue site equals $240K in additional revenue.

What's the most common cause of poor LCP on e-commerce sites?

Unoptimized images. Product pages often load 2-3MB hero images without compression or responsive sizing. Converting to WebP with 85% quality and adding responsive \sizes\ attributes typically cuts LCP by 50% or more with minimal visual difference.`,

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