How to fix cwv lcp on BigCommerce
Reduce Largest Contentful Paint (LCP) to under 2.5 seconds by serving your hero image in a modern format, preloading it, and eliminating render-blocking resources.
Steps for BigCommerce
- Convert your hero/carousel images to WebP externally, then upload them via Storefront → Image Manager or directly through the Banner/Carousel editor (Marketing → Banners or Storefront → Home Page Carousel).
- In your Stencil theme files (Storefront → My Themes → Advanced → Download), open templates/components/carousel.html (or your hero partial). Change the <img> src to the WebP version and add fetchpriority='high' loading='eager' attributes.
- Add a preload hint: in templates/layout/base.html inside <head>, add <link rel='preload' as='image' href='{{cdn 'img/hero.webp'}}' fetchpriority='high'>.
- Remove lazy loading from the LCP image: ensure the hero <img> does NOT have loading='lazy'. BigCommerce's default Cornerstone theme lazy-loads below-fold images — confirm the hero is excluded.
- Defer render-blocking scripts: in base.html move third-party <script> tags to the bottom of <body> and add 'defer'. Use the BigCommerce Script Manager (Storefront → Script Manager) to set placement to 'Footer' and load strategy to 'Defer' for any injected scripts.
- Re-upload the modified theme and publish it; verify with PageSpeed Insights.
<link rel="preload" as="image" href="/images/hero-banner.webp" fetchpriority="high" imagesrcset="/images/hero-banner-800.webp 800w, /images/hero-banner-1500.webp 1500w" imagesizes="100vw">
<!-- Hero img tag — NO lazy loading, explicit dimensions -->
<img src="/images/hero-banner.webp"
srcset="/images/hero-banner-800.webp 800w, /images/hero-banner-1500.webp 1500w"
sizes="100vw"
width="1500" height="600"
alt="Descriptive hero text"
fetchpriority="high"
loading="eager">What is cwv lcp?
Largest Contentful Paint (LCP) measures how long it takes for the biggest visible element on your page — almost always the hero image or headline banner — to fully appear on the screen after someone clicks your link. Google considers anything under 2.5 seconds "Good," 2.5–4 seconds "Needs Improvement," and over 4 seconds "Poor." An LCP of 7.5 seconds on mobile means shoppers are staring at a blank or half-loaded page for over seven seconds before they see your store's main content — a painfully long wait that drives them away before they ever see your products.
LCP is one of Google's Core Web Vitals, a confirmed ranking signal that directly affects where your store appears in search results. A poor LCP score suppresses organic traffic, meaning fewer potential buyers even find your store. On mobile — where most ecommerce browsing now happens — slow LCP dramatically increases bounce rates: studies consistently show conversions drop 4–8% for every additional second of load time. Improving LCP from 7.5s to under 2.5s can meaningfully lift both your search rankings and the percentage of visitors who stay long enough to make a purchase. Mobile-first indexing means Google judges your site primarily by its mobile experience, so a slow mobile LCP hurts your desktop rankings too.
See the complete Cwv lcp guide for every platform and the full background.
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