How to fix low performance score on BigCommerce

Steps for BigCommerce

1. Use Cornerstone theme — Storefront → Themes: Cornerstone (BigCommerce's official theme) is the most performance-optimized. If on a custom theme, compare its PageSpeed score against Cornerstone to diagnose theme-level bloat.
2. Script Manager — Store Setup → Script Manager: review every script installed. Delete or disable scripts that are not actively used. Set non-critical scripts to 'Footer' placement and load strategy 'Defer' where the option exists.
3. Image optimization — When uploading product images, BigCommerce serves them via Akamai CDN automatically. Ensure you upload images no larger than necessary (max 1280 px on longest side for most layouts). Use WebP uploads where your theme supports the <picture> element.
4. Lazy loading — In Storefront → My Themes → Advanced → Edit Theme Files → templates/components/products/product-listing.html, add loading='lazy' to product card images.
5. Fonts & CSS — In assets/scss/settings/ reduce the number of loaded font weights and use font-display: swap in your SCSS files.
6. Apps — Apps Marketplace: 'Yottaa' or 'Amasty Speed Optimizer' provide server-side script bundling and CDN optimization for BigCommerce stores.

<!-- Hero/LCP image: load eagerly with high priority, explicit dimensions -->
<img
  src="hero-banner.webp"
  alt="Summer collection — shop now"
  width="1200"
  height="600"
  loading="eager"
  fetchpriority="high"
/>

<!-- All below-fold images: lazy-load, explicit dimensions to prevent CLS -->
<img
  src="product-thumbnail.webp"
  alt="Blue running shoes"
  width="400"
  height="400"
  loading="lazy"
/>

<!-- Defer non-critical third-party scripts -->
<script src="https://example-chat-widget.com/widget.js" defer></script>

What is low performance score?

Lighthouse (the engine behind Google's PageSpeed Insights tool) grades every page from 0–100 on performance. The score rolls up several real-world loading metrics — most importantly Google's Core Web Vitals: Largest Contentful Paint (LCP, how fast the main content appears), Interaction to Next Paint (INP, how fast the page reacts to taps/clicks), and Cumulative Layout Shift (CLS, how much the layout jumps around). A score of 8/100 on mobile means the page is extremely slow for the majority of shoppers who visit on a phone. The score is not a vanity number — it reflects a genuine, measurable delay that real visitors experience.

Google uses page experience signals, including Core Web Vitals, as a ranking factor for mobile search — a store with a very low score can lose meaningful search visibility to faster competitors. Beyond rankings, conversion research consistently shows that every additional second of load time can reduce conversions by 10–20%; a score in single digits means customers are likely abandoning the page before it even finishes loading. Slow pages also penalize your Google Ads Quality Score, raising your cost-per-click. On mobile — where most ecommerce traffic now originates — the experience gap between a score of 8 and 80 is the difference between a bounce and a sale.

See the complete Low performance score guide for every platform and the full background.