How I Improved a Shopify Store’s Performance from 30% to 65% - GTmetrix

A Real Shopify Performance Optimization Journey When we upgraded our Shopify store to a new theme, I expected the performance to improve automatically. Instead, the first performance test showed something alarming. The store scored only 30% on GTmetrix — exactly the same as the old theme. Despite migrating to a new theme, the website was still slow. That moment started a deep investigation into Shopify performance optimization, Core Web Vitals, third-party scripts, and browser rendering behavior. What You'll Learn In this article I’ll cover: -> Investigating slow Shopify performance -> Optimizing Largest Contentful Paint (LCP) -> Reducing Total Blocking Time (TBT) -> Handling third-party scripts efficiently -> Fixing layout shifts (CLS) Over several weeks of experimentation, debugging, and testing, the store’s performance improved from 30% to 62%. This article documents that journey. Understanding the Performance Problem Modern website performance is heavily influenced by Core Web Vita