App Speed Report · Updated February 2026

Does Klaviyo Slow Down Your Shopify Store?

Speed impact analysis of Klaviyo (Email & SMS Marketing) — how much it affects your page load time, what scripts it loads, and how to mitigate the performance cost.

Klaviyo Speed Impact Summary

Speed Impact Level High Impact

Scripts Loaded

220KB

Total Script Size

200-400ms

Avg. Load Time Impact

App Name

Klaviyo

How Klaviyo Affects Your Store Speed

Klaviyo is the leading email and SMS marketing platform for Shopify stores, powering signup forms, popups, flyouts, and on-site tracking for behavioral segmentation.

When a visitor lands on your store, Klaviyo loads 4 JavaScript files totaling approximately 220KB. These scripts need to be downloaded, parsed, and executed by the browser — all of which takes time and competes with your core page content for network bandwidth and CPU resources.

The measured impact is 200-400ms of additional page load time. To put that in perspective: Google research shows that each additional 100ms of load time reduces conversion rates by up to 7%. If Klaviyo adds 200-400ms to your page load, that's a measurable impact on your bottom line.

As a high-impact app, Klaviyo is likely one of the top speed offenders on your store. This doesn't mean you should uninstall it — email & sms marketing functionality is important — but you should prioritize optimizing how it loads.

What These Scripts Do

Klaviyo's scripts handle its core email & sms marketing functionality on your storefront. This typically includes:

• Core functionality script — The main JavaScript bundle that powers Klaviyo's features on your pages
• Tracking/analytics script — Monitors user interactions and behavior for Klaviyo's dashboard and reporting
• UI/widget scripts — Renders visual elements like popups, widgets, or embedded components on your storefront

The problem isn't that these scripts exist — it's that they often load synchronously and on every page, even pages where Klaviyo's functionality isn't needed. A visitor browsing your blog doesn't need Klaviyo's full email & sms marketing scripts loading and executing.

How to Reduce Klaviyo's Speed Impact

You don't have to choose between Klaviyo's functionality and a fast store. Here's how to minimize its performance impact while keeping the features you need:

Defer Klaviyo's identify and tracking scripts until after page load completes — they don't need to run immediately

Disable Klaviyo's on-site popup on pages where you don't need it (e.g., checkout, cart) to prevent loading popup JS/CSS

Use Klaviyo's built-in 'delay popup display' setting — this doesn't help speed directly but reduces perceived slowness

If you only use Klaviyo for email (no on-site forms), consider removing the on-site JS snippet entirely and relying on embedded forms

Move Klaviyo's tracking pixel to load after the DOMContentLoaded event instead of in the head

Consolidate Klaviyo forms — each active form type (popup, flyout, embedded) loads additional CSS and JavaScript

🔍 SEO impact: Reducing Klaviyo's speed impact helps your store pass Core Web Vitals — Google's official ranking signal since 2021. Better speed = higher rankings = more organic traffic.

The Bigger Picture: App Bloat on Shopify

Klaviyo is just one app on your store. The average Shopify store has 15-25 apps installed, and each one adds its own JavaScript and CSS to your storefront. The cumulative effect is what really kills your speed score.

Think about it: if Klaviyo adds 200-400ms and you have 10+ other apps each adding 100-400ms, your total third-party script overhead could be 2-5 seconds. That's the difference between a store that converts and one that loses visitors before the page even loads.

Manually optimizing each app's loading behavior is time-consuming and requires technical knowledge. You'd need to edit theme files, understand JavaScript loading patterns, and constantly monitor for regressions when apps update their scripts.

This is exactly the problem Thunder was built to solve. Thunder automatically scans every app on your store, measures each one's actual speed impact (including Klaviyo), and optimizes how they all load — deferring non-essential scripts, reducing blocking time, and ensuring your critical page content loads first.

⚡ See How Klaviyo Affects Your Store

Thunder scans your installed apps — including Klaviyo — and shows you exactly how much each one impacts your speed. Then it fixes them automatically.

Install Thunder Free →

Free plan available · Scans all your apps · No code changes required

Frequently Asked Questions

Does Klaviyo slow down Shopify stores?

Klaviyo has a high speed impact on Shopify stores, typically adding 200-400ms to page load time. It loads 4 scripts totaling approximately 220KB. While this isn't negligible, you can mitigate the impact by deferring its scripts, limiting which pages it loads on, and using a speed optimization app like Thunder to manage its loading behavior.

How much does Klaviyo affect my PageSpeed score?

Klaviyo typically reduces your PageSpeed Insights mobile score by 3-15 points depending on your store's baseline performance and other installed apps. The 220KB of JavaScript it loads contributes to longer Time to Interactive (TTI) and potentially affects Largest Contentful Paint (LCP) if scripts block rendering. The actual impact varies — stores with fewer apps will notice it more.

Should I uninstall Klaviyo to improve speed?

Not necessarily. Klaviyo provides valuable functionality (email & sms marketing) that likely benefits your store. Instead of uninstalling, optimize how it loads: defer non-critical scripts, limit it to pages where it's needed, and use Thunder to automatically manage its loading priority. Only uninstall if you're not actively using the app or if the speed cost outweighs the business value.

Can I use Klaviyo and still have a fast Shopify store?

Yes. Many high-performing Shopify stores use Klaviyo successfully. The key is optimization: don't load Klaviyo's scripts on pages where they're not needed, compress your images to offset the script overhead, and use a tool like Thunder to defer Klaviyo's JavaScript until after your critical content has loaded. A well-optimized store with Klaviyo can still score 80+ on PageSpeed mobile.