We Ran Lighthouse on Our Own 6 Shopify Stores. Not One Hit Google's LCP Target.

We build Shopify stores for a living, and we run six of our own. In September 2026 we ran Lighthouse on all six. The best mobile score was 85. The worst was 47. And not one store loaded its largest element inside Google’s 2.5-second target.

That’s not a confession for effect. It’s the most useful dataset we have for Shopify speed optimization, because it shows what happens to real stores, on a current theme, once products, languages and apps pile up. Every one of these stores launched in 2026 on Shopify’s Horizon theme. Every one of them got slower than the theme alone would be.

The short version: a slow Shopify store is almost never slow because of Shopify. It’s slow because of what was added on top: app scripts, heavy images above the fold, and interactive features that load on every page. Here’s what we measured, what we think caused it, and the order we now fix things in.

The numbers: one Lighthouse run on six real Shopify stores

Method, stated plainly: a single Lighthouse lab run per store, mobile profile, run locally in September 2026. One run is noisy; scores can move several points between runs. Treat these as approximate snapshots, not a benchmark.

Two more data points from the same run. Layout shift (CLS) was 0.03 or lower on all six stores, well inside the 0.1 limit. And mamawszoku.pl logged 1.15 seconds of JavaScript blocking time, the heaviest of the group.

For reference, web.dev defines the Core Web Vitals thresholds as LCP of 2.5 seconds or less, INP of 200 milliseconds or less, and CLS of 0.1 or less, measured at the 75th percentile of real page loads.

What the Lighthouse run tells us (and what it doesn’t)

Layout shift is solved; loading isn’t

CLS near zero on every store says the theme and our image sizing are doing their job. Nothing jumps around as the page loads. That’s the part a modern Shopify theme gets right out of the box, and we didn’t break it.

LCP is a different story. The fastest store took 3.9 seconds to paint its largest element in the lab. The slowest two took 7.1 seconds. On a phone, that’s the difference between seeing the product and seeing a blank hero.

The slowest store is the one doing the most

mamawszoku.pl scored lowest and blocked the main thread longest. It’s also the store with the most going on: Booksy booking, a jewelry set builder, gift vouchers, and 1,229 products. We haven’t isolated each script yet, so treat this as a working hypothesis, not a finding: interactive features are the likely cost.

limewash.pl ties it on LCP at 7.1 seconds. It sells by color, with 182 shades, testers and a material calculator. Color-heavy pages lean on large imagery, and that’s where we’re looking first.

The best score still missed the target

Our top scorer, one of our newer stores, reached 85 and still needed 3.9 seconds for LCP. That’s the uncomfortable middle: a score that looks fine on a dashboard, and a phone user still staring at a half-loaded hero. It fits the pattern every speed guide describes, and now we’ve seen it in our own admin: stores don’t launch slow, they get slow.

What Lighthouse can’t tell you

Lighthouse is a lab test on a simulated mid-range phone and a throttled connection. Google ranks on field data: real visitors, over 28 days. Your store can score 60 in the lab and still pass Core Web Vitals in the field if your buyers use fast phones on good networks, or the reverse. Use Lighthouse to find problems; use field data to decide whether you’ve fixed them.

That’s the part most speed articles skip. The lab score is a debugging tool, not a grade.

Why Shopify stores get slow: the four usual causes

Across our own stores and the stores we audit, the same four causes come up, in roughly this order of impact.

1. App scripts that load everywhere

A reviews widget shows on the product page but often loads its script on the homepage, collections and cart too. Multiply that by a chat bubble, a pop-up, a loyalty widget and two tracking pixels. Shopify takes this seriously enough that its Built for Shopify requirements say an app must not reduce the storefront Lighthouse performance score by more than ten points. That’s a ceiling for one app, not a budget, and a store with five apps can spend it five times.

2. The hero image is the LCP element, and it’s too heavy

On most Shopify templates, the largest element is the hero banner on the homepage and the first product image on product pages. If that image is huge, lazy-loaded by mistake, or behind a slideshow script, LCP suffers. The fix is usually boring: right-size it, don’t lazy-load the first image, and skip auto-rotating slideshows above the fold.

3. Third-party tags added by marketing

Pixels, heatmaps, A/B testing snippets, affiliate scripts. Each one is small. Together they compete with your product image for the phone’s attention. Audit them twice a year; half are usually from a campaign that ended.

4. Fonts and theme customizations

Three font families, each in four weights, plus custom code pasted into theme.liquid years ago. Rarely the biggest issue on its own, often the thing that turns “moderate” into “poor.”

Shopify speed optimization: the fix order we follow

Here’s the sequence we use on our own stores and on client stores. It’s ordered by impact per hour, not by what’s most fun to fix.

1. Get field data first. Check Shopify’s web performance report (Analytics > Reports, search “Web performance”) and the Core Web Vitals report in Search Console. According to Shopify’s help docs, it shows loading, interactivity and visual stability over time. If field data already passes, prioritize differently.
2. Inventory every app and tag. List what each one costs in scripts and what it earns. Remove what nobody can justify.
3. Fix the LCP element on home, collection and product templates. Image size, format, loading priority.
4. Scope app scripts to the templates that use them. Many apps offer app embeds you can switch off per template; some need theme edits.
5. Defer non-critical third-party scripts. Chat and pop-ups can wait until after the product is visible.
6. Trim fonts and dead theme code.
7. Re-measure in the lab, then wait 28 days for field data.

Work on a duplicate theme, never the live one. Publish only after the before/after numbers are in.

Lab note

These six stores went live between January and July 2026, all on Horizon, all built by us. If our own stores collected this much speed debt in months, a store that’s been adding apps since 2019 almost certainly has more. We’re working through that fix order on our own stores now.

Shopify page speed quick wins you can check today

Not every fix needs a developer. These take under an hour and often show up in the next lab run:

• Turn off app embeds you don’t use. In the theme editor, open App embeds and switch off anything tied to an app you’ve stopped using. Uninstalled apps sometimes leave these behind.
• Replace an autoplay slideshow at the top of the homepage with one strong image.
• Check the first product image size. If the file is several megabytes, re-export it before uploading.
• Remove a font weight or two in theme settings if your theme lets you pick them.
• Delete tracking pixels from campaigns that ended.

None of this is a full Shopify speed optimization project. It’s the housekeeping that stops the next one from being bigger.

How fast does a Shopify store need to be?

Fast enough to pass Core Web Vitals in field data on mobile, on your key templates: home, collection, product, cart. That’s the bar that matters to Google and roughly the bar where speed stops being the reason people leave.

Chasing a 100 Lighthouse score on a store with reviews, subscriptions and live chat is a waste of money. Chasing “LCP under 2.5 seconds for real visitors on product pages” is not.

The honest takeaway

Speed isn’t a launch task. It’s maintenance. Every app you add is a small tax, and the bill arrives quietly as a slower product page six months later.

If you want to know what your store’s bill looks like, start with a free Store Scan: we check mobile Core Web Vitals on your home, collection and product pages and tell you what slows them, in plain words. If you already know it’s slow, our Speed Audit is $490 and credited in full to a Speed Fix. The Speed Fix is $1,490, done on a duplicate theme, with a pass-mobile-Core-Web-Vitals-or-partial-refund guarantee. And if you’re about to install another app, read our list of apps we’d install on day one first.