Every 100 Milliseconds of LCP Costs About 3.5 Percent of Conversion

Shopify measured Core Web Vitals against conversion across its actively selling stores over 28 days and published the result in April 2026: every extra 100 milliseconds of Largest Contentful Paint tracked with roughly 3.5 percent lower conversion. Stores at a 2.5 second LCP converted about 30 percent lower than stores at 1.5 seconds. Cumulative Layout Shift showed no meaningful correlation with conversion at all.

The study, and why its size matters

Speed advice usually rests on one store's anecdote or a decade-old retail case study. This dataset is the platform itself: 28 days of Core Web Vitals and conversion data at the turn of January and February 2026, across actively selling Shopify stores in more than 175 countries, with the slowest 5 percent of stores excluded so a few broken sites would not drag the curve. The author was a Shopify performance engineer, and the write-up ran on Shopify's enterprise blog in April 2026.

The headline relationships are dose-shaped, not binary. LCP did not matter only past a cliff; each 100 millisecond step cost about the same. That is what makes the number usable for prioritization: you can price a 200 millisecond improvement before you build it.

INP counts, CLS does not, on this data

Interaction to Next Paint, the responsiveness metric that replaced First Input Delay in March 2024, also tracked with conversion: about 32 milliseconds slower INP corresponded to roughly 1.5 percent lower conversion. It is the smaller lever of the two, and it is the one app scripts tax hardest, since INP measures the worst lag between a tap and the page answering.

Cumulative Layout Shift is the surprise. Half the audits merchants receive lead with CLS because it is easy to measure and easy to fix. On Shopify's data it showed no meaningful correlation with conversion. CLS remains a Google ranking input and a trust issue when a button jumps mid-tap, but as a revenue lever on this evidence it is a dud, and audit hours spent there are hours not spent on LCP.

Turning the number into a decision

Pull the 75th percentile LCP for your top ten landing pages from the Core Web Vitals report in Search Console. That percentile is the standard Google and Shopify both judge by, and it describes the slow quarter of real visits, not your office connection. Flag every page over 2.5 seconds. On a store doing a million in annual revenue at a 2 percent conversion rate, the study's relationship prices a 200 millisecond LCP cut at roughly $14,000 a year, before any change in order value.

Then look at what the LCP element actually is on the flagged pages. On Shopify stores it is usually the hero or product image, which means the fix list is short: image sizing and format, preload discipline, and removing whatever script delays the paint. Measure each fix against the same percentile, not a single lab run.

What not to buy with this study

The study does not say speed is the only lever, and it does not license a rebuild. It says that within the range real stores occupy, LCP improvements pay at a roughly constant rate. A store already at 1.4 seconds gains little from chasing 1.2; the same effort at the checkout or on a confusing product page will pay more. Use the number to rank speed against your other work, not to crown it permanently.

Frequently asked questions

How much conversion does slow LCP cost a Shopify store?

On Shopify's platform-wide data, about 3.5 percent lower conversion for every extra 100 milliseconds of Largest Contentful Paint. Stores at 2.5 seconds LCP converted roughly 30 percent lower than stores at 1.5 seconds. The figures come from 28 days of data across actively selling stores, published in April 2026.

Does Cumulative Layout Shift hurt Shopify conversion?

Not measurably, in Shopify's study. CLS showed no meaningful correlation with conversion across the platform dataset. It still matters for Google's ranking thresholds and for basic trust when elements jump, but it should not lead a conversion audit ahead of LCP.

What is a good LCP for a Shopify store?

Google's threshold is 2.5 seconds or under at the 75th percentile of real visits, and Shopify's data shows the conversion cost accumulating well before that line. Treat 2.5 seconds as the ceiling, and price improvements below it using the roughly 3.5 percent per 100 milliseconds relationship.

Where do I find my store's real LCP?

In Google Search Console's Core Web Vitals report, which shows field data at the 75th percentile over 28 days, grouped by page type. Check your top landing and product pages there rather than relying on a single PageSpeed lab run from your own connection.