What does "below the fold" mean?

Images below the fold are not visible on the initial viewport without scrolling. These are the prime candidates for lazy loading because they do not need to load immediately.

How accurate is the LCP estimate?

The LCP figure is a rough approximation based on 100 ms per 100 KB saved on a typical 3G connection (about 1.5 Mbps). Actual improvement varies by network speed, image format, CDN, and which specific image is the LCP element.

What percentage of users never scroll?

Studies suggest 40-60% of users on many pages never reach the bottom. The default of 40% is a conservative estimate. Adjust it based on your analytics scroll depth data.

Does lazy loading affect SEO?

Modern lazy loading using the native loading="lazy" attribute is fully supported by Google's crawler. Images important for SEO (like hero or product images) should not be lazy loaded.

Lazy Load Savings Calculator

Estimate how many KB/MB lazy loading saves on initial page load based on your image count, size, and user scroll behavior.

Page Image Settings

Adjust the values to match your page.

Total images on page

Average image size (KB)

Images below the fold 70%

0%100%

Users who never scroll to bottom 40%

0%100%

Results

Total payload (before)

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Bytes saved (lazy load)

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Savings percentage

—

Images never loaded

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Summary

Calculate the initial payload reduction from lazy loading images. Enter your total image count, average size, and scroll behavior estimates to see bytes saved and projected LCP improvement.

How it works

Total payload is computed as image count multiplied by average image size.
Below-the-fold image count is total images times the below-fold percentage.
Never-loaded images equals below-fold count times the never-scroll percentage.
Bytes saved equals never-loaded images times average image size.
LCP improvement is estimated at roughly 100 ms per 100 KB saved on a 3G connection.

Use cases

Justify adding lazy loading to a content-heavy blog or news site.
Estimate performance gains before implementing lazy loading in a web app.
Quickly compare lazy load impact across different page layouts.
Support a Core Web Vitals improvement proposal with concrete numbers.

Frequently Asked Questions

Last updated: 2026-06-19 · Reviewed by Nham Vu