87.3% of websites that show their Bootstrap version run Bootstrap 4 or older, versions that no longer receive fixes. Bootstrap 3, unsupported since July 2019, is still the most common version, on 1,001,551 homepages.
Analysis of 2,184,137 homepages with a readable Bootstrap version · the public HTTP Archive crawl of 15.5 million websites, September 2026
Key Findings
- 1.87.3% of websites that show their Bootstrap version run Bootstrap 4 or older, versions that no longer receive fixes, against 12.7% on the supported Bootstrap 5.
- 2.Bootstrap 3, unsupported since July 2019, still runs on 45.9% of websites that show their Bootstrap version, 1,001,551 homepages.
- 3.Bootstrap 4, unsupported since January 2023, runs on 39.5% of websites that show their Bootstrap version, 861,771 homepages.
- 4.The 10,000 most visited websites run unsupported Bootstrap 86.8% of the time, almost the same as the 87.5% of websites outside the top 10 million.
- 5.Unsupported Bootstrap runs on 12.3% of all 15.5 million website homepages, and 42,495 homepages still load Bootstrap 2 or older.
Summary
A business launched its website in 2017 on a Bootstrap 3 theme. The site still looks fine, the menus open and the forms send. But the framework under it stopped receiving fixes in July 2019, and the jQuery version it depends on has known security flaws. Nobody has touched the front end since launch, because nothing looked broken.
Bootstrap is a framework, a package of ready-made design and code, that websites use for layouts, menus, buttons, pop-ups and sliders. It is one of the most widely used front-end tools on the web. Like any software, each major version gets fixes for a set period and then reaches end of life, the point where its developers stop releasing updates, including security fixes.
Almost nine in ten websites that show their Bootstrap version are past that point. 87.3% run Bootstrap 4 or older, and Bootstrap 3, unsupported for seven years, is still the single most common version at 45.9%. Only 12.7% run the supported Bootstrap 5. Unlike most maintenance problems, this one barely changes with site size: the most visited websites are almost exactly as likely to run old Bootstrap as the smallest.
What we measured
We used the public HTTP Archive crawl of September 2026, which records the Bootstrap version loaded on each website homepage where the version can be read. 2,184,137 homepages load Bootstrap and show which version. We counted those on a major version below 5 and grouped websites by popularity using Google's Chrome UX Report.
A Bootstrap version is unsupported when its developers no longer release fixes for it. Bootstrap 3 reached end of life in July 2019 and Bootstrap 4 in January 2023, so both count as unsupported, along with Bootstrap 2 and older. Bootstrap 5 is the supported version. "The top 10,000" are the 10,000 most visited websites in Chrome's ranking.
Bootstrap 3 is still the most common version
More websites run Bootstrap 3 than Bootstrap 4, and both far outnumber Bootstrap 5. Bootstrap 3 runs on 1,001,551 homepages and Bootstrap 4 on 861,771, against 278,320 on Bootstrap 5. A further 42,495 homepages load Bootstrap 2 or older.
Source: Suff Digital analysis of 2,184,137 homepages with a readable Bootstrap version · the public HTTP Archive crawl of 15.5 million websites, September 2026
The reason so many sites stay behind is the size of the upgrade. Moving from Bootstrap 3 or 4 to Bootstrap 5 changes the names of the building blocks a site's pages use and drops jQuery entirely, so every template and every custom script has to be checked. It is closer to a front-end rebuild than an update, and most owners put it off until their next redesign.
The most visited websites are just as far behind
For most maintenance problems, large websites with bigger teams do better. Bootstrap is the exception. The share of websites running unsupported Bootstrap sits between 83.8% and 87.5% at every level of popularity, and the 10,000 most visited websites are at 86.8%.
Source: Suff Digital analysis of 2,184,137 homepages with a readable Bootstrap version · the public HTTP Archive crawl of 15.5 million websites, September 2026
That flat line shows the problem is not a lack of resources. Popular websites carry years of templates built on Bootstrap 3 or 4, and rebuilding them costs more the bigger the site is. Small websites, meanwhile, often run on a theme that was built on an older Bootstrap and never updated by its developer.
The risk sits in the JavaScript
The danger in old Bootstrap is its JavaScript components, the code behind pop-ups, dropdown menus, tooltips and sliders, and the jQuery they depend on. Bootstrap 3 and 4 both require jQuery, and in a separate Suff Digital study, 36.1% of websites that show their jQuery version run one with known security flaws. A site on old Bootstrap is likely to be carrying old jQuery with it.
Unsupported Bootstrap runs on 12.3% of all 15.5 million website homepages, a large share of the web whose front end has not been rebuilt in years. Each of those sites depends on code that will not be fixed if a new flaw is found.
What this means for site owners and developers
Check which Bootstrap version your site loads: a free online scanner that lists JavaScript libraries will show it, or your developer can check the theme files. If it is Bootstrap 3 or 4, make sure the jQuery your site loads is 3.5.0 or newer, which closes the best-known flaws while you plan the larger upgrade.
Next, reduce what you load. Remove Bootstrap JavaScript components your pages do not use, and start testing with the pages that carry forms, menus and sliders, since those rely most on Bootstrap's JavaScript.
Then put the move to Bootstrap 5, or to a modern theme that uses it, on the plan for your next rebuild, and treat it as part of the project rather than an afterthought. Our website redesign services rebuild older front ends on current, supported frameworks without losing the pages and rankings a site already has.
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<p style="font:14px/1.5 system-ui,sans-serif">Source: <a href="https://www.suffdigital.com/resources/data-studies/outdated-bootstrap-websites">87.3% of Websites Using Bootstrap Run a Version That No Longer Gets Updates - Suff Digital</a></p>
Cite this study
Suff Digital. (2026). 87.3% of Websites Using Bootstrap Run a Version That No Longer Gets Updates. https://www.suffdigital.com/resources/data-studies/outdated-bootstrap-websites
87.3% of Websites Using Bootstrap Run a Version That No Longer Gets Updates - Suff Digital - https://www.suffdigital.com/resources/data-studies/outdated-bootstrap-websites
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