---
title: "Lighthouse 13.6 Stops Penalising Some Preloads in Simulated FCP and LCP"
description: "Lighthouse 13.6.0 stops counting module preloads and some fonts against simulated FCP and LCP. What changes in PageSpeed Insights, and what to re-test."
tldr: "Lighthouse, the Chrome lab tool behind the PageSpeed Insights performance score, estimates load times on a slow phone by simulation, and from version 13.6.0 (27 October 2026) that estimate stops counting some preloads against First Contentful Paint and Largest Contentful Paint. Module scripts and fonts that Chrome reports as non-blocking no longer delay simulated FCP, and a text LCP painted with FCP now gets the same time. The text fix does not cover image LCP."
publishDate: 2026-10-30
author: "Liam Hayward"
---
Lighthouse 13.6.0, released on 27 October 2026, changes how its default simulated throttling estimates First Contentful Paint (FCP) and Largest Contentful Paint (LCP). Simulated throttling loads the page on a fast connection and then calculates how it would have loaded on a slow mobile one, and until this release that calculation counted resources loaded early against both metrics whether or not the page waited for them. The release notes expect it to reach PageSpeed Insights within a week and the DevTools of Chrome 159, and do not say how much scores will move.

## What changed in Lighthouse's simulated FCP and LCP?

Two fixes matter for pages that preload. For FCP, Lighthouse treated every high-priority script, including `<script type="module">` and `<link rel="modulepreload">`, and every very-high-priority font as render-blocking; it now checks Chrome's own record of whether each request blocked rendering. For LCP, when the largest element is text painted in the same frame as FCP, simulated LCP now depends on the same resources as FCP, where before any font, image, async stylesheet or non-blocking script that finished downloading first pushed it later. Ivan Akulov, a performance engineer at the website builder Framer, reported the problem in June 2025 as "Lighthouse Punishes Good Asset Preloading", using a page whose real FCP and LCP were around 1.0 to 1.1 seconds and which scored yellow or red for FCP in PageSpeed Insights.

<figure>
  <picture>
    <source media="(max-width: 767px)" srcset="/images/news/lighthouse-13-6-simulated-lcp-preloads/lighthouse-13-6-waterfall-mobile.webp" width="400" height="1021" />
    <img src="/images/news/lighthouse-13-6-simulated-lcp-preloads/lighthouse-13-6-waterfall.webp" alt="Two panels showing the same four requests as bars on a time axis: HTML, a stylesheet, a module script and a font preload. Before Lighthouse 13.6, all four are counted, the FCP marker sits at the end of the module script and the LCP marker at the end of the font. From Lighthouse 13.6, the module script and font are drawn faded as not counted, and a single FCP equals LCP marker sits at the end of the stylesheet." width="768" height="812" loading="lazy" />
  </picture>
  <figcaption>A simplified model, not to scale, of a page whose largest element is a headline in a system font, as Lighthouse simulates it. Where the largest element is an image, files that finish downloading before it paints still count.</figcaption>
</figure>

## What to re-test after Lighthouse 13.6

If you removed modulepreloads or font preloads to raise a Lighthouse score, re-run the page on 13.6 before leaving them out, because a preload that made real visits faster no longer has to cost you in the lab. The text fix does not extend to image LCP: requests that finish before an image paints still count towards its simulated time. If a Performance score moves in early November on a page that has not changed, check which Lighthouse version produced the report before looking for a cause on the site. The lab score is not what Google Search measures: Google describes Core Web Vitals as metrics that "measure real-world user experience", and Search Console's Core Web Vitals report is based on field data from real visits, so a score that moves for this reason changes the diagnosis, not the page's standing in Search.

## Sources

- [Lighthouse v13.6.0 release notes, GitHub](https://github.com/GoogleChrome/lighthouse/releases/tag/v13.6.0)
- [Lighthouse Punishes Good Asset Preloading, issue #16539, GitHub](https://github.com/GoogleChrome/lighthouse/issues/16539)
- [trace_engine 0.0.66: render-blocking status from Chrome, pull request #17307, GitHub](https://github.com/GoogleChrome/lighthouse/pull/17307)
- [trace_engine 0.0.67: text LCP in the same frame as FCP, pull request #17379, GitHub](https://github.com/GoogleChrome/lighthouse/pull/17379)
- [Understanding Core Web Vitals and Google search results, Google Search Central](https://developers.google.com/search/docs/appearance/core-web-vitals)
- [Core Web Vitals report, Search Console Help](https://support.google.com/webmasters/answer/9205520)