What Is the Impact of Custom Web Fonts on Largest Contentful Paint (LCP), and How Can I Ensure Faster Loading of Critical Fonts?


Custom web fonts can adversely affect the Largest Contentful Paint (LCP) performance, which measures the loading time of the largest content element visible in the viewport. Slow-loading web fonts can delay LCP, especially if the fonts are render-blocking. However, strategies like font optimization, preloading fonts, and using font-display properties can ensure faster loading of critical custom web fonts.

Impact of Custom Web Fonts on LCP

Custom web fonts have a significant impact on LCP. If these fonts are loaded late or are render-blocking, they can delay the paint of the largest content element, thereby increasing LCP time. With a poor LCP score, a website may offer a subpar user experience, as users tend to perceive slow websites as less reliable or less professional [Largest Contentful Paint (LCP), 2020].

Strategies for Faster Loading of Critical Custom Web Fonts

Font Optimization

Font optimization includes compressing font files, using modern font formats like WOFF2, and subsetting fonts to include only the necessary characters. These techniques can reduce the amount of data that needs to be loaded, speeding up font delivery [Web Font Optimization, Google Web Fundamentals].

Preloading Fonts

Preloading allows a browser to start downloading a resource as soon as possible. By using the <link rel="preload"> tag, you can instruct the browser to download key web fonts earlier, which helps to improve LCP [Preload Critical Assets, web.dev].

Font-Display Properties

The font-display CSS property determines how a font is displayed based on whether and when it is downloaded and ready to use. The `"font-display: swap;"` property value can be helpful as it ensures text remains visible to the user while custom fonts load [font-display - CSS: Cascading Style Sheets, MDN web docs].

Preconnect to Font CDN

Preconnect allows the browser to set up early connections before an HTTP request is actually sent to the server. This can be beneficial when using a web font from a third-party source. The <link rel="preconnect"> tag enables the browser to establish the connection to the font's source in advance, reducing the time it takes to fetch the font [Use rel=preconnect to establish network connections early and increase performance, web.dev].


Implementing these strategies to improve the loading time of custom web fonts can effectively enhance the LCP performance and overall user experience on your website.