Using custom fonts can slightly affect your app's frame rate and memory. Loading fonts requires extra memory, but Flutter caches fonts efficiently after the first use. If you use many font weights or styles, memory use grows. Rendering text with custom fonts is usually smooth, but very large font files might slow down initial screen rendering.
Choose only the font weights and styles you need to reduce memory use. Use font subsetting tools to remove unused characters and reduce file size. Load fonts asynchronously if possible to avoid blocking UI. Cache fonts properly so they don't reload on every screen. Avoid switching fonts frequently during animations to keep smooth frame rates.
Custom fonts add to your app bundle size. A typical font file can be 100-500KB or more. Including many fonts or weights increases size and can slow app startup. To keep startup fast, include only necessary fonts and use compressed font formats like TTF or WOFF2. Flutter bundles fonts inside the app, so smaller fonts mean faster installs and updates.
On iOS, custom fonts are bundled in the app and registered via Info.plist. Flutter handles this automatically when you declare fonts in pubspec.yaml. Android bundles fonts in assets and uses font resources. Android supports downloadable fonts, but Flutter apps usually bundle fonts directly. Font rendering may differ slightly between platforms due to system text engines, so test appearance on both.
Loading too many or very large custom font files at startup can delay screen rendering. You might be including unnecessary font weights or styles. Also, fonts might be blocking the UI thread if loaded synchronously. Check your pubspec.yaml to include only needed fonts and consider lazy loading fonts after the first screen appears.