Apps can display a small red oval containing a white number on their app icon to indicate when new and important information is available.
Make badging intuitive. People should know why your app icon is badged and how to find the related information when they open your app.
Use badging for notification purposes only. Badges shouldn't be used to display other types of numeric information, such as air quality, dates, stock prices, or weather.
Minimize badging. Don’t overwhelm users by connecting badging with a huge amount of information that changes frequently. Instead, use badging for focused, essential information that requires attention and atypical content changes that are highly likely to be of interest.
Draw attention to important information inside your app too. If you rely solely on app icon badging to highlight information, you run the risk of people missing it. Make sure critical information is also clearly presented inside your app.
Avoid using alerts in conjunction with badging. Even when new or important information is available, users don't want to see an alert the moment they open your app. Instead, focus on making the information discoverable.
Keep badges up to date. Update your app’s badge as soon as the corresponding information is read. You don’t want people to think new or important information is available, only to find that they’ve already seen it.