ForeFlight Mobile displays 'Effective' and 'Expires' dates for the airport data that is stored on your device. This information is accessible on the 'Airports' page under Airports > Info > Cycle. You can also view this information on the 'Downloads' page which is under More > Downloads.
If an item within ForeFlight Mobile is expired, a red banner will display across on the screen to make sure you know.
Additionally, ForeFlight Mobile will show you a notification when new data sets are available by displaying a red circle with a number on the ForeFlight Mobile app icon and on the 'More' button within ForeFlight Mobile. To update your data set, open ForeFlight Mobile and go to More > Downloads and download any available items. You can learn more about this in the downloads section of our Pilot's Guide.