Apple HealthKit is an integration with Apple’s Health app, which allows you to sync your data from different apps into one Health app. Our integration with Health kit enables you, for instance, to import fertility data into Natural Cycles from the Health app, in case you were tracking your fertility before and don’t want to start from scratch with Natural Cycles.
You can also back up your data collected with Natural Cycles into the Health app if you wish to. In the Apple Healthkit app, you can enable which data you would like to sync. This functionality is only supported on iOS devices and not on Android.