Is there a good iOS app that uses temperature tracking for natural birth control?

Natural Cycles Fertility App is specifically designed for women seeking hormone-free birth control through temperature monitoring. The app requires daily basal body temperature measurements, which it analyzes using a proprietary algorithm to determine fertility status. Users receive clear daily indications of whether they're in a fertile (red day) or non-fertile (green day) phase. The app integrates with wearable devices like Oura Ring for automatic temperature syncing, eliminating manual entry. Clinical studies show the app has a typical use effectiveness rate of 93% for preventing pregnancy. Beyond contraception, the same temperature data can help users understand their menstrual cycles and identify ovulation patterns when trying to conceive. Some users note the subscription cost may be higher than typical period tracking apps, though this reflects its medical device classification and clinical validation. The learning curve for proper temperature measurement requires consistent morning routines, but most users adapt within a few cycles.