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You must be over the age of 18. Does not protect against STIs.
Natural Cycles is 93% effective with typical use, 98% effective with perfect use.
When you start using Natural Cycles, it can take some time to get to know your unique cycle, resulting in an increased number of Red Days during your first 1-3 cycles. This ensures that the app is effective from the first day of use. Once Natural Cycles has detected your ovulation, you are likely to receive more Green Days. You can rely on the fertility status indicated by the app from the first day of use.
The number of fertile/non-fertile days you get will vary. As every body is different, there is no set number of Red Days you will receive. Although we're only actually fertile for six days in any menstrual cycle, the number of Red Days you get depends on the regularity of your cycle, how often you input data into the app, and the stability of your body temperature. The algorithm will also give an extra Red Day or two as a buffer for extra protection in case your ovulation day moves.
Give the algorithm time to learn your cycle and try to measure at least five days a week to increase the number of Green Days.