The Natural Cycles app will give you a daily fertility status in the big circle with a supporting text inside on the Today view.
Red days: Use protection
Red days are days where you may be fertile. On all red days, you should use protection (we recommend condoms) or abstain from vaginal intercourse.
Red days will be displayed by a red circle and the words Use protection on the Today view.
The algorithm will give you red days to cover your fertile window (six days per cycle) plus some additional days to account for possible variation in your ovulation day from cycle to cycle. Once your window of red days has started in a cycle, you will continue to get red days until the algorithm confirms your ovulation and that your fertile window has passed.
Keep in mind that it will take a few cycles for the algorithm to get to know your unique cycle, so you may experience more red days in your first few cycles.
Green days: Not fertile
Green days are days where you are not fertile, which means that you do not need to use protection when having sex.*
Green days will be displayed with a green circle and the text Not fertile on the Today view.
The algorithm will only give you a green day if it is certain, based on the data you have logged, that you are not fertile for that day — either by confirming that you have already ovulated or that you are unlikely to do so in the coming five days (due to sperm survival).
You may get your first green days as early as in your first cycle. As the algorithm gets to know your unique cycle, you will experience more green days. Exactly how many green days you get may vary from cycle to cycle and it will depend on factors such as when you usually ovulate, how much your ovulation varies and how much your temperature varies from day to day.
You can trust the very first green day you are given, as long as you see it on the Today view. This means that you have to check your daily fertility status each day before having sex and not rely on previous predictions.
*Keep in mind that the only method of contraception that protects against STIs is the male and female condom. Should you have a reason for concern, be sure to use them regardless of fertility status.