The app works effectively from the beginning and it takes around 1-3 cycles for the algorithm to get to know you.
When you start with Natural Cycles Prevent it’s normal to get many red days, and for users who Plan a pregnancy it's normal to get many brown days in the beginning - it means that Natural Cycles is getting to know your unique cycle and probably hasn’t detected your ovulation yet. For Prevent users, the app will only give you green days if it has enough data to do so.
It is highly individual how fast ovulation can be detected but it usually takes 1-3 cycles of measuring and adding data.
For users who have recently come off hormonal contraception, the first ovulation may only occur after a couple of months - this is normal and nothing to worry about. If you find yourself in that situation, be patient, and keep measuring. The red days will decrease with each ovulatory cycle as the app gathers more data on you.
The number of cycles it takes our algorithm to get to know you also depends on different factors such as: