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 not give green days without having enough information 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, it's not unusual to not have an ovulation for a couple of months so don't be worried - be patient and keep measuring. The red days will decrease with each ovulatory cycle with 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: