Cycles aren't regular, so just adding an event every 27th day in your calendar, won't be of much use to a lot of women. These apps can get quite good at predic

Cycles aren't regular, so just adding an event every 27th day in your calendar, won't be of much use to a lot of women. These apps can get quite good at predicting irregular cycles. Some apps will give users warnings of the type "PMS starts tomorrow, expect moodswings", or "expect extreme tiredness" and for people who are heavily affected by their period, this can be a big help in controlling their feelings or just understand their well-being.