Enter your usual cycle length in days. Many people have cycles between 21 and 35 days, but some cycles are shorter or longer.
The app automatically works out your next period date, a likely ovulation day and a few fertile days around it. Everything stays saved on this device only.
These calculations use averages: ovulation is often about 14 days before the next period. Every body is different. If your periods change a lot, or you have strong pain, always ask a health professional for advice.