A menstrual cycle counts from the first day of one period to the first day of the next. Many adults have cycles somewhere between 21 and 38 days, and the length often changes a little from one cycle to the next.
The main phases
- Menstrual: bleeding, usually 3 to 7 days.
- Follicular: the time before ovulation, when the body prepares an egg.
- Fertile window: the days around ovulation when pregnancy is possible.
- Luteal: the time after ovulation. It is usually fairly steady in length, which is why the day of ovulation can be estimated backwards from the next period.
Why predictions are estimates
AuraCycle works out likely windows from your own recorded cycle lengths. The more period starts you log, the more useful the estimate becomes. A single unusual cycle does not mean something is wrong, but a clear, sustained change is worth discussing with a clinician.