Period tracker

Your average cycle length is measured from the periods you log (the most recent six). Ovulation is predicted by counting back 14 days from your next expected period — the luteal phase after ovulation is the consistent part of a cycle, while the phase before it is where cycles vary. The fertile window is the five days before ovulation plus ovulation day itself, because sperm can survive up to five days and the egg about 24 hours. Both rules follow the American College of Obstetricians and Gynecologists’ guidance on fertility awareness and Johns Hopkins Medicine’s fertility-window guide.

Predictions are averages projected forward, so they sharpen as you log more periods — and they degrade when cycles are irregular. If your cycles vary by more than a week, fall outside 21–35 days, or you are postpartum, breastfeeding, or recently stopped hormonal contraception, calendar predictions can miss your real fertile window entirely; the tracker warns you when your own data shows this.

The water goal defaults to 2,000 ml of drinks a day, in line with the U.S. National Academies’ adequate-intake guidance (~2.7 L total daily water for women, roughly 80% of it typically from drinks) — and it is adjustable, because activity, climate and bodies differ. The care tips are general wellness suggestions tied to your cycle phase and logged symptoms, not personalised medical guidance.