Know your cycle.
Log your period, see your real average, and get an estimate of what is coming. Everything stays on your phone. Nobody else sees it, not us and not your employer.
How the estimates work
Your cycle is counted from the first day of one period to the first day of the next. Log a few and the app works out your own average instead of assuming the textbook 28 days, which plenty of women do not have.
On the fertile window: ovulation is estimated by counting back about 14 days from your next expected period, and the window covers the five days before it plus one after, because sperm can survive that long. It is an estimate built on an average, so it moves when your cycle moves.
This is not birth control. Around 12 to 24 in every 100 women relying on calendar methods get pregnant within a year. If you are trying to avoid pregnancy, a polyclinic or GP can talk you through options that actually work.
If your cycles are irregular, the app shows a range rather than a single date, because pretending to know the day would be worse than admitting it does not. Irregular cycles are common and usually harmless, but a doctor should hear about them.