Typical ranges. A cycle usually lasts 21 to 40 days and a period 2 to 7 days. Cycles can shift by a few days month to month.

How the estimates work. The dashboard averages the gaps between the start dates you log (up to the last 6). With fewer than 2 logged periods it assumes a 28-day cycle and a 5-day period. The more you log, the better it gets.

What moves it. Stress, illness, travel, big training changes, poor sleep and hormonal contraception can all change timing.

Not contraception. The fertile window here is a rough calendar guess. Don't rely on it to prevent or plan a pregnancy.

Worth a doctor's check if your cycles are often shorter than 21 or longer than 40 days, periods last more than 7 days or are very heavy, there's bleeding between periods, or pain stops you doing normal things.

This is her health information. Logging dates she has told you, with her knowing you track them, keeps it accurate and keeps it hers.