Predict your next 3 period dates and fertile windows based on your cycle.
Enter the most recent period start date, usual cycle length and period length, then generate the next three expected cycles and fertile windows.
Cycle length can vary, particularly with stress, illness, hormonal changes and life stage.
The period calculator predicts your next several menstrual cycles based on the date of your last period and your average cycle length. It helps with planning around menstruation, understanding your typical cycle pattern, and identifying when to expect your period in the coming months.
The menstrual cycle is counted from the first day of one period to the day before the next. A cycle shorter than 21 days or longer than 35 days, or significant variation from cycle to cycle, can sometimes indicate hormonal imbalances or conditions such as polycystic ovary syndrome (PCOS) or thyroid issues, and is worth discussing with a GP. Tracking your cycle over several months gives you the most accurate picture of your personal pattern — period tracking apps on your phone can complement this calculator for long-term logging.
No. This tool is for general planning and awareness only. Cycle-based contraception (fertility awareness methods) requires careful daily tracking of multiple indicators — including basal body temperature and cervical mucus — over many months, and should be taught by a trained practitioner. Relying on predicted dates alone for contraception is not recommended and carries a high risk of unintended pregnancy.