Period Calculator

A menstrual cycle is the monthly series of changes a woman’s body goes through in preparation for the possibility of pregnancy. Each month, one of your ovaries releases an egg — a process called ovulation. At the same time, hormonal changes prepare the uterus for pregnancy. If ovulation takes place and the egg isn’t fertilized, the lining of the uterus sheds through the vagina. This is a menstrual period.

The average menstrual cycle is 28 days long, but normal cycles can range from 21 to 35 days. The length of your cycle is calculated from the first day of your period to the day before your next period starts. Cycle length can vary from person to person and can also change over time for the same person.

Your fertile window is the six days leading up to and including ovulation. Ovulation typically occurs about 14 days before your next period starts. For someone with a 28-day cycle, this would be around day 14. However, this can vary based on your individual cycle length. The most fertile days are the three days leading up to and including ovulation.

Common menstrual symptoms include cramping, bloating, breast tenderness, mood swings, headaches, and fatigue. These symptoms are caused by hormonal changes and typically begin a few days before your period starts and may continue into the first few days of your period. While some discomfort is normal, severe pain or very heavy bleeding should be discussed with a healthcare provider.

This period calculator provides estimates based on the information you provide. It’s most accurate for people with regular menstrual cycles. If you have irregular cycles, are approaching menopause, have recently given birth, or are using hormonal birth control, the predictions may be less accurate. This calculator is not a substitute for medical advice and should not be used for contraception purposes.