Period Calculator
Estimate your period days and most probable ovulation days for the next six cycles, from the first day of your last period, how long it lasted, and your average cycle length.
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The menstrual cycle
The menstrual cycle is the series of changes the body runs through each month in preparation for a possible pregnancy. It usually begins between the ages of 12 and 15 and continues until menopause, which occurs on average at 52. A cycle is counted from the first day of one period to the first day of the next, is driven by the rise and fall of hormones, and lasts 28 days on average — though lengths vary, and a cycle is considered regular when the longest and shortest vary by less than 8 days.
Across the cycle, the lining of the uterus thickens and an egg matures. The egg is released at ovulation — the most fertile point of the cycle, roughly the five days before ovulation through one to two days after it. If the egg is not fertilized, pregnancy cannot happen: the lining sheds as a period, and the cycle restarts. A period — menstruation — is that regular discharge of blood and mucosal tissue through the vagina, usually lasting 2 to 7 days, in the opening (menstrual) phase of the cycle. Periods pause during pregnancy and typically don't resume during the early stages of breastfeeding, and they end permanently at menopause — usually between 49 and 52, and defined as twelve months with no vaginal bleeding.
This calculator projects the two things worth planning around: the period days themselves (when bleeding and discharge occur) and the most probable ovulation days in each cycle.