Predict your next period and track your cycle — private, instant, free
This calculator predicts your next period based on a regular cycle length. The average cycle is 28 days, but normal cycles range from 21–35 days. Your fertile window is typically Days 10–17 of your cycle (around ovulation at Day 14 for a 28-day cycle).
This tool is for general tracking only. For medical advice, speak with your healthcare provider.
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The Period Calculator predicts your upcoming menstrual periods, your likely fertile window and ovulation day based on your last period date and your typical cycle length. It gives a simple monthly forecast so you can plan ahead.
The tool adds your cycle length to the first day of your last period to project the next start date: next period = last period start + cycle length. Ovulation is estimated at roughly cycle length − 14 days, and the fertile window spans about five days before ovulation to the day after, reflecting sperm and egg survival times.
Use it to anticipate your next period for travel or events, to identify your fertile window when trying to conceive, to spot when a cycle seems unusually early or late, or simply to keep a private, quick record of your cycle timing.
Enter the first day of your last period and your average cycle length; the calculator adds the cycle length to project your next start date.
A typical cycle is around 28 days, but anywhere from 21 to 35 days is considered normal, and it can vary from month to month.
Yes. All predictions are calculated in your browser and your dates are never sent to or stored on a server.
They are estimates based on a regular cycle. Irregular cycles, stress and health factors can shift dates, so treat forecasts as a guide rather than a guarantee.