Period Calculator

How Menstrual Cycle Predictions Work

Your menstrual cycle is measured from the first day of one period to the first day of the next period. Regular cycles typically range from 21 to 35 days, with 28 days being the standard average.

Calculating Future Periods and Fertility

• Period Dates: The start of your next period is projected by adding your cycle length to the start date of the last period. The period ends based on your input bleeding duration. Formula: $\text{Next Start} = \text{Previous Start} + \text{Cycle Length}$ and $\text{Next End} = \text{Next Start} + \text{Period Duration} - 1\text{ day}$.
• Ovulation Date: Ovulation typically occurs 14 days before the start of the next menstrual period (assuming a standard luteal phase). Formula: $\text{Ovulation} = \text{Next Start} - 14\text{ days}$.
• Fertile Window: Since sperm can live up to 5 days, the fertile window spans 6 days in total: the day of ovulation and the 5 days leading up to it.