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1 Record the number of days in each cycle, including the day you start your period. 2  The last day of each cycle is the day before your next period starts. 3  Keep tracking your cycle this way for eight to twelve cycles. 4  The more cycles you have to reference, the more accurate the calendar method will be.
Use the calendar method. The easiest way to estimate when you'll ovulate is to count back. First, figure out what day your next period will probably start. (If your period is very irregular, this method won't work for you.). From that day, count back 12 days and then another four.