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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.
Simple with the period calendar: Calculate your period calendar based on your menstrual tracker history, or run Quick Calculate, to forecast your future periods. Also check if your period is late! Step 1. Select Calculation Rule. Your upcoming periods will be calculated based on your last period and average cycle length, as determined by your tracking history. To use this option, you need to be logged in. Your upcoming periods are calculated using the data specified below.