How to Calculate Menstrual Cycles
- 1). On a calendar, note the exact day that your last menstrual period began as Day 1. Mark an X on that day.
- 2). Count each day on the calendar until your next period begins, and mark an X on that day. That date is Day 1 of your latest menstrual cycle.
- 3). Go back and count the number of days between the start of your last menstrual cycle and the start of your latest period. That number is the length of your menstrual cycle.
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