A menstrual cycle is counted from the first day of bleeding in one month to the first day of bleeding in the next month. The average menstrual cycle is about 28 days, but cycles that are 21–45 days also are normal. It may take 6 years or more after your period starts for your cycle to get regular. Why is it a good idea to track my period? If you do this every month, you may notice a pattern. It may become easier to tell when you will get your next period. Check online or on your smart phone for apps that can help you track your period. How can I track my period on a calendar? To track your period on a calendar, mark the first day your bleeding starts on a calendar with an X. Put an X on each of the following days that you have bleeding. Count the first X as day 1. Keep counting the days until you have your next period.