Monitoring the number of days in your menstrual cycle helps you figure out when you’re ovulating and if your bleeding pattern is normal.

A series of hormone events happens in your brain, ovary, and uterus — it ends with menses or bleeding. Even though it’s the final event, it’s also the most obvious. So this is what you use to count your cycle.

Cycle length is the number of days from the first day of one period to the start of the next period. It varies for each woman. The length of a normal cycle can vary from 21 to 45 days. But in any one woman, it typically varies only by 3-4 days from month to month.

Normal menses last from 2-7 days. There should be no spotting in between periods.

You should count day 1 of your cycle as the first day that you bleed — even if the flow is light. If you have a day of very minor spotting before flow, you can use either day to count as your day 1. But be consistent from month to month.

If the total number of days that you show any blood lasts more than 7 days, this is an abnormal pattern. If the lengths of your cycle or the days of flow are consistently abnormal, make an appointment with your doctor.