The length of a menstrual cycle is calculated from the first day of your period to the first day of your next period. For example, if the first day of your cycle is on the 1st of July and the next period is on the 31st of July, then you have a 30-day cycle. Menstrual cycle length varies from woman to woman. It is usually 28 days on average, but it is also normal if the cycle length falls between 21 to 35 days. A menstrual period usually lasts for 3 - 7 days.
An irregular period means when your menstrual cycle length is constantly changing in a significant manner (more than 7 days difference). However, it is also abnormal if the cycle becomes too frequent (less than every 21 days) or too infrequent (more than every 40 days). You might also need to seek medical advice if your bleeding lasts for more than 7 days.
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