How Often Does a Girl Get Her Period?

Just as some girls begin puberty earlier or later than others, the same applies to periods. Some girls may start menstruating as early as age 10, but others may not get their first period until they are 15 years old.

The amount of time between a girl's periods is called her menstrual cycle (the cycle is counted from the start of one period to the start of the next). Some girls will find that their menstrual cycle lasts 28 days, whereas others might have a 24-day cycle, a 30-day cycle, or even longer. Following menarche, menstrual cycles last 21-45 days. After a couple of years, cycles shorten to an adult length of 21-34 days.

Irregular periods are common in girls who are just beginning to menstruate. It may take the body a while to sort out all the changes going on, so a girl may have a 28-day cycle for 2 months, then miss a month, for example. Usually, after a year or two, the menstrual cycle will become more regular. Some women continue to have irregular periods into adulthood, though.

As a girl gets older and her periods settle down — or she gets more used to her own unique cycle — she will probably find that she can predict when her period will come. In the meantime, it's a good idea to keep track of your menstrual cycle with a calendar.