Knowing what to expect can help your child feel prepared and help you know when it is time to check in with a doctor.

For many families, a first period brings up lots of questions. When will it start? How long should it last? How much bleeding is too much? Periods are a normal, healthy part of growing up. They can also tell us a lot about a child’s overall health, which is why doctors think of the menstrual cycle as a “vital sign,” just like heart rate or blood pressure.

When to expect a first period

Most kids get their first period, called “menarche,” around age 12 or 13. A helpful clue is breast development. The first period usually comes about two to three years after breast budding begins.

Because the first period can arrive without warning, we recommend packing a small “period kit” in your child’s backpack with a pad and a spare pair of underwear.

How long a period lasts and how often it comes

A period usually lasts seven days or less. A menstrual cycle is counted from the first day of one period to the first day of the next. For teens, a normal cycle is anywhere from 21 to 45 days, so periods may come as often as every three weeks or as far apart as about six weeks.

Irregular periods are normal at first

In the first one to two years after the first period, the brain and ovaries are still learning to work together. An egg is not always released each month, so periods may come early, come late or skip a month. The time between the first and second period is often the most unpredictable. By about the third year after the first period, most cycles settle into a more regular pattern.

We encourage kids to track their periods on a calendar or app, which makes it easier to notice patterns and share them with a doctor.

How heavy is too heavy for a period?

Most kids use three to six pads or tampons a day during their period. Bleeding may be heavier than normal if your child is:

• Soaking through a pad or tampon every one to two hours
• Bleeding for more than seven days
• Passing clots larger than about 1 inch (about the size of a quarter)

Heavy periods can lead to low iron, which may make a child feel tired, dizzy or short of breath. Sometimes heavy periods are a sign of a bleeding disorder, such as von Willebrand disease, especially when there is a family history of bleeding problems.

When to see a doctor about your child’s period

Talk with your child’s pediatrician or a pediatric and adolescent gynecologist if your child:

• Has not had a first period by age 15, or within three years of breast development starting
• Has periods that are regularly more often than every 21 days or less often than every 45 days
• Goes 90 days (about three months) without a period, even once
• Has periods that last more than seven days
• Soaks through a pad or tampon every one to two hours
• Has heavy periods along with easy bruising, frequent nosebleeds or a family history of a bleeding disorder
• Has pain that keeps them from school or activities or does not get better with ibuprofen or naproxen

Mild cramps are common with periods, but severe pain is not normal and should be checked by a doctor. If your child is bleeding heavily and feels lightheaded, faints or looks very pale, seek care right away.

Understanding what a normal period looks like helps kids and teens feel confident about their bodies and helps families know when a little extra support is needed.