Irregular periods are periods that don’t follow a typical pattern. For example, they might come earlier or later than expected.

The average length of a menstrual cycle is 28 days, and it’s common for periods to last from 3 to 7 days.

An irregular menstrual cycle is defined as:

• 8 or fewer menstrual cycles per year
• menstrual cycles shorter than 21 days
• menstrual cycles longer than 35 days.

For teenagers, an irregular cycle might mean periods:

• are longer than 90 days apart (more than a year after periods have started)
• are shorter than 21 days apart or longer than 45 days apart (between one and 3 years after periods started)
• have not started by the age of 16.

Irregular periods can be frustrating because they are unpredictable, and you may not have period products when you need them. It can also make it hard to plan a pregnancy.

Irregular periods are common in the first 2 years after your first period. They often become more regular over time.

Your periods can become irregular as you approach menopause and after pregnancy.

Irregular periods may be due to:

• dieting or eating disorders
• smoking
• excessive exercise
• lack of exercise
• being overweight or underweight.

They may also be due to:

• polycystic ovary syndrome (PCOS)
• premature ovarian insufficiency (POI)
• pregnancy
• medicines (e.g. hormone medicines)
• stress.

See your doctor if you’re worried about your periods becoming irregular.

There are other reasons why you might need to see your doctor about your periods.

It’s helpful to record information about your periods and take it with you to discuss at your appointment. You can record:

• when you get your periods
• the length and heaviness of your periods
• how your periods affect you.