The average gap between periods starting (the menstrual cycle) is 28 days. It can sometimes be a bit shorter or longer.

A woman's periods are irregular if the gap between them is less than 21 days or more than 35 days.

Irregular periods can affect anyone who has periods.

It's more likely for your periods to be irregular when they first start during puberty, and when you're nearing menopause.

Keeping track of your periods

Using an app or a diary to keep track of your periods can help you see if they're irregular.

Day 1 of your menstrual cycle is the first day of your period. The last day of your cycle is the day before your next period.

Common causes of irregular periods include:

• puberty, when you start your periods
• the start of menopause (usually between the ages of 45 and 55)
• pregnancy – a missed period is often an early sign of pregnancy
• hormonal contraception like the progestogen-only pill , contraceptive injection and intrauterine system (IUS)
• losing or gaining a lot of weight
• stress and anxiety
• exercising too much

Sometimes, conditions like polycystic ovary syndrome (PCOS) and an underactive thyroid gland can cause irregular periods.

Treatment is not always needed for irregular periods.

The GP may refer you to a specialist (gynaecologist) if you need tests to find out what's causing your irregular periods. If treatment is needed it will depend on the cause.

For example, if a condition like polycystic ovary syndrome is causing irregular periods, the combined pill may help make your periods more regular.

Getting pregnant can be more difficult if you have irregular periods because you might not release an egg (ovulate) regularly.

It can help to have sex every 2 or 3 days throughout your cycle without using contraception.

If you're struggling to get pregnant, hormone medicine or fertility treatment may be recommended.

Read more about trying to get pregnant .