Irregular periods

The average gap between periods starting (the menstrual cycle) is around 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 polyendocrine metabolic ovarian syndrome (PMOS) (which used to be called polycystic ovary syndrome PCOS) or thyroid problems, can cause irregular periods.

• your periods are irregular
• your periods last longer than 7 days
• you have irregular periods and other symptoms like weight gain, tiredness, hair growth on your face, and dry or oily skin
• you have bleeding between periods
• your periods are irregular and you're struggling to get pregnant

Treatment is not always needed for irregular periods.

The GP may refer you to a specialist 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 polyendocrine metabolic ovarian syndrome (PMOS) is causing irregular periods, the combined pill may help make your periods more regular.

If irregular periods are caused by other hormone problems, such as thyroid problems, medicines can help treat it.

Your periods are irregular if you have them more often than every 21 days or less often than every 35 days.

Causes of irregular periods include puberty, the start of menopause, pregnancy and some types of hormonal contraception.

Treatment is not always needed for irregular periods. If treatment is needed, it will depend on the cause.