Some women find their menstrual cycle isn't always regular. Their periods may be early or late, and may vary in how long they last or how heavy they are each time.

Your normal menstrual cycle can be disturbed if you change your method of contraception, or if you have an imbalance of the reproductive hormones oestrogen and progesterone.

Many factors can cause a hormone imbalance, from polycystic ovary syndrome (PCOS) to extreme weight loss and excessive exercise.

Read more about the causes of irregular periods.

Treating irregular periods

Treatment for irregular periods may not always be necessary. However, you should see your GP if:

• you have bleeding or spotting between periods or after sex
• you have very heavy periods, where you need to change your tampon or pad every hour or two, or you have to wear both a pad and a tampon
• you experience heavy bleeding that floods into your bed or through your clothes 
• your periods last longer than seven days
• your periods are more frequent than once a month

You may need a different contraceptive, or further investigations may be needed to find out whether you have an underlying health condition.

Read more about treating irregular periods.

The average menstrual cycle

On average, a woman's menstrual cycle lasts 28 days, but cycles can vary from 24 to 35 days.

After puberty, most women develop a regular menstrual cycle, with around the same length of time between periods.

Menstrual bleeding usually lasts two to seven days, with the average being five days.

Periods and period problems

Read more about:

• periods (including an explanation of the menstrual cycle)
• heavy periods
• absent periods
• painful periods