Some women find that 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 to extreme weight loss and excessive exercise (see Irregular periods - causes for more information).
Irregular periods are common during puberty or just before the menopause. Treatment during these times is usually not necessary.
But if you're worried because your periods are particularly heavy, last a long time or are more frequent than monthly, or if you get bleeding or spotting between periods or after sex, see your GP. Read the box on this page for more specific advice on when you should see your GP.
You may need to switch to a different contraceptive or be investigated for an underlying health condition. See Irregular periods - treatment for information on the possible treatment options.
The average menstrual cycle
The average menstrual cycle lasts 28 days, but can vary between 24 and 35 days.
After puberty, most women develop a regular menstrual cycle, with around the same length of time between periods.
Menstrual bleeding normally lasts between two and seven days, with the average being five days.
More information on periods and period problems
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