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 ovarian syndrome to extreme weight loss and excessive exercise.

Read more information about the causes of irregular periods.

Treating irregular periods

Irregular periods are common during puberty or just before the menopause. Treatment during these times is not usually 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.

You may need a different contraceptive or be investigated for an underlying health condition.

Read more information about treating irregular periods.

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

Click on the links below for information on:

Menstrual cycle: animation

This animation explains in detail how the menstrual cycle works.

Media last reviewed: 21/02/2015

Next review due: 21/02/2017

When should I see my GP?

Talk to your GP if you have any of the following changes in your periods:

  • 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
  • your periods last longer than seven days
  • there are fewer than three weeks between the start of one period and the next
  • you have bleeding or spotting between periods
  • you are bleeding after sex

Page last reviewed: 04/04/2013

Next review due: 04/04/2015