The menstrual cycle - your questions answered

Samantha Wild
Clinical Lead for Women's Health and Bupa GP
11 March 2024
Next review due March 2027

When it comes to your menstrual cycle, you may have more questions than answers. No two cycles are the same, and it can be hard to know what’s typical and what’s not. Here, I explore some common questions about the menstrual cycle and periods.

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What is a period?

A period is the vaginal bleeding that happens at the start of your menstrual cycle. You may also see periods being described as “menstruation” or a “menstrual period”.

The menstrual cycle is the time from the first day of your period to the start of your next period. This is roughly 21 to 35 days.

Why do periods happen?

In each cycle, hormones are released and cause changes to prepare your body for pregnancy. Your womb lining thickens. One of your ovaries then releases an egg into your womb. If sperm does not fertilise the egg, the womb lining breaks down. It then leaves your body through your vagina. Period blood is made of blood and tissue from your womb lining.

When do periods start and stop?

Periods start during puberty, at around 12 to 14 years old. But they can start earlier or later than this age.

When your periods have stopped for over 12 months, this is called menopause. This usually happens at 45 to 55 years old. The transition to menopause is called perimenopause. After the start of perimenopause, it can take from a few months to eight years or more to reach menopause.

How do I know if my period is normal?

Everyone is different, so it can be hard to define what’s normal. But most people who have periods are likely to notice the following things.

  • Your period happens every 21 to 35 days and lasts between two and seven days.
  • You’ll lose roughly up to six tablespoons or up to 80ml blood each period. This means you’ll use around three to six pads or tampons each day of your period.
  • Your period blood may be different colours depending on how heavy your flow is. It could look bright red, dark red, brown or black.
  • You may pass small blood clots on your heavy days.

How do I know if my period is heavy?

Regularly losing more than 80ml blood is considered a heavy period. This is around five to six tablespoons or more. But it can be hard to track how much blood you’re losing. The following are signs of a heavy period.

  • You bleed through your clothes or bedding.
  • You need to change your pad or tampon very often, such as every hour.
  • You need to use two sanitary products at the same time.
  • You pass large blood clots (larger than a 10p coin).

Sometimes heavy periods can stop you from doing daily activities, like working, shopping or going out.

Why is my period irregular?

Periods usually happen every 21 to 35 days. But if you have irregular periods your period might happen more or less often than this. Or you might find that your periods are unpredictable. Below are some reasons why periods may be irregular.

  • First period. When you first get your period, your cycle may be longer or shorter than average as you aren’t ovulating regularly yet. After you’ve been having periods for three years, you’re likely to have an average cycle length.
  • Perimenopause. Your periods may become irregular or unpredictable before you reach menopause.
  • Certain conditions. These include polycystic ovary syndrome, endometriosis, fibroids, sexually transmitted infections, adenomyosis or thyroid problems.
  • Increased stress. Stress (both mental and physical) may affect your periods temporarily. If you try to reduce your stress levels, your periods should return to normal.
  • Breastfeeding. If you’re breastfeeding and not using any baby formula, your period may not start again until you stop breastfeeding. If you start to breastfeed less often, you might experience a light and irregular period.

Other potential causes include extreme weight gain or loss, extreme exercise, long-distance travel, jet lag and shift work.

Irregular periods may be typical for some people. But for others there might be an underlying condition.

How do I track my period?

You can track your period by keeping a period diary. This can be in the form of a physical diary, or you could use a period tracking app. You can track things such as your blood flow, mood, energy level, pain level and other symptoms.

Keeping a record can help you to see what’s normal for you. It can also help you to notice any changes or patterns in your cycle. This can be a useful tool for identifying potential health problems.

When should I seek medical advice for my menstrual cycle?

Each person’s periods and menstrual cycle is different. What may be typical for some may not be for others. But it’s best to see your doctor if:

  • you’re 16 years old and your period hasn’t started yet
  • your periods suddenly stop for more than 90 days and you’re not pregnant, breastfeeding or nearing menopause
  • your usual period cycle changes suddenly and you’re under 45 years old
  • your period is very heavy or very painful 
  • you have periods more often than every 21 days or less often than every 35 days
  • your periods or premenstrual syndrome (PMS) symptoms stop you from doing your usual daily activities
  • you feel very anxious or depressed around the time you have your period
  • you bleed between periods

Each of these may be a sign of a potential health problem. So it’s always important to seek medical advice about what you’re going through. Your doctor can help you to manage your menstrual cycle and identify any issues.

If you have heavy, painful, or irregular periods, you’ll know just how disruptive they can be, both physically and mentally. With our Period Plan, you don’t have to face these problems alone.

Samantha Wild
Dr Samantha Wild
Clinical Lead for Women's Health and Bupa GP



Atiya Henry, Health Content Editor at Bupa UK

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