Ovulation and fertility

If you have a normal monthly cycle there are a few days each month when you are more likely to get pregnant than others. This is because your ovaries have released an egg (known as ovulation), which can be fertilised by sperm.

What is ovulation?

Ovulation is when an egg is released from one of the ovaries during your menstrual cycle. The egg travels down the fallopian tubes to your womb. You can then get pregnant if the egg is fertilised by sperm. 

Occasionally, more than 1 egg is released during ovulation. If more than 1 egg is fertilised you can become pregnant with more than one baby.

If you don’t become pregnant, the egg is reabsorbed into the body. The lining of your womb, which has been getting thicker ready for a possible pregnancy, comes away and leaves your body as a period. It takes about 10 to 16 days for a period to start after an egg is released.

Ovulation doesn’t happen every month for every woman or birthing person. There are some health conditions that may interfere with ovulation, such as endometriosis and polycystic ovarian syndrome (POCS). If you are not getting a regular period and are trying to get pregnant, speak to your doctor.

When am I most likely to get pregnant?

You are at your most fertile just before you ovulate, on the day of ovulation, and up to a day after you ovulate. This week or so around when the egg is released is often referred to as the ‘fertile window’.

Sperm can live for around 7 days inside your body, so if you’ve had sex in the 5 days before ovulation, the sperm will still be ready when the egg to be released. 

If you can time sex to fall when you’re ovulating, that boosts your chances of conceiving even more.

Your ‘fertile window’

When you’re struggling to get pregnant finding out about your fertile window may turn into an all-consuming task. 

If you have regular, unprotected sex (sex every 2 to 3 days without contraception) you are likely to get pregnant. More than 8 out of 10 couples where the woman or birthing person is under 40 years old will get pregnant within 1 year if they have regular unprotected sex. 

Having said that, having sex every second day can be tricky for various reasons, particularly if pregnancy doesn’t happen quickly. That’s why being aware of your cycle and knowing about your fertile window can be helpful.

The tips below should help you figure out when you are at your most fertile. Be wary of relying too much on unscientific apps and tools which may narrow sex down to the wrong time each month.

Top tips for finding the fertile window

These are things you can do to track your cycle and find out when you are most fertile. 

Keep a diary of your menstrual cycle

The menstrual cycle is the time from the first day of a period to the day before the next period. 

Menstrual cycles vary in length. The average is 28 days, although both longer and shorter cycles are normal. It doesn’t matter how long your cycle is, ovulation usually happens 10 to 16 days before the start of your next menstrual cycle.

Keeping a record of when your periods start and stop will help you find your fertility window.

If you have a regular menstrual cycle you may be able to work out when you’re likely to ovulate, but be wary of narrowing it down too much, in case you get it wrong.

The following is based on a 28-day cycle. You'll have to adjust this depending on how much shorter or longer your cycle usually is.

  • Days 1 to 7: You have your period, which can last from 3 to 7 days.
  • Days 7 to 10: The lining of your womb gets thicker, ready for a possible pregnancy.
  • Days 10 to 16: Your fertile window.
  • Days 13 to 15: Your ovaries release an egg (ovulation). No matter how long your cycle, you will probably ovulate around 10 to 16 days before your next period starts.
  • Days 16 to 25: The womb lining carries on thickening.
  • Days 26 to 28: If you’re not pregnant the womb lining starts to come away again, leading to your next period.

Use an ovulation predictor kit 

A hormone called the luteinizing hormone (LH) increases in the urine (wee) before ovulation. Ovulation predictor kits (OPKs) test for rises in this hormone and may help pinpoint ovulation and the fertile window. However, there isn’t much evidence that using these kits actually improves conception rates.

If you decide to try using an OPK, you can buy them from pharmacies, supermarkets or online. They are simple to use. 

OPKs may not help you if you have a known fertility issue that affects your menstrual cycle, such as PCOS. This is because this condition affects your hormones, so you may not get an accurate reading. 

Talk to your GP if you have PCOS and want to get pregnant. You can also read more about trying to conceive with a long-term health issue.

It is best to get to know your usual menstrual cycle to help figure out when you should start testing. If you have an irregular cycle then an OPK can still help you pinpoint the time of ovulation, but you may end up using more of the test sticks. Follow the instructions on the packet to find out more.

Look out for ovulation symptoms

Some people may have breast pain, bloating and mild tummy pain when they ovulate. It’s not a guaranteed way of predicting ovulation, but If you notice a  pattern, it may help you get to know your cycle. 

Some people get a pain in one side of their lower abdomen (stomach area) when they ovulate. The pain can be a dull cramp or a sharp and sudden twinge.

Ovulation pain is often normal, but see your GP if you’re worried or if the pain is severe. Sometimes the pain can be caused by medical conditions that may affect your fertility, such as endometriosis or a sexually transmitted infection.

Check your cervix

The feel of your cervix changes when you’re close to ovulation. You can check your cervix by putting your clean finger inside your vagina. If it feels high and soft and not low and firm, you may be ovulating.

Look out for cervical mucus changes

Vaginal secretions (vaginal discharge) change during your menstrual cycle. If you’re ovulating, your discharge will be thinner and stretchy, a bit like raw egg white. There are apps that help you record and track cervical mucus changes.

Check your basal body temperature

You can use a thermometer to take your temperature every morning before you get out of bed (basal body temperature). This should be done before eating or drinking, ideally at the same time every morning. 

There’s a small rise in temperature (around 0.2C) after you’ve ovulated and until your next period. You will be least likely to be fertile at this point, so you need to chart your temperature for a few months, to see if there's a pattern to your cycle. If there is, you may be able to work out roughly when you'll next ovulate. There are apps that help you record and track your temperature.

The instructions around this method are very specific, so it is hard to get right and the results are less likely to be accurate.

Keep an eye on your sex drive

Research has found a link between hormone levels and sexual desire during a menstrual cycle. Plainly speaking, when you ovulate the hormones produced by the ovaries change, making your sex drive go up.

So, if you’re really in the mood, your fertility might be at its highest. How convenient!

Find out more about your fertile window.

Are you ready to conceive? Take our quick quiz to find out.

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Review dates
Reviewed: 22 March 2024
Next review: 22 March 2027