How to identify your most fertile days?

Dr Sarah Johnson

Reviewed by Dr Sarah Johnson on May 17, 2017
Written by Julie Macken.

There are only a few days (typically six) each cycle when you can get pregnant, the days leading up to and the day of ovulation. So, knowing when these days are in your cycle is key if you are trying for a baby. There are various signs and symptoms of ovulation and most methods of detecting ovulation rely on these to help you identify your fertile days. In this article, we look at these signs and symptoms and show how they can be used to help you:

How long it takes to get pregnant
  • Some methods can only identify when ovulation has already occurred, therefore they are of little value in helping a woman to conceive during that cycle.
  • Ovulation tests detect the LH surge which happens 24-36 hours before ovulation.
  • Clearblue Ovulation Tests are at least 99% accurate in detecting the LH surge.
  • The calendar method has been found to predict the correct fertile days in only a third of cycles1.


To maximize your chances of becoming pregnant, it’s important to time intercourse for the days leading up to and the day of ovulation. These are ways in which you can use the signs and symptoms of ovulation to help you identify these fertile few days each cycle.


Ovulation tests

Clearblue Ovulation Tests and the Clearblue Fertility Monitor are easy to use and detect the key fertility hormones from a urine sample. They are at least 99% accurate in pinpointing the LH surge and can identify up to six fertile days during each cycle when you are most likely to become pregnant.

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The calendar method

If you have a regular menstrual cycle, you can try to predict ovulation by carefully recording the length of each cycle. You will need to record the length of your cycle for at least a couple of months to start to build up a picture. For a very regular menstrual cycle, ovulation normally happens between 12 and 16 days before your next period starts. However, the day you actually ovulate can still vary by several days between cycles, even with a regular menstrual cycle.

In recent studies the calendar method has been found to predict the correct fertile days in only a third of cycles2

Basal Body Temperature (BBT) recording

This method uses the fact that your basal body temperature rises by 0.4-1.0°C after ovulation by which time it is too late to optimize the chances of conception in that menstrual cycle. To use this method accurately, you have to take your basal body temperature first thing every morning before moving out of bed, and it will take several menstrual cycles before you start to build up a picture of your fertility window. There are also many factors, like sleep cycles changes, travel, and alcohol consumption that can change your BBT. Studies have shown that using a woman’s basal body temperature to predict her fertile days (to within a day) is less than 70%2 successful.

Ovulation pain

Approximately one in five women have pain associated with ovulation. However, because the pain may occur during, or even after, ovulation this is often not that helpful to identify the days prior to ovulation and the day of ovulation itself when you are most fertile.

Saliva observations

It has been found that your saliva changes according to the amount of the hormone estrogen in your body, and there are kits available that can help you to monitor these changes. They usually consist of a tiny microscope with a glass surface – you place some spit on the glass surface, wait for it to dry and then look through the microscope for a ‘ferning’ pattern that is caused by salt crystals in the saliva when your estrogen level is high. However, changes in saliva have been shown to be an unreliable method of ovulation prediction and are hard to interpret2. Saliva can also be affected by smoking, drinking alcohol and eating.

Cervical mucus observations

During your menstrual cycle, the type and amount of cervical mucus (a secretion made by glands in your cervix) changes. It can be sticky or stretchy, white or cloudy. In the days leading to ovulation it becomes clear and stretchy and is often likened to egg white. By making a note of these changes, you can predict when you will ovulate so you can have sex on your most fertile days. The main advantage of this method is that it gives you a better understanding of your body, making you more aware of the changes your body goes through during a menstrual cycle. However, it can take time to learn how to ‘read’ the changes, and your cervical mucus can be influenced by other factors, including infections, sex and some medication


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In every cycle there are only a few days when a woman can conceive, so having sex on these days is very important if you are trying to get pregnant. The Clearblue® Advanced Digital Ovulation Test is the first and ONLY test that typically identifies 4 or more fertile days each cycle.

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