Our guide to ovulation tests

Whether you are new to trying to conceive (TTC) or have been trying for some time, ovulation tests are useful tools to help provide guidance when timing your baby making. With so many different ovulation tests available, we’ve produced this guide to support you and provide a little more detail about how they work and their differences.

The basics about ovulation and getting pregnant

Before choosing the right ovulation test for you, it helps to have an understanding about why timing ovulation can be so important when TTC.

Ovulation is when an egg is released from the ovary. An egg lives for about 12-24 hours after being released. To become pregnant, the egg must be fertilised by a sperm within this time. Sperm can live inside the female body for around 5 days, so sex doesn’t have to occur at the precise time the egg is released for the woman to become pregnant. Therefore, having unprotected sex during the 4-5 days before ovulation, through to the first 24 hours after ovulation, can result in pregnancy. These 6 days are what is known as your ‘fertile window’. However, a woman is most likely to become pregnant if she has unprotected sex within a day or so of ovulation.

How do ovulation tests work?

There are different types of ovulation tests that work in different ways.

Hormone tests

These are simple test strips that detect the levels of certain hormones in the woman’s urine. The level of luteinising hormone (LH) in a woman’s urine peaks approximately 24-36 hours before ovulation. Ovulation test strips can be used to detect this peak and therefore help to identify the 2 most fertile days per cycle

Some ovulation test strips detect oestrogen as well as LH. Oestrogen levels begin to rise before the LH surge is detected, helping to identify 4 or more fertile days per cycle.


Basal Body Temperature

    When a woman ovulates, the release of progesterone causes her body temperature to increase very slightly by about 0.5-1°C. By measuring basal body temperature (BBT) it is possible to identify when a woman has ovulated. By tracking this, along with other indicators or fertility algorithms, it is possible to predict when ovulation may occur and when the fertile window is. A fertility algorithm is a set of rules that are applied to fertility data based upon huge amounts of evidence and are used to calculate the most likely outcome.

    BBT is a measurement of the lowest body temperature at rest, usually taken orally or with a specific fertility thermometer.

    Do ovulation tests work for everyone?

    Standard hormone ovulation tests that detect LH can only predict ovulation where an LH surge is present. It is important to remember that not all women ovulate in each cycle. Standard LH ovulation tests are trying to detect a surge above what is considered a normal level, but not everyone has ‘normal’ LH levels. Some women with polycystic ovary syndrome (PCOS) can have high levels of LH even when they are not ovulating which can lead to a false positive result.

    Other ovulation tests, including some fertility monitors, can be limited in that they can only predict ovulation in women with regular cycles of specified lengths.

    Before choosing the right ovulation test or fertility monitor for you, make sure you carefully read the information available, so you are sure it suits your needs.

    What’s the difference between an ovulation test and a fertility monitor?

    It is understandable with so many devices available that people ask, what is the difference? Generally speaking, an ovulation test gives you an indication that you are either about to ovulate or that you just have ovulated. You can use this information to help to time your baby making.

    A fertility monitor will also do this, but often also has the ability for you to record your cycle dates and when you have had sex. Many fertility monitors use scientific data to build algorithms that, when combined with the ovulation test function, can give you more accurate and predictive fertile windows. A number of fertility monitors can also do pregnancy testing too.

    For women who have been unsuccessful trying to conceive using ovulation kits or fertility monitors, our new fertility services, offering private online video consultations with a doctor or nurse, may help you to better understand your fertility and the challenges you face when trying to conceive:

    Why Can’t I Get Pregnant?

    Getting Pregnant With Polycystic Ovary Syndrome (PCOS)



    You must be over 18 years old to use our service. Dr Fertility’s services are not to be used for any diagnosis or treatment that may require a physical examination or in a medical emergency. If you have a medical emergency, you must immediately call 999 or NHS 111.

    Dr Fertility does not offer assisted reproductive technologies such as IVF. Our services are paid for private healthcare services that are separate from any NHS treatments that you are currently having or may have in the future.

    Ovulation test and fertility monitor summary

    To help make things easier, we’ve provided a breakdown of all the ovulation tests and fertility monitors we offer with the key features of each one. To learn even more about each test, visit the product page for that particular product.





    Great feature 

    Ovulation tests 

    Clearblue Advanced Digital Ovulation Test Kit with Dual Hormone Indicator  

    10 x ovulation tests (LH and oestrogen) 
    20 x ovulation tests (LH and oestrogen) 

      Not suitable for women with PCOS 

      Over 99% accurate in detecting the LH surge 

      Identifies 4 or more fertile days 

      Clearblue Digital Ovulation Test Kit  

      10 x ovulation tests (LH) 

        Not suitable for women with PCOS 

        Over 99% accurate in detecting the LH surge 

        Identifies 2 or more fertile days 

        Clearblue Connected Ovulation Test System 

        25 x ovulation tests (LH and oestrogen) 


          Not suitable for women with PCOS 

          Over 99% accurate in detecting the LH surge 

          Connects via Bluetooth to your phone 

          Identifies 4 or more fertile days 

          Clearblue Trying for a Baby Kit – 10 ovulation tests and 1 pregnancy test 

          10 x ovulation tests (LH and oestrogen) 
          1 x pregnancy test (hCG) 

            Not suitable for women with PCOS 

            Over 99% accurate in detecting the LH surge 


            Pregnancy test is 99% accurate from the day your period is due 

            Comes with a Clearblue Rapid Detection pregnancy test included 

            Identifies 4 or more fertile days 

            FertilTime Ovulation Test (5 tests) 

            5 x ovulation tests (LH) 


              Not suitable for women with PCOS 

              Over 99% accurate in detecting the LH surge 

              Great value for money to identify your 2 most fertile days 


              Fertility monitor 

              Clearblue Advanced Fertility Monitor 

              Contains NO test sticks 


                Clearblue Advanced Fertility Monitor Refill Test Sticks (24 tests) sold separately 

                20 x ovulation test sticks (LH) 
                4 x pregnancy test sticks 


                  Not suitable for women with PCOS or cycles outside 12-42 days 

                  Over 99% accurate in detecting the LH surge 


                  Ovulation testing, pregnancy testing and fertility tracking all in one device 

                  Identifies up to 6 fertile days 

                  OvuSense Fertility and Ovulation Monitor 

                  1 x OvuSense Fertility monitor that measures Vaginal core body temperature 12-month subscription to the OvuSense app 


                    Suitable for women with PCOS, low ovarian reserve and irregular periods. 

                    99% accurate at confirming ovulation and 96%  accurate at giving you a 24hours prediction of ovulation. 8-day fertile window’ 

                    Takes your temperature every 5 minutes while you sleep 

                    Identifies your entire fertile window at the start of each cycle 

                    myLotus Fertility Monitor 

                    20 x Ovulation Tests (LH) 
                    3 x Pregnancy Tests (hCG) 

                      myLotus Refill Pack sold separately 

                      20 x ovulation Tests (LH) 
                      3 x pregnancy Tests (hCG) 



                        Suitable for women with PCOS, unexplained infertility and irregular periods. 

                        Ovulation tests are over 99% accurate 


                        Pregnancy test is 99% accurate from the day your period is due 

                        Numerically identifies your baseline luteinising hormone (LH) levels making it suitable for women with PCOS 


                        Always buy your ovulation tests from a reputable supplier. All ovulation tests sold by Dr Fertility carry a CE mark to show they comply with EU health, safety and environmental requirements. Always store your ovulation tests in a cool, dry environment, as shown on the packaging. Always use before the expiry date. Read the manufacturer’s instructions carefully and use exactly as described.


                        1.     NHS [Online content accessed 30.07.20]
                        2.     Medical News Today [Online content accessed 30.07.20]
                        3.    A Comprehensive Textbook of Midwifery & Gynaecological Nursing, By Annamma Jacob. Chapter 70, Page 659
                        4.    Su HW, Yi YC, Wei TY, Chang TC, Cheng CM. Detection of ovulation, a review of currently available methods. Bioeng Transl Med. 2017;2(3):238-246. Published 2017 May 16. doi:10.1002/btm2.10058
                        5.    Clearblue - “The mean duration of the combined high and peak fertility days detected was 6.01 ± 2.33 days, in a laboratory analysis of daily urine samples from 352 menstrual cycle”


                        Last updated on: 18/08/2020   Review by: 18/08/2023