Ovulation tests – how do they work and what is their purpose?

By (gynecologist), (gynecologist), (embryologist), (embryologist) and (biochemist).
Last Update: 11/18/2022

The ovulation test is a test used in women who are in the midst of trying to get pregnant, as it can help determine the fertile days of the menstrual cycle.

It measures the levels of the LH hormone in the urine, which increases when ovulation is about to occur.

These tests can be purchased at a pharmacy and are very easy to use: they work like a pregnancy test.

What is ovulation?

Ovulation is a process that takes place during a woman's menstrual cycle: a mature egg is released into the Fallopian tube where it waits to be fertilized by a sperm.

As such, ovulation is considered the most fertile stage of the menstrual cycle. This is when the probability of conception from sexual intercourse is at its highest.

Remember that a woman's menstrual cycle usually lasts about 28 days if it is regular, during which the following phases or stages occur:

is the degradation of the endometrium in the form of vaginal bleeding when fertilization has not ocurred.
Follicular phase
a new ovarian follicle with an egg inside begins to mature to the correct size.
Ovulatory phase
the mature follicle ruptures and expels the mature egg from the ovary into the fallopian tube.
Luteal phase
the egg is kept waiting to be fertilized and the endometrial thickness increases.

If you woud like more details about each of these phases, we recommend continuing your reading here: the different phases of the menstrual cycle.

Calculation of fertile days

In a regular 28-day menstrual cycle, ovulation usually occurs about halfway through, that is, about 14 days after menstruation.

Therefore, it seems easy to calculate the fertile days if the woman keeps track of her periods. If you trying for a baby, these days are recommended for unprotected sex.

Ovulation tests are very useful tools for women with irregular cycles and regular cycles other than 28 days long.

However, women with an irregular menstrual cycle will have a greater difficulty in calculating the fertile days, since ovulation may take place earlier or later.

In any event, ovulation tests are a reliable method to know which are the fertile day. Therefore the use of ovulation tests is advisable if you are considering having children.

How does an ovulation test work?

The ovulation test, also called the LH test, determines a woman's most fertile days by measuring the LH hormone in her urine.

LH is a pituitary hormone (secreted by the pituitary gland in the brain) that begins to increase in concentration about 36 hours before ovulation, a time known as the LH peak.

The ovulation test should be done daily to detect the highest level of LH. Once detected, sex is advised on the same day as the LH peak and the following one.

The average lifespan of an egg is about 24 hours. For this reason, it is important not to let this moment pass, so that the sperm can meet it for fertilization.

If this encounter does not take place, the couple will have to wait until the next cycle to try for pregnancy again.


When doing an ovulation test, it is important that the woman takes into account the following:

  • Check the menstrual cycle if possible and start using the tests towards the end of the follicular phase. This will avoid unnecessary testing expenses.
  • Take the test every day at the same time.
  • Do not urinate in the 4 hours prior to the test.
  • The easiest way is to test the first urine in the morning, as it will be less diluted, but it can be done at any other time.

In addition to all this, it is important to note that it is not recommended that the male have many abstinent days before ovulation takes place. Sperm quality is greatly reduced after several days without ejaculating.

It is best that there is not more than 3 days of abstinence while trying for pregnancy. It is also counterproductive to ejaculate several times a day, as the concentration of sperm will be diminished.

Types of ovulation test

There are different types of ovulation tests on the market, in terms of the medium used. Below, we will discuss each of them:

Ovulation test strips
is the simplest and most economical format, as per the Unitest brand. Bands appear on the strip after contact with urine. For a positive test, the band corresponding to LH must be of similar or equal intensity to the control stripe. If the LH band does not appear or is very light, it means that the woman is in her non-fertile days.
Digital Ovulation Test
the best known digital test is Clearblue. It has a more sophisticated format with easier to interpret results When the LH surge is detected a smiley face appears simply on the test screen.

As already mentioned, when the ovulation test is positive, it is advisable to have sex on the same day and for the next two days, so that the encounter between egg and sperm is more likely to take place.

FAQs from users

Can ovulation tests also used as pregnancy tests?

By Elisa Pérez Larrea M.D., M.Sc. (gynecologist).

As these two tests work by detecting different types of hormones, ovulation tests cannot be used as a pregnancy test.

An ovulation test is a test that helps to identify the time of ovulation, the most fertile period in a woman's cycle. The test detects elevated levels of luteinizing hormone (LH) in the urine.

In contrast, a pregnancy test detects the hormone Beta-HCG (Human Chorionic Gonadotrophin), whose level increases in blood and urine progressively as pregnancy progresses.

What does a negative ovulation test mean?

By Lydia Pilar Suárez M.D., M.Sc. (gynecologist).

When a woman takes an ovulation test and the result is negative, she may think that something is not right and/or that she has problems ovulating. However, a negative ovulation test can also be due to the following reasons:

  • The woman has done the test with the first urine of the morning, or without following the instrucitons correctly.
  • The patient has tested too far in advance of the LH peak (e.g. patient with long cycles).
  • The LH peak can be short (2 hours) and when the patient tested, it was too late for the test to be positive. It is therefore advisable to do it twice a day.
  • The sensitivity of the test used is low and does not detect the specific LH peak of the patient.

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How much do ovulation tests cost?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

The cost of ovulation tests depends on the brand, type and where you live.

In Spain, the Unitest test strip format is the most economical. A box with 25 strips costs about 11€ and a box with 50 strips costs about 20€. in contrast the Clearblue ovulation test with 10 tests is priced between 20-30€, so it is a bit more expensive.

In the UK a box of 20 tests of the Clearblue type costs between £25 - £50 depending on the brand and sensitivity of the test. Test strips are priced at around £10 for 50 test strips.

In the USA the digital tests cost around $40 for a pack of 20 and, the more economical test strips you can find for approximately $15 - $20 per box of 50.

For how many days is the ovulation test positive?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

The ovulation test will be positive whenever it is possible to detect the LH hormone in the urine. Normally, the fertile period lasts 5 days.

In ovulation tests with test strips, it will be possible to see the corresponding LH band intensifying, while digital ovulation tests will show a smiley face during fertile days.

When it is advisable to start using ovulation tests?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

This will depend on the length of each woman's menstrual cycle. The longer the cycle, the later the daily ovulation tests will be started in order not to waste tests.

For reference, in a 28-day menstrual cycle, the best thing to do is to start the ovulation test about 11 days after menstruation. Calculating accordingly, if the woman has a cycle of 24 days, she can start with the tests at 7 days of the menstruation or, conversely, if the cycle is 32 days, she can start at 15 days of her period.

My ovulation tests are always positive, what does this mean?

By Zaira Salvador B.Sc., M.Sc. (embryologist).

If the ovulation test is positive throughout the entire menstrual cycle, this means that the concentration of the LH hormone is elevated due to some alteration such as polycystic ovary syndrome (PCOS).

In this case, the woman should visit the gynecologist to check if there are any fertility problems and if she is ovulating correctly.

The same will happen if the ovulation tests are always negative, as this corresponds to anovulation problems.

How do I know when I ovulate?

By Marta Barranquero Gómez B.Sc., M.Sc. (embryologist).

Ovulation is a stage of the menstrual cycle and it is important to differentiate between regular and irregular menstrual cycles.

For women who have regular 28-day menstrual cycles, ovulation will occur on day 14 of the cycle, i.e. 14 days after their period.

For women with irregular menstrual cycles, however, it is difficult to know when ovulation will occur based on the previous cycle alone, as it can be earlier or later.

For this reason, one way of detecting the time of ovulation is by means of tests sold in pharmacies that measure the amount of the hormone LH. This hormone increases considerably when ovulation is about to occur.

What errors occur with ovulation tests?

By Marta Barranquero Gómez B.Sc., M.Sc. (embryologist).

It is important to carry out ovulation tests correctly and without making mistakes in their execution in order for the result to be valuable.

Each ovulation test is different, so it is important to read the instructions of each manufacturer carefully. In addition, faint lines do not mean that ovulation will occur. It is important that the line is as sharp or sharper than the control line.

If you are interested in learning more about the process of ovulation, you can carry on reading in the following article: What is ovulation?

There are other methods for detecting the fertile days, although they are less reliable than the ovulation test. You can find out more about this here: Use of cervical mucus as a fertility indicator.

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E J FARRIS. A test for determining the time of ovulation and conception in women. Am J Obstet Gynecol. 1946 Jul;52(1):14-27. doi: 10.1016/0002-9378(46)90355-9 (View)

Salmassi A, Schmutzler AG, Püngel F, Schubert M, Alkatout I, Mettler L. Ovulation detection in saliva, is it possible. Gynecol Obstet Invest. 2013;76(3):171-6. (View)

S Tiplady 1, G Jones, M Campbell, S Johnson, W Ledger. Home ovulation tests and stress in women trying to conceive: a randomized controlled trial. Hum Reprod. 2013 Jan;28(1):138-51. doi: 10.1093/humrep/des372. Epub 2012 Oct 18.

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FAQs from users: 'Can ovulation tests also used as pregnancy tests?', 'What does a negative ovulation test mean?', 'How much do ovulation tests cost?', 'For how many days is the ovulation test positive?', 'When it is advisable to start using ovulation tests?', 'My ovulation tests are always positive, what does this mean?', 'How do I know when I ovulate?' and 'What errors occur with ovulation tests?'.

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Authors and contributors

 Elisa Pérez Larrea
Elisa Pérez Larrea
M.D., M.Sc.
Dr. Elisa Pérez Larrea is a graduate in Medicine and Surgery from the University of Zaragoza and a specialist in Obstetrics and Gynecology from the University of Oviedo. She also has a Master's degree in Human Reproduction from the Complutense University of Madrid. More information about Elisa Pérez Larrea
Licence number: 203311163
 Lydia Pilar Suárez
Lydia Pilar Suárez
M.D., M.Sc.
Bachelor degree in Medicine and Surgery at the Universidad de Oviedo in Asturias. Specialization in Obstetrics and Gynecology at the University Hospital of San Carlos de Madrid. Master in Assisted Reproduction at the University of Rey Juan Carlos in collaboration with the Valencian Fertility Clinic IVI. More information about Lydia Pilar Suárez
Licence number: 64136
 Marta Barranquero Gómez
Marta Barranquero Gómez
B.Sc., M.Sc.
Graduated in Biochemistry and Biomedical Sciences by the University of Valencia (UV) and specialized in Assisted Reproduction by the University of Alcalá de Henares (UAH) in collaboration with Ginefiv and in Clinical Genetics by the University of Alcalá de Henares (UAH). More information about Marta Barranquero Gómez
License: 3316-CV
 Zaira Salvador
Zaira Salvador
B.Sc., M.Sc.
Bachelor's Degree in Biotechnology from the Technical University of Valencia (UPV). Biotechnology Degree from the National University of Ireland en Galway (NUIG) and embryologist specializing in Assisted Reproduction, with a Master's Degree in Biotechnology of Human Reproduction from the University of Valencia (UV) and the Valencian Infertility Institute (IVI) More information about Zaira Salvador
License: 3185-CV
Adapted into english by:
 Michelle Lorraine Embleton
Michelle Lorraine Embleton
B.Sc. Ph.D.
PhD in Biochemistry, University of Bristol, UK, specialising in DNA : protein intereactions. BSc honours degree in Molecular Biology, Univerisity of Bristol. Translation and editing of scientific and medical literature.
More information about Michelle Lorraine Embleton

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