Ovulation tests: how do they work and how reliable are they?

You’ve decided to have a baby. You’ve read every article on conception, you know your cycle like the back of your hand, and now you're wondering if ovulation tests are really the miracle solution for getting pregnant. Spoiler alert: it's more complicated than that.

At Puissante, we believe in transparency. Ovulation tests can be useful, but they are not foolproof. Before you fill your pharmacy basket with dozens of test sticks, we’ll explain how they really work, what they detect, and, most importantly, their limitations.

How does an ovulation test work?

Let’s start with the basics. An ovulation test detects luteinizing hormone, or LH, in your urine. This hormone surges suddenly 24 to 36 hours before your ovary releases an egg. This is what is known as the “LH surge.”

When you take an ovulation test, you are measuring the level of this hormone in your urine. If the level exceeds the test's detection threshold, the result is positive. In theory, this is your signal that ovulation is approaching and that it’s the right time to have sex to maximize your chances of conception.

The thing is, ovulation tests only detect the LH surge. They do not confirm that ovulation actually occurred. That is an important distinction.

The reliability of ovulation tests: the truth

Here is what you are generally told: ovulation tests are 99% reliable for detecting the LH surge. This is indeed what manufacturers claim, based on laboratory tests. But be careful, this figure does not mean that you have a 99% chance of getting pregnant by using them.

According to the study Urinary-Based Ovulation and Pregnancy: Point-of-Care Testing, the reliability of urine tests is indeed very high for detecting a hormonal surge. However, detecting the LH surge is not synonymous with guaranteed conception. There are several reasons for this.

First, there is the question of the “fertile window.” Even if you detect the LH surge, the egg only lives for 12 to 24 hours. Sperm, on the other hand, can survive for 3 to 5 days in the female reproductive tract, as noted by the French National Health Insurance. So technically, you have a window of about 6 days to conceive: the 5 days leading up to ovulation and up to 24 hours after.

Then, there is the problem of unsuccessful ovulation. You read that right: even if your ovulation test is positive, sometimes the ovary does not release an egg. In some cases, the follicle does not rupture despite the LH surge. Stress, illness, or a fever can also delay ovulation, or even cause multiple LH surges during a single cycle. You get a positive result, you rush to have sex, and... nothing happens.

Finally, not all tests are equal. During a DGCCRF investigation conducted in 2022-2023, 2 out of the 6 ovulation tests analyzed were non-compliant, notably because their performance levels were not indicated. Choose a CE-marked test with instructions in your language.

When to take an ovulation test?

This is a question many people ask. The answer depends on the regularity of your cycle.

You have a regular cycle

If you have a regular 28-day cycle, ovulation usually occurs around day 14. In this case, you can start testing 3 to 4 days before this expected date, i.e., around day 10 or 11. Continue testing daily until you get a positive result.

For other cycle lengths, a simple rule of thumb is to start testing about 17 days before the expected date of your next period:

You have an irregular cycle

If your cycle is longer or shorter, or if it is irregular, it is more complicated. You must first observe the length of your cycles over several months. Then base your calculations on your shortest cycle to estimate your ovulation date and start your tests: you are less likely to miss the surge. Also expect to use more tests.

Ovulation test: the ideal time

The ideal time to test? The one indicated in your test's instructions, as guidelines vary by brand. Some digital tests should be used with the first urine of the morning. Conversely, many strip manufacturers advise against using the very first urine and suggest testing in the late morning or early afternoon instead. In many women, LH is secreted early in the morning and takes a few hours to appear in the urine.

In any case, avoid drinking a lot and, if possible, urinating in the 4 hours before the test: urine that is too diluted can skew the result.

Always test at the same time each day for consistency. Regularity is key, because the LH surge can be short-lived and you could miss it if you test irregularly.

If you want to better understand your body, check out our article on the symptoms of successful ovulation.

The different types of ovulation tests

There are two main types: strips and digital tests.

Strips are the most affordable. They generally cost between 10 and 20 euros for a pack of 20. You collect a little urine in a clean glass or cup, then dip the strip in for a few seconds. You wait a few minutes and you have your result.

The test is positive when the test line is as dark as, or darker than, the control line. If it is lighter, the LH surge has not yet been detected.

Digital tests (such as Clearblue) are more expensive (30 to 50 euros for 10 to 20 tests) but easier to read. They clearly display a smiley or a symbol when the LH surge is detected. No doubt about interpreting the result.

Regardless of the type you choose, follow the instructions to the letter. Do not exceed the test area marked on the strip, read the result within the indicated time frame (not after), and don't leave the test sitting around for too long before throwing it away.

Where to find ovulation tests?

You can buy them in pharmacies, drugstores, supermarkets, and of course online. Prices vary depending on where you buy them and the brand, but you will easily find affordable options.

The limitations of ovulation tests: what you need to know

Now, let’s talk about the things that make ovulation tests less reliable than people think.

PCOS makes things complicated

If you suffer from polycystic ovary syndrome (PCOS), ovulation tests become much less reliable. Why? Because PCOS is often accompanied by a hormonal imbalance with a high baseline level of LH. This means you could get a positive result even if you are not about to ovulate.

Some manufacturers even specify that their tests are not suitable for people with PCOS. If this applies to you, talk to your gynecologist: medical monitoring (ultrasounds, hormonal tests) provides a much more reliable idea of your ovulation.

Want to know more about PCOS? Check out our full article on the subject.

Ovulation is not guaranteed

As mentioned earlier, an LH surge does not necessarily mean successful ovulation. Even if your test is positive, your body may not release an egg. It’s frustrating, but it’s the reality.

False-positive or false-negative results

Yes, it can happen. A defective strip, incorrect usage technique, or inadequate urine concentration can yield inaccurate results.

Some situations can also skew the result:

• a current or recent pregnancy, including after a miscarriage: the pregnancy hormone (hCG) resembles LH and can make some tests react;
• perimenopause and menopause, during which LH levels remain high;
• certain fertility treatments, especially hCG injections;
• hormonal contraception, which generally blocks ovulation and makes the test useless.

Conversely, a very short LH surge can go unnoticed and make the test seem “always negative.”

Important reminder: an ovulation test is not a method of contraception. Since sperm can survive for several days, the LH surge arrives too late to avoid a pregnancy.

Alternatives to ovulation tests

If you find ovulation tests too expensive, too stressful, or simply unreliable for you, there are other methods to track your ovulation.

Symptothermal method

The symptothermal method combines several observations: your body temperature, your cervical mucus, and other physical signs, such as the position of your cervix.

After ovulation, your body temperature rises slightly (about 0.3 to 0.5 °C) due to progesterone. By taking your temperature every morning and noting your observations, you can confirm that ovulation has occurred. Unlike ovulation tests, the symptothermal method allows you to confirm ovulation after it has happened.

The symptothermal method is one of the most comprehensive natural ways to know where you are in your cycle… provided you are diligent and well-trained in the method.

Cervical mucus observation

Your cervical mucus changes throughout your cycle. Before ovulation, it becomes more abundant, clearer, and more elastic, resembling raw egg whites. This is a sign that you are approaching your fertile period. This method is free and requires no equipment.

Menstrual cycle tracking

If your cycle is regular, you can simply estimate your ovulation date by subtracting 14 days from the date of your next period. This is only an average, as the phase following ovulation lasts from 10 to 16 days depending on the woman. So, it is not as precise as tests, but it is a good starting point.

Tracking apps

Apps like Flo or Clue predict your fertile period based on your data. Their predictions are based on averages: they do not replace ovulation tests, but they can help you track your menstrual cycle and understand it better.

The real questions to ask yourself

Before investing in ovulation tests, ask yourself these questions:

Do I have a regular cycle? If so, ovulation tests will be more useful. If not, you might struggle to determine when to start testing.

Am I patient? Ovulation tests can take time. You may need to test for several days before getting a positive result. If the idea of taking a test every day stresses you out, it might not be for you.

Am I in good reproductive health? If you have PCOS, ovulation tests could be less reliable for you. In case of endometriosis or other gynecological issues, the test may work, but conception may take longer: don't wait to talk to a healthcare professional.

How long have I been trying to conceive? If it’s been less than 6 months, ovulation tests can be useful. Beyond that, the French National Health Insurance advises consulting after 12 months of trying without pregnancy if you are under 35, and after 6 months if you are over 35 or have a known medical issue.

Optimizing your chances of conception

Ovulation tests are just a tool. To really maximize your chances of conception, you can also:

• Maintain a healthy lifestyle: a good diet, regular exercise, and enough sleep support your fertility.
• Reduce stress: stress can affect your menstrual cycle and ovulation.
• Have regular sex: you don't need to wait for the day of ovulation. Having sex every 2 to 3 days throughout the cycle increases your chances.
• Consult a professional: if you have doubts about your fertility, consult a gynecologist or a fertility specialist.

To learn more about natural ways to boost your fertility, check out our dedicated article.

The key message

Ovulation tests can be useful for identifying your fertile period, but they are not foolproof. They detect the LH surge, not actual ovulation. Use them as one tool among others to track your cycle, not as the ultimate solution for getting pregnant.

If you have been trying to conceive for more than a year without success (or more than 6 months if you are 35 or older), or if you have concerns about your fertility, consult a healthcare professional. Your doctor, midwife, or gynecologist can help you identify any underlying issues and suggest solutions tailored to your situation.

You deserve to be supported on your conception journey. Whether you use ovulation tests or other methods, do what works best for you.