How do ovulation tests work?

Ovulation tests are simple at-home urine tests that help predict when a person will ovulate. You can use them if you’re trying to get pregnant or trying to avoid pregnancy. Read on to learn more about how ovulation tests work and what some of the pros and cons are of using them.

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Ovulation tests are at-home test kits that help you predict when you will ovulate (the time in your menstrual cycle when you can get pregnant). They’re also called ovulation predictor kits. They usually consist of test strips that you pee on or can dip in a cup of urine.People often use ovulation tests to time sex around “fertile days” to increase their chances of getting pregnant. Tests are also sometimes used by people trying not to get pregnant as part of a non-hormonal birth control option called the Fertility Awareness Method (FAM).

Ovulation tests measure the amount of luteinizing hormone (LH) in your urine. During your normal menstrual cycle, your hormones fluctuate up and down. LH is a hormone that spikes a couple of days before ovulation—that’s the phase of your cycle where your ovaries release an egg that a sperm can fertilize, and you can get pregnant (Holesh, 2021).

A positive result means that you have high luteinizing hormone levels, and you will likely ovulate within a couple of days. If it’s negative, it means that your levels of LH are low, meaning that you aren’t ovulating within the next couple of days.Sperm can live for nearly a week in the vagina, so a positive ovulation test means you are in your “fertile window”; if you have sex from now until two days after you ovulate, you have a higher chance of getting pregnant (Su, 2017).

Ovulation test strips are simple to use. 

You should read the product packaging for exact details, but most tests have you remove the kit from the packaging and pee on the test strip (or you can pee in a cup and dip the strip that way). 

The results typically appear in a window on the test kit within 10 minutes; usually, one line is the control line and means “negative,” and two lines (sometimes a smiley face) mean “positive.”

There are two things to consider with the timing of your ovulation test: what time of the month to test and what time of day to test.

Time of month to test 

To get the most useful results from an ovulation test, you’ll want to test a few days before you know you might ovulate. 

For people with regular 28-day cycles (those that are consistently the same number of days every month, roughly 28 days), ovulation is usually around day 14, about halfway through the cycle. Start testing on day 10 or 11 of your cycle (day 1 being the first day of your period) (Su, 2017). 

And if it takes you a few months of trial-and-error to figure out when you ovulate, that’s okay. Plenty of people aren’t tuned in to the specifics of their menstrual cycles, so it may take some time before you “catch” your pre-ovulation LH surges.

You can also tune in to your cycle by looking for physical signs of ovulation. These include changes in your body temperature (basal body temperature) and cervical mucus, as well as mid-cycle cramping or spotting. 

People with ‘irregular’ menstrual cycles (those that are unusually short, unusually long, or that vary from month to month) may need to take a few more tests per month to determine when they ovulate—more on this below.

Time of day to test

You can take your ovulation test at any time of day, but you should be consistent and take it at the same time each day. Some people recommend doing it first thing in the morning because LH levels tend to surge between midnight and 4 a.m. (Su, 2017). But there are no defined testing guidelines regarding the time of day to test. 

If you’re using ovulation tests to try and get pregnant, testing early in the day has the added perk of leaving plenty of time to have sex that day if it’s one of your fertile days.

Many people have cycles longer or shorter than 28 days or have irregular cycles and experience changes in menstrual cycle length. There’s a wide range of normal cycle lengths (between 21–35 days), and ovulation test kits can work for women with all cycle lengths (Bull, 2019). However, cycles on the shorter or longer end of the spectrum may require more trial and error to predict ovulation. 

If you have a shorter cycle (26 or fewer days), a longer cycle (more than 30 days), or an inconsistent number of days in your cycles, you’ll just need to test a bit more often. Take one test a few days after your period, and then every few days after that. You might be able to identify a consistent pattern every month, or it may change every month, and that’s okay. 

And as mentioned above, there are also physical signs—like changes in your cervical mucus—that you can look for that may clue you in to when you’re about to ovulate.

Like any medical tool, there are some pros and cons to using an ovulation test:

Pros

• It’s easy to find: Ovulation tests are available at any drugstore and are sold over the counter. They’re usually in the same place you find pregnancy tests.

• It’s easy and confidential to use: You can use the urine test stick privately, quickly, and in the comfort of your own home.

• It’s accurate: A systematic review (not done by ovulation test manufacturers) determined that at-home ovulation tests are 97% accurate; companies like Clearblue report their tests as being over 99% accurate (Su, 2017).

Cons

• It’s a prediction of ovulation, not a guarantee: Ovulation test strips are good at predicting ovulation, but that doesn’t necessarily mean you’ll ovulate for sure. Everyone’s body and cycle is different. The test predicts LH surge, not the release of the egg itself. Ovulation dates can still vary, plus your body may still not release an egg after the LH surge. That means the test’s information can’t be used with certainty to get you pregnant or keep you from getting pregnant. 

• It can get expensive: Ovulation tests aren’t cheap, especially if you’re testing multiple times a month for several months. They’re often sold in packs of 10, but, on average, the unit costs around $2–$3 per test—which can add up.

• It may be less reliable for some people: Ovulation tests may not be as reliable if you’re struggling with infertility, are using fertility-enhancing drugs, have conditions that cause hormone imbalances or irregular ovulation like PCOS (polycystic ovary syndrome), or are over the age of 40 (Rasquin Leon, 2021).

Ovulation tests can be a great tool for helping you to get pregnant, but they aren’t the be-all-end-all. If you’re trying to get pregnant and having difficulty, just know that there are a lot of other factors at play other than when you ovulate. iI other words, don’t get discouraged if you don’t get pregnant right away. 

There are many ways to increase your chances of getting pregnant (including maintaining your health and reducing stress) and timing sex with ovulation is just one of them.

If you’re trying to avoid pregnancy, ovulation tests can be useful tools to help you predict when you’ll ovulate—but they’re not reliable natural birth control on their own. You should use other indicators of fertility to help make sure you’re avoiding unprotected sex in the right window.

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

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Current version

May 13, 2022

Written by

Nancy LaChance, BSN, RN

Fact checked by

Chimene Richa, MD

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About the medical reviewer

Chimene Richa, MD

Dr. Richa is a board-certified Ophthalmologist and medical writer for Ro.