This site has limited support for your browser. We recommend switching to Edge, Chrome, Safari, or Firefox.
How to use Ovulation Predictor Kits (OPKs)

How to use Ovulation Predictor Kits (OPKs)

If you’re trying to conceive, knowing when you ovulate is key and can help you to identify your fertile window. Ovulation Predictor Kits (OPKs) are a relatively easy way to track your fertile window. Here is what you need to know when using OPKs.

What is an OPK?

Ovulation test strips or ovulation predictor kits (OPKs) are urine based, at-home tests, you can use to determine when you’re ovulating. They work by measuring levels of luteinizing hormone (LH) in your urine.

An ovulation test kit usually comes with several tests which are to be used on a number of days. They can either be narrow test strips i.e. thin paper strips, or look more like plastic pregnancy test sticks. You either dip the test into a cup of your urine, or pee directly on to the tip of the stick. The results can tell you if you are likely to be in your fertile period and might be ovulating soon.

How do OPKs work?

OPKs detect luteinizing hormone (LH) which is the hormone released by the pituitary gland, to trigger ovulation. While the luteinizing hormone is always present in your urine, it increases 24-48 hours prior to ovulation. This LH surge triggers ovulation, in other words, the release of an egg from one of your ovaries. Ovulation test strips work by measuring the LH levels in your urine. Identifying the surge in LH can indicate that your body is entering the peak of the cycle and that ovulation may occur within the next 12 to 48 hours.

How to use an OPK?

For most women it makes sense to start to start testing around day 10 of their cycle. However, for women with irregular cycles it can be difficult to know when to start using ovulation tests. Some ovulation kits only come with around a week’s supply of tests, which may not be enough to cover the period during which ovulation might occur. In this case it can be beneficial to combine OPKs with another fertility awareness method such as checking cervical mucus. Waiting until you see signs of cervical mucus increasing before beginning to test with OPKs, might work better for some.

Try to take the OPK test at the same time every day until your positive LH surge. It can be good to test between 10am-2pm as LH hormone is typically released in the morning and may take a little time to end up in urine to be detected by OPKs. This can vary from person to person but if you are using OPKs first thing in the morning or late at night, and feel like you are missing your LH surge, try to change the time of day. Missing your LH surge can make you think you didn’t ovulate, when in fact, you may have ovulated but simply tested at the wrong time.

Try to reduce your fluid intake for about two hours before using the ovulation tracker kit. Excessive fluids will dilute your urine, which will make detecting your LH surge more difficult.

The OPKs should give you higher LH readings each day and subsequently a peak LH reading, where the test line is as dark as the control line. This will be the highest reading you will get and should indicate that ovulation will occur shortly – usually within the next 24 hours.

How to interpret the results

If the test line is as dark or darker than the control line, it is a positive result and should mean you will ovulate in 24-48 hours. This is a great time to get busy with your partner if you are trying to conceive

There are several reasons why you may go through all your test strips yet never see an LH surge. You may have started testing too early e.g. from day 13 to day 18, however you may not ovulate until day 20. Another possibility is that you started testing too late e.g you may have ovulated on day 12 but didn’t start testing until day 14. The longer your cycles are, the more likely it is that you ovulate later than average. The shorter your cycles are, the more likely it is that you ovulate earlier than average.

Another possible reason you won’t get a positive result is you’re not ovulating at all. If you don’t get a positive result after a few months, or if your cycles are irregular, talk to your doctor.


Why might OPKs not always work?

Ovulation test strips can do great job of letting you know when you’re most fertile. However they tend to be more accurate for some women than others. Ovulation predictor kits work best when your cycles are more or less predictable but can be less reliable in certain situations:

  • Ovulation tests may not work well for women with polycystic ovarian syndrome, who can have several LH surges or high levels of LH throughout their cycles.
  • OPKs may not work well if you have very irregular periods. Irregular cycles can make it tough to figure out when you’re due to start ovulating. That can increase the chances for using an ovulation predictor kit too early or too late and missing the ovulation window altogether.
  • If you are taking certain medications e.g. fertility drugs, hormones (like birth control pills) or antibiotics, it may make ovulation test strips inaccurate.

It’s important to remember that ovulation kits test for LH and not ovulation itself, and may sometimes yield false positive results. They can signal that your body is trying to ovulate, but they can't confirm that ovulation actually happened. It's possible for LH to surge and an egg to never release. There are a few possible explanations for an elevated LH level that doesn’t lead to ovulation. Here are some of them:

  • Polycystic ovary syndrome (PCOS)
  • Pituitary disorders
  • Perimenopause/menopause
  • Luteinized unruptured follicle syndrome (LUFS)

In another scenario, an LH surge preceding ovulation may have occurred but might have been missed altogether. For example, the LH surge may have only lasted for 10 hours and only testing once a day may actually miss the LH surge. As a result, some health care providers suggest doing the test twice a day and at least 10 hours apart, to pick up the LH surge.


In summary, ovulation test kits are a great tool for people who want to determine their fertile pattern and have been shown to have around 98% accuracy.

However, if you’ve tried ovulation test kits but haven’t been able to identify an LH surge or your ovulation window, contact your doctor with any questions.

Leave a comment

Please note, comments must be approved before they are published

Use coupon code WELCOME10 for 10% off your first order.


Congratulations! Your order qualifies for free shipping You are CHF 200 away from free shipping.
No more products available for purchase