Using Ovulation Test Strips to Detect Your Most Fertile Time

Ovulation Predictor Kits, How They Work, and How to Use Them

Woman looking at an ovulation test strip
Ovulation test strips work a lot like pregnancy tests. You pee on them (or dip them in your urine) and then look at the lines to determine if you're ovulation or not. PhotoAlto/Ale Ventura / Getty Images

Ovulation test strips are urine-based tests that you use at home to detect impending ovulation. They work by detecting the hormone LH. Sometimes they are called OPKs, ovulation predictor kits, or simply ovulation tests.

When you buy an ovulation test kit, it comes with several tests strips (narrow thin papers), or they may look more like pregnancy test sticks. You either pee on the extended tip of the pregnancy-test-like version, or you pee in a cup and then carefully dip the test strip into your urine.


The results can tell you if you might be ovulating soon. (More on reading the results below.)

Using ovulation strips can help you time sex for pregnancy.

When you get a positive result on the test, you should have sex every day for the next two or three days.

Which Kind of Ovulation Strip Should You Buy?

There are a variety of ovulation predictor kits available. Clearblue Easy and First Response are the most popular.

Like pregnancy tests, you can pay relatively little or quite a lot, depending on how much technology you want.

The most expensive variety of ovulation predictors is digital.

The Clearblue Easy Fertility Monitor is one of the more popular digital tests. This monitor detects two hormones, LH and estrogen. This allows it to detect more fertile days than the paper tests. 

The cheapest ovulation tests are simply strips of paper. You can purchase the test strips online in bulk, but they often come with no instructions for use!

What you choose to buy and use has more to do with your comfort and your ease in reading the test strips. (They aren't always easy to interpret.)

A digital monitor takes the guess work out of ovulation testing, but it is pricey. Some people love the extra cheap test papers.

How Do Ovulation Predictor Kits Work?

Ovulation predictor kits work by detecting the levels of LH hormone in your urine.

As ovulation approaches, LH spikes.

This spike of LH is called the LH surge. About 36 hours after the LH surge, ovulation occurs.

To increase your chances of getting pregnant, you should have sex the two days before ovulation occurs.

Since OPKs detect the LH surge that occurs 12 to 36 hours before ovulation, you can be sure to have sex at just the right time for conception.

The Clearblue Easy Fertility Monitor detects LH and estrogen.

Because estrogen begins to rise before the LH surge, the Clearblue Easy Fertility Monitor can give you more warning that ovulation is coming. This will allow you to have conception sex for up to a week before you ovulate.

How Do You Use an Ovulation Predictor Kit?

Be sure to read the instructions of your particular ovulation predictor kit, since there may be slight variations on how they work.

Generally, however, an ovulation predictor kit comes with a set of test strips or sticks. Some OPKs come with five tests, others with as many as ten.

You should begin using the tests about two days before you expect to ovulate. If you’re not sure when you ovulate, you can use an ovulation calculator or the chart on this page:

If your cycles are irregular, you should test according to the earliest and latest dates you’d expect to ovulate.

Ovulation predictor kits have two lines.

One line is the control line. This just lets you know that the test was used properly and is working.

The second line is the test line. When the test line is as dark or darker than the control line, LH is surging.

This is when you should start having baby-making sex.

If you test for five days, you have an 80% chance of predicting ovulation. If you test for ten days, you have a 95% chance of predicting ovulation.

Clearblue Easy Fertility Monitor works differently from regular ovulation predictor kits. You need to start testing on the first day of your period.

Be sure to read the instructions carefully for the best results.

What Are the Advantages of Using Ovulation Predictor Kits?

Ovulation predictor kits are relatively easy to use.

Unlike charting your body basal temperature, you don’t have to remember to have a thermometer right by your bed or go crazy trying not to move too much when you wake up (to avoid messing up the results.)

Another advance of ovulation tests over BBT charting is that they tell you when ovulation is coming, not that ovulation has already passed.

Unless you are also checking your cervical mucus, a BBT chart can’t tell you when you should have sex. It can only tell you after it’s too late.

Also, ovulation kits don’t need to be used right when you get up. While morning urine is best, as long as you take the test within the same six-hour window every day, you should be able to get accurate results.

Another plus, if you're not comfortable checking for cervical mucus, you may feel better using the test strips.

What Are the Disadvantages of Using Ovulation Predictor Kits?

Using an ovulation predictor kit month after month can get expensive. This is especially so if your cycles are irregular and you need to use more than five test strips.

Some people have trouble reading a positive ovulation test result.

If you don’t get a very strong LH surge, you can drive yourself crazy wondering whether or not the test line is as dark as the control line or not.

If this is your situation, a digital test may be better. (But that will also be more expensive.)

Ovulation tests may not work well for those with PCOS.

Women with PCOS can have several LH surges or high levels LH throughout their cycles. This is the same reason they have increase cervical mucus throughout their cycles.

Since the ovulation kits test for LH, they may get positive results all the time or on several days. These positive results are false-positives -- they don't mean you're ovulating. 

Which brings up another possible problem with ovulation detection kits -- they can signal that your body is trying to ovulation. But they cannot confirm that ovulation happened.

It is possible for LH to surge and an egg to never release.

While ovulation predictor kits cannot confirm that ovulation actually took place, body basal temperature charting can.

Ovulation predictor kits can be used alongside other methods of ovulation detecting, like BBT charting. This can give you more assurance and help you get to know your body better.

You may want to use an ovulation predictor kit when you just start fertility charting for added confidence. Once you get the hang of charting your BBT and cervical mucus, you can drop the expensive ovulation test strips.

For women who find fertility charting stressful, though, ovulation predictor kits can be a great way to predict ovulation and time sex for pregnancy.


Ovulation Kits and Fertility Monitors. American Pregnancy Association. Accessed on February 14, 2011.

Patient Fact Sheet: Ovulation Detection. American Society of Reproductive Medicine. Accessed on February 14, 2011.



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