Ovulation Tests: How They Work & When to Test

What Are Ovulation Tests?

Ovulation tests, often called ovulation predictor kits (OPKs), are tools that help you identify your most fertile days by detecting a hormone called luteinising hormone (LH) in your urine. LH rises sharply right before ovulation, signaling that your body is preparing to release an egg.

This LH surge typically happens 24 to 36 hours before ovulation. So when your ovulation test turns positive, it's a strong sign that you’re entering your most fertile window. This is the ideal time for intercourse or home insemination if you’re trying to conceive (TTC).

Ovulation tests can be especially helpful for those with irregular cycles, PCOS, or anyone who doesn’t want to rely on general app predictions. They give real-time insight into your actual biology, not averages.

So in simple terms: a positive OPK means you’re about to ovulate, and it’s the best time to have intercourse or inseminate.

How Do Ovulation Tests Work?

Ovulation tests detect the LH hormone in your urine. This hormone is secreted by the brain’s pituitary gland and helps signal the ovary to release a mature egg. A sudden spike, known as the "LH surge," tells your body it’s time to ovulate.

The test strip contains special antibodies that react with LH if it's present. When the hormone reaches a certain level (often around 20–25 mIU/mL), it binds to the antibodies and causes a chemical change, usually a visible coloured line.

There are two lines: a control line (to show the test is working) and a test line (to indicate LH presence).

• If the test line is lighter than the control, it’s negative.

• If it’s just as dark or darker, it’s positive, and you’re likely to ovulate soon.

Digital versions use the same science but display results with smiley faces or words like “peak” and “high.”

Now let’s talk about the test itself. Many OPKs are narrow, hard to read, and result in faint, confusing lines. That’s why we created Ovadetect. It features a 5mm-wide ovulation test strip that’s easier to handle, less likely to streak or smudge, and far clearer to read. It’s designed for people who want accuracy without the stress of guesswork.

Wider strips allow for more even dye flow and a more defined result. This clarity matters, especially if you’re testing early in the morning, at work, or on the go. It also helps if you have short LH surges or hormonal variations that make traditional strips unreliable.

When Should You Start Testing?

This depends on your cycle length. You want to start testing a few days before your expected ovulation to ensure you catch the surge.

• If your cycle is 28 days, start testing on Day 10.

• If your cycle is shorter (e.g. 25 days), start around Day 7.

• If it’s longer (e.g. 32 days), begin around Day 12.

Count Day 1 as the first day of full-flow bleeding, not spotting.

If your cycles are irregular, start testing earlier and test consistently until you detect a surge. You may need to test twice a day (morning and evening) to catch the peak if it’s brief.

Tips for Best Accuracy

• Test at the same time each day, preferably in the late morning or early afternoon when LH tends to be more concentrated.

• Avoid testing with first-morning urine, as LH can take time to metabolise and appear in urine after it surges in blood.

• Reduce fluid intake about an hour beforehand to avoid diluting your sample.

• Consider testing twice a day if you have short surges. Try once around 11 a.m. and again in the early evening.

• Use a high-quality test strip that offers visual clarity and sensitivity. Ovadetect is a great example that makes spotting your LH surge far easier.

What Happens After a Positive Ovulation Test?

Once you detect your LH surge, ovulation will likely occur within 12 to 36 hours. This is your prime fertile window.

• If you’re using donor sperm or doing home insemination, aim to inseminate within 12–24 hours of the positive test.

• If you’re timing intercourse, aim for the day of the positive result and the following day.

After ovulation, LH levels drop and OPKs will return to negative. Testing past this point won’t provide useful information.

Are Ovulation Tests 100% Accurate?

While ovulation tests are one of the best tools for identifying your fertile window, they are not foolproof.

A positive test tells you that your body is gearing up to ovulate, but it doesn’t confirm that ovulation actually happens. In some cycles, especially for people with PCOS or hormonal imbalances, you might get an LH surge but not release an egg. This is called a luteinised unruptured follicle (LUF), where the follicle matures but fails to rupture.

Also, some people have short or subtle LH surges that are easy to miss. Others might have multiple surges before actual ovulation. If you rely on just one test per day, you might miss it entirely. That’s why testing twice daily or combining with other signs (like cervical mucus or basal body temperature) gives you a fuller picture.

Still, OPKs are far more accurate than simply using calendar predictions. When used properly and consistently, they help time intercourse or insemination during the most fertile window. For many, that’s a huge step forward.

Ovulation tests are a powerful tool in your TTC toolkit. Like any tool, they work best when you understand their limits and how to use them alongside other signs from your body.

They don’t confirm ovulation, but they give you a strong signal when your body intends to ovulate. Pair that with cycle tracking, cervical mucus observation, and post-ovulation symptoms like BBT shifts, and you’ll feel more confident in your timing.

And if you’re looking for something clearer, easier to use, and better suited to irregular cycles, that’s where Ovadetect shines. Its wide 5mm strips, fast dye flow, and clear results provide peace of mind.