An ovulation test is a simple urine test that detects a surge in luteinizing hormone (LH), the chemical signal your body sends to trigger the release of an egg from your ovary. When the test picks up that surge, it means you’re likely to ovulate within the next 24 to 36 hours, placing you in your most fertile window. These tests are about 90% accurate at detecting the LH surge when used correctly, according to the FDA.
How Ovulation Tests Work
Throughout most of your menstrual cycle, LH stays at a low, steady level. Then, roughly midway through your cycle, your body releases a sharp spike of LH that tells the ovary it’s time to release a mature egg. Ovulation tests are designed to catch that spike.
Most standard test strips are set to trigger a positive result when LH reaches about 25 mIU/mL, though some brands use a threshold as high as 40 mIU/mL. Because everyone’s baseline LH level is different, the threshold your body needs to cross can affect which brand works best for you. Once the test detects the surge, you’re in the narrow window when conception is most likely.
One important distinction: a positive ovulation test predicts that ovulation is about to happen, but it doesn’t confirm that an egg was actually released. Your body can produce an LH surge and still fail to ovulate in some cases. Progesterone-based urine tests (sometimes called PdG tests) exist specifically to confirm ovulation after the fact, by detecting a hormone your body only produces in meaningful amounts after an egg has been released. Together, the two types of tests give a fuller picture of what’s happening in your cycle.
Types of Ovulation Tests
The most basic and least expensive option is a standard test strip, which works like a pregnancy test. You dip the strip in urine and wait for lines to appear. One line is the control (confirming the test worked), and the second is the test line. If the test line is as dark as or darker than the control line, the result is positive. These strips are cheap enough to use daily, but reading line intensity takes some practice.
Digital ovulation tests remove the guesswork. Instead of interpreting line darkness, you get a clear “yes” or “no” indicator, often displayed as a smiley face. Some advanced digital monitors track multiple hormones, not just LH, and pair with smartphone apps to map your fertile days across several cycles. These cost more per test but are easier to use confidently.
When and How to Test
The best time to test is with your second morning urine, roughly between 10 a.m. and noon. First morning urine can actually miss the surge because LH takes about four hours after entering your bloodstream to show up in urine at detectable levels. If the surge starts overnight, your earliest sample may not contain enough of the hormone yet.
For the most reliable results, reduce your fluid intake for about four hours before testing. Drinking a lot of water dilutes your urine and can lower the LH concentration below the test’s detection threshold, leading to a false negative. Test at roughly the same time each day so you’re comparing consistent samples.
When to start testing depends on your cycle length. A common approach is to begin about 17 days before you expect your next period. If your cycle is 28 days, that means starting around day 11. If your cycles are irregular, you may need to test for a longer stretch each month.
Reading Your Results
On a standard strip test, a faint test line does not count as positive. This is a key difference from pregnancy tests, where even a faint line usually means a positive result. With ovulation strips, the test line must be equal to or darker than the control line to indicate a true LH surge. A light line simply means LH is present at its normal baseline level.
Once you get a positive result, your most fertile window is the next 24 to 36 hours. Having intercourse on the day of the positive test and the following day gives the best chance of conception, since sperm can survive in the reproductive tract for several days while the egg is viable for only about 12 to 24 hours after release.
A negative result means either LH hasn’t surged yet or you’ve already passed the surge. If you’re testing consistently and never see a positive, it could mean you’re missing the window, your baseline LH is unusually low, or ovulation isn’t occurring that cycle.
When Results Can Be Misleading
Polycystic ovary syndrome (PCOS) is the most common reason ovulation tests give unreliable results. Women with PCOS often have chronically elevated or erratic LH levels. One study found that women with PCOS had average LH levels of about 12 mIU/mL even outside of ovulation, compared to roughly 2.4 mIU/mL in women without the condition. That elevated baseline can sit above the test’s positive threshold all month long, producing false positives that suggest ovulation is imminent when it isn’t.
The opposite problem also occurs with PCOS. LH levels can pulse up and down unpredictably, so you might catch a dip and assume you’re not approaching ovulation when you actually are. If you have PCOS and are trying to conceive, ovulation tests alone may not give you reliable information. Tracking additional signs like basal body temperature or working with a fertility specialist can fill in the gaps.
Other situations that can throw off results include perimenopause (when LH levels tend to run higher), certain fertility medications that contain LH or affect its production, and testing too early or too late in your cycle. Recently stopping hormonal birth control can also cause irregular surges for a few months while your cycle recalibrates.
What Ovulation Tests Can and Can’t Tell You
Ovulation tests are a useful, accessible tool for timing intercourse during your fertile window. They reliably detect the LH surge about 9 out of 10 times, which makes them a solid first step for anyone trying to conceive or simply trying to understand their cycle better.
What they can’t do is confirm that ovulation actually happened, diagnose fertility problems, or tell you anything about egg quality. They also can’t detect pregnancy (despite some internet claims that they can, since LH and pregnancy hormones are structurally similar). If you’ve been using ovulation tests with well-timed intercourse for several months without success, the next step is typically a more comprehensive fertility evaluation that looks at hormone levels through blood work, checks for structural issues, and evaluates both partners.