Luteinizing Hormone (LH) tests help the NC° algorithm predict your ovulation by detecting the hormonal surge that happens right before an egg is released. Adding these results to the app helps the algorithm pinpoint your fertile window more precisely, which can give you more Green Days faster.
A positive LH test means your body is likely preparing to ovulate. However, it does not confirm that ovulation has happened — or that it definitely will happen.
Natural Cycles uses your temperature data to confirm whether ovulation actually occurred.
How to read strip-style LH test results
As a first step, please remember to always check the manufacturer's instructions on how to read the results of your ovulation tests. Below, you will find general instructions that most strip-style tests tend to follow.
Unlike a pregnancy test, where any faint line means positive, an LH test strip requires you to compare the darkness of two lines: the Test Line (T) and the Control Line (C).
- ❌ Negative Result (LH-): The Test Line (T) is lighter than the Control Line (C), or it does not appear at all. This means your LH surge has not started yet.
- ✅ Positive Result (LH+): The Test Line (T) is just as dark as, or darker than the Control Line (C). This means your LH surge is happening!
In the image below, you’ll find examples of positive (LH+) and negative (LH-) results on strip-style ovulation tests.
How to read digital ovulation test results
Digital tests can be tricky because some models show two types of fertile results: a blinking icon for "High" fertility (rising estrogen) and a solid icon for "Peak" fertility (the actual LH surge).
- Only log a Positive ovulation test in the NC° app when you reach your peak result.
- Do not log a positive result for "High" fertility days, as the algorithm specifically needs to track the peak LH surge to calculate your ovulation.
Because digital displays vary widely by brand and model, always double-check the booklet included in your specific test packaging to confirm which icon represents your Peak day.
Common Testing Scenarios & Errors
I got a positive and a negative test on the same day. What should I do?
Always log the Positive result in the app. The algorithm needs to know that a surge was detected at some point during that 24-hour window to map your cycle correctly.
What if all my tests are negative?
A negative ovulation test doesn’t mean that you're not fertile, and it also doesn’t mean that ovulation won’t happen – this is important to remember. A negative test only means that no LH surge was detected at the time of the test.
Because the LH peak happens in such a short window, it’s common to get negative ovulation test results, and some people may struggle with getting a positive result. This is highly individual, and depending on your body and medical history, the LH peak may be harder to catch for you than for others. To prevent the LH levels in the urine from diluting, you can try limiting the intake of fluids for a couple of hours before testing.
Ovulation can still occur, even if you've only gotten negative ovulation tests. Remember to continue logging your temperature every day, and the algorithm will still confirm your ovulation if your temperatures indicate ovulation has happened.
The Control Line didn’t appear at all. What does that mean?
If the Control Line (C) is missing entirely, the test is invalid (usually due to a manufacturing defect or using too much/too little urine). Do not log this result in the app. Discard it and try again with a brand-new test strip.
Read on to understand how ovulation test results influence ovulation detection, why you should take ovulation tests, and how and when to take ovulation tests.