LH (luteinising hormone) rises shortly before ovulation. Ovulation tests detect this rise in urine. A rise usually means ovulation may follow within the next day or two, but a test cannot confirm that ovulation happened.
When people usually test
Test instructions usually suggest starting a few days before the middle of the cycle and testing at about the same time each day. Some people test twice a day because the rise can be short.
Reading the result
A test is usually read as positive when the test line is as dark as the control line, or darker. A faint line is usually read as negative, which is different from pregnancy tests. Brands differ, so always follow the instructions for your test.
In this app you read your own test and log what you see. The app never reads or judges a result.
Good to know
LH tests can be harder to use with irregular cycles or PCOS, where LH can be raised at other times. NICE guidance does not recommend timing sex around ovulation, because it can add stress, and suggests sex every two to three days instead. Your doctor can help you choose what fits you.