Most ovulation kits detect luteinizing hormone (LH). A positive result indicates an LH surge, which usually precedes ovulation by about 24–48 hours. Some digital tests also measure estrogen (E3G) alongside LH to identify additional fertile days.

Strip-style tests use color indicator lines or plus/minus marks. Some kits use digital displays that show icons or short messages (for example, 'High' and 'Peak' often shown with a smiley icon) to indicate fertility levels.

Strip tests have a control line and a test line. A test line that is equal to or darker than the control line indicates an LH surge (positive), while a lighter or absent test line indicates no LH surge.

Kits use urine as the sample; some tests are held directly in the urine stream for about five seconds, while strip tests are dipped into a urine sample for about 3–5 seconds.

Digital tests use screens with icons or messages to show fertility levels—for example, a blank circle for low fertility, a flashing smiley for high fertility, and a static smiley for peak fertility—and label days as 'High' or 'Peak'.