How accurate are period-tracking apps and ovulation kits?

Trust the body signs and the kit over the app's prediction. Apps estimate ovulation from your past cycle lengths, so they're only reliable if your cycles are very regular. Ovulation (LH) test kits detect the hormone surge that happens roughly 24–36 hours before ovulation, so they're more accurate — though some conditions like PCOS can cause several surges without ovulation. Fertile cervical mucus (clear, stretchy, egg-white-like) is another useful sign. If your kit and app disagree repeatedly, or surges never lead to a period when expected, mention it to your doctor — an ultrasound follicle-tracking cycle can confirm if and when you ovulate.