Ovulation tests are at-home tools designed to predict when you’re about to ovulate. They work by detecting a surge in luteinizing hormone (LH) in your urine. This surge usually happens 24 to 36 hours before ovulation, which is your most fertile window. Why Ovulation Matters for Pregnancy Ovulation is the moment your ovary releases an egg. That egg lives for about 12–24 hours. Sperm, on the other hand, can survive up to five days. Timing intercourse around ovulation increases your chances of conception. That’s why many people visit website resources or guides to better understand this key moment.