Ovulation prediction kits measure the concentration of the Luteinizing Hormone (LH) in your urine. This hormone is always present in small amounts in your urine but increases in the 24-48 hours before ovulation occurs. More advanced kits also measure estradiol, a form of estrogen that peaks on the day of ovulation. It’s a good idea to observe your cervical mucus to figure out when you are getting close to ovulation, since most kits provide only around 5 days’ worth of tests. Instructions vary from kit to kit, so read the product insert carefully. This testing method, unlike basal body temperature recording, can be used to guide the timing of intercourse.